What Is Antioxidants? – Types, Health Benefits

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 13 min read
Patient Tools

Read, save, and share this guide

Use these quick tools to make this medical article easier to read, print, save, or share with a family member.

Patient Mode

Understand this article easily

Switch between simple English and easy Bangla patient notes. This is for education and does not replace a doctor consultation.

Antioxidants are man-made or natural substances that may prevent or delay some types of cell damage. Diets high in vegetables and fruits, which are good sources of antioxidants, have been found to be healthy; however, research has not shown antioxidant supplements to be beneficial in...

For severe symptoms, danger signs, pregnancy, child illness, or sudden worsening, seek urgent medical care.

বাংলা রোগী নোট এখনো যোগ করা হয়নি। পোস্ট এডিটরে “RX Bangla Patient Mode” বক্স থেকে সহজ বাংলা সারাংশ যোগ করুন।

এই তথ্য শিক্ষা ও সচেতনতার জন্য। এটি ডাক্তারি পরীক্ষা, রোগ নির্ণয় বা প্রেসক্রিপশনের বিকল্প নয়।

Article Summary

Antioxidants are man-made or natural substances that may prevent or delay some types of cell damage. Diets high in vegetables and fruits, which are good sources of antioxidants, have been found to be healthy; however, research has not shown antioxidant supplements to be beneficial in preventing diseases. Examples of antioxidants include vitamins C and E, selenium, and carotenoids, such as beta-carotene, lycopene, lutein, and zeaxanthin....

Key Takeaways

  • This article explains Key Points in simple medical language.
  • This article explains About Free Radicals, Oxidative Stress, and Antioxidants in simple medical language.
  • This article explains Use of Antioxidant Supplements in the United States in simple medical language.
  • This article explains Safety in simple medical language.
Educational health guideWritten for patient understanding and clinical awareness.
Reviewed content workflowUse writer and reviewer profiles for stronger trust.
Emergency safety firstUrgent warning signs are highlighted below.

Seek urgent medical care if you notice

These warning signs are general safety guidance. Local emergency numbers and clinical judgment should always come first.

  • Severe symptoms, breathing difficulty, fainting, confusion, or rapidly worsening illness.
  • New weakness, severe pain, high fever, or symptoms after a serious injury.
  • Any symptom that feels urgent, unusual, or unsafe for the patient.
1

Emergency now

Use emergency care for severe, sudden, rapidly worsening, or life-threatening symptoms.

2

See a doctor

Book a professional medical evaluation if symptoms persist, worsen, recur often, affect daily activities, or occur in a high-risk patient.

3

Learn safely

Use this article to understand possible causes, tests, treatment options, prevention, and questions to ask your clinician.

Antioxidants are man-made or natural substances that may prevent or delay some types of cell damage. Diets high in vegetables and fruits, which are good sources of antioxidants, have been found to be healthy; however, research has not shown antioxidant supplements to be beneficial in preventing diseases. Examples of antioxidants include vitamins C and E, selenium, and carotenoids, such as beta-carotene, lycopene, lutein, and zeaxanthin. This fact sheet provides basic information about antioxidants, summarizes what the science says about antioxidants and health, and suggests sources for additional information.

Key Points

  • Vegetables and fruits are rich sources of antioxidants. There is good evidence that eating a diet that includes plenty of vegetables and fruits is healthy, and official U.S. Government policy urges people to eat more of these foods. Research has shown that people who eat more vegetables and fruits have lower risks of several diseases; however, it is not clear whether these results are related to the number of antioxidants in vegetables and fruits, to other components of these foods, to other factors in people’s diets, or to other lifestyle choices.
  • Rigorous scientific studies involving more than 100,000 people combined have tested whether antioxidant supplements can help prevent chronic diseases, such as cardiovascular diseases, cancer, and cataracts. In most instances, antioxidants did not reduce the risks of developing these diseases.
  • Concerns have not been raised about the safety of antioxidants in food. However, high-dose supplements of antioxidants may be linked to health risks in some cases. Supplementing with high doses of beta-carotene may increase the risk of lung cancer in smokers. Supplementing with high doses of vitamin E may increase the risks of prostate cancer and one type of stroke.
  • Antioxidant supplements may interact with some medicines.
  • Tell all of your health care providers about any complementary and integrative health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

About Free Radicals, Oxidative Stress, and Antioxidants

Free radicals are highly unstable molecules that are naturally formed when you exercise and when your body converts food into energy. Your body can also be exposed to free radicals from a variety of environmental sources, such as cigarette smoke, air pollution, and sunlight. Free radicals can cause “oxidative stress,” a process that can trigger cell damage. Oxidative stress is thought to play a role in a variety of diseases including cancer, cardiovascular diseases, insulin is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।" data-rx-term="diabetes" data-rx-definition="Diabetes is a condition where blood sugar stays too high because insulin is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।">diabetes, Alzheimer’s disease, Parkinson’s disease, and eye diseases such as cataracts and age-related macular degeneration.

Antioxidant molecules have been shown to counteract oxidative stress in laboratory experiments (for example, in cells or animal studies). However, there is debate as to whether consuming large amounts of antioxidants in supplement form actually benefits health. There is also some concern that consuming antioxidant supplements in excessive doses may be harmful.

Vegetables and fruits are healthy foods and rich sources of antioxidants. Official U.S. Government policy urges people to eat more vegetables and fruits. Concerns have not been raised about the safety of any amounts of antioxidants in food. For more information on antioxidants in foods, visit the U.S. Department of Agriculture webpage on antioxidants and phytonutrients.

Use of Antioxidant Supplements in the United States

A 2009 analysis using data from the National Health and Nutrition Examination Survey (1999–2000 and 2001–2002) estimated the amounts of antioxidants adults in the United States get from foods and supplements. Supplements accounted for 54 percent of vitamin C, 64 percent of vitamin E, 14 percent of alpha- and beta-carotene, and 11 percent of selenium intake.

Safety

  • High-dose antioxidant supplements may be harmful in some cases. For example, the results of some studies have linked the use of high-dose beta-carotene supplements to an increased risk of lung cancer in smokers and the use of high-dose vitamin E supplements to increased risks of hemorrhagic stroke (a type of stroke caused by bleeding in the brain) and prostate cancer.
  • Like some other dietary supplements, antioxidant supplements may interact with certain medications. For example, vitamin E supplements may increase the risk of bleeding in people who are taking anticoagulant drugs (“blood thinners”). There is conflicting evidence on the effects of taking antioxidant supplements during cancer treatment; some studies suggest that this may be beneficial, but others suggest that it may be harmful. The National Cancer Institute recommends that people who are being treated for cancer talk with their health care provider before taking supplements.

For more information about the safety of dietary supplements, see the National Center for Complementary and Integrative Health (NCCIH) fact sheet Using Dietary Supplements Wisely.

What the Science Says

Several decades of dietary research findings suggested that consuming greater amounts of antioxidant-rich foods might help to protect against diseases. Because of these results, there has been a lot of research on antioxidant supplements. Rigorous trials of antioxidant supplements in large numbers of people have not found that high doses of antioxidant supplements prevent disease. This section describes the preliminary research findings, the results of the clinical trials, and possible explanations for the differences in study results.

Observational and Laboratory Studies

Observational studies on the typical eating habits, lifestyles, and health histories of large groups of people have shown that those who ate more vegetables and fruits had lower risks of several diseases, including cardiovascular disease, stroke, cancer, and cataracts. Observational studies can provide ideas about possible relationships between dietary or lifestyle factors and disease risk, but they cannot show that one factor causes another because they cannot account for other factors that may be involved. For example, people who eat more antioxidant-rich foods might also be more likely to exercise and less likely to smoke. It may be that these factors, rather than antioxidants, account for their lower disease risk.

Researchers have also studied antioxidants in laboratory experiments. These experiments showed that antioxidants interacted with free radicals and stabilized them, thus preventing the free radicals from causing cell damage.

Clinical Trials of Antioxidants

Because the results of such research seemed very promising, large, long-term studies—many of which were funded by the National Institutes of Health (NIH)—were conducted to test whether antioxidant supplements, when taken for periods of at least a few years, could help prevent diseases such as cardiovascular diseases and cancer in people. In these studies, volunteers were randomly assigned to take either an antioxidant or a placebo (an identical-looking product that did not contain the antioxidant). The research was conducted in a double-blind manner (neither the study participants nor the investigators knew which product was being taken). Studies of this type—called clinical trials—are designed to provide clear answers to specific questions about how a substance affects people’s health.

Among the earliest of these studies were three large NIH-sponsored trials of high-dose supplements of beta-carotene, alone or in combination with other nutrients. These trials, completed in the mid-1990s, all showed that beta-carotene did not protect against cancer or cardiovascular disease. In one trial, beta-carotene supplements increased the risk of lung cancer in smokers, and in another trial, supplements containing both beta-carotene and vitamin A had the same effect.

More recent studies have also found that in most instances antioxidant supplements did not help to prevent disease. For example:

  • The Women’s Health Study, which included almost 40,000 healthy women at least 45 years of age, found that vitamin E supplements did not reduce the risk of heart attack, stroke, cancer, age-related macular degeneration, or cataracts. Although vitamin E supplements were associated with fewer deaths from cardiovascular causes, they did not reduce the overall death rate of study participants.
  • The Women’s Antioxidant Cardiovascular Study found no beneficial effects of vitamin C, vitamin E, or beta-carotene supplements on cardiovascular events (heart attack, stroke, or death from cardiovascular diseases) or the likelihood of developing insulin is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।" data-rx-term="diabetes" data-rx-definition="Diabetes is a condition where blood sugar stays too high because insulin is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।">diabetes or cancer in more than 8,000 female health professionals, aged 40 years or older, who were at high risk for cardiovascular disease. Antioxidant supplements also did not slow changes in cognitive function among women in this study who were aged 65 or older.
  • The Physicians’ Health Study II, which included more than 14,000 male physicians aged 50 or older, found that neither vitamin E nor vitamin C supplements reduced the risk of major cardiovascular events (heart attack, stroke, or death from cardiovascular disease), cancer, or cataracts. In fact, vitamin E supplements were associated with an increased risk of hemorrhagic stroke in this study.
  • The Selenium and Vitamin E Cancer Prevention Trial (SELECT)—a study of more than 35,000 men aged 50 or older—found that selenium and vitamin E supplements, taken alone or together, did not prevent prostate cancer. A 2011 updated analysis from this trial, based on a longer followup period of study participants, concluded that vitamin E supplements increased the occurrence of prostate cancer by 17 percent in men who received the vitamin E supplement alone compared with those who received placebo. There was no increase in prostate cancer when vitamin E and selenium were taken together.

Unlike the studies described above, the Age-Related Eye Disease Study (AREDS), led by the National Eye Institute and cosponsored by other components of NIH, including NCCIH, found a beneficial effect of antioxidant supplements. This study showed that a combination of antioxidants (vitamin C, vitamin E, and beta-carotene) and zinc reduced the risk of developing the advanced stage of age-related macular degeneration by 25 percent in people who had the intermediate stage of this disease or who had the advanced stage in only one eye. Antioxidant supplements used alone reduced the risk by about 17 percent. In the same study, however, antioxidants did not help to prevent cataracts or slow their progression.

  • A followup study, AREDS2, found that adding omega-3 fatty acids (fish oil) to the combination of supplements did not improve its effectiveness. However, adding lutein and zeaxanthin (two carotenoids found in the eye) improved the supplement’s effectiveness in people who were not taking beta-carotene and those who consumed only small amounts of lutein and zeaxanthin in foods.

Why Don’t Antioxidant Supplements Work?

Most clinical studies of antioxidant supplements have not found them to provide substantial health benefits. Researchers have suggested several reasons for this, including the following:

  • The beneficial health effects of a diet high in vegetables and fruits or other antioxidant-rich foods may actually be caused by other substances present in the same foods, other dietary factors, or other lifestyle choices rather than antioxidants.
  • The effects of the large doses of antioxidants used in supplementation studies may be different from those of the smaller amounts of antioxidants consumed in foods.
  • Differences in the chemical composition of antioxidants in foods versus those in supplements may influence their effects. For example, eight chemical forms of vitamin E are present in foods. Vitamin E supplements, on the other hand, typically include only one of these forms—alpha-tocopherol. Alpha-tocopherol also has been used in almost all research studies on vitamin E.
  • For some diseases, specific antioxidants might be more effective than the ones that have been tested. For example, to prevent eye diseases, antioxidants that are present in the eye, such as lutein, might be more beneficial than those that are not found in the eye, such as beta-carotene.
  • The relationship between free radicals and health may be more complex than has previously been thought. Under some circumstances, free radicals actually may be beneficial rather than harmful, and removing them may be undesirable.
  • The antioxidant supplements may not have been given for a long enough time to prevent chronic diseases, such as cardiovascular diseases or cancer, which develop over decades.
  • The participants in the clinical trials discussed above were either members of the general population or people who were at high risk for particular diseases. They were not necessarily under increased oxidative stress. Antioxidants might help to prevent diseases in people who are under increased oxidative stress even if they don’t prevent them in other people.

If You Are Considering Antioxidant Supplements

  • Do not use antioxidant supplements to replace a healthy diet or conventional medical care, or as a reason to postpone seeing a health care provider about a medical problem.
  • If you have age-related macular degeneration, consult your health care providers to determine whether supplements of the type used in the AREDS trial are appropriate for you.
  • If you are considering a dietary supplement, first get information on it from reliable sources. Keep in mind that dietary supplements may interact with medications or other supplements and may contain ingredients not listed on the label. Your health care provider can advise you. If you are pregnant or nursing a child, or if you are considering giving a child a dietary supplement, it is especially important to consult your (or your child’s) health care provider.
  • Tell all of your health care providers about any complementary health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

NCCIH- and NIH-Funded Research

Researchers supported by NCCIH and other components of NIH are conducting a variety of studies using antioxidant supplements.

Topics of recent NCCIH research on antioxidants include:

  • The ways in which two chemical forms of vitamin E affect infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।" data-rx-term="inflammation" data-rx-definition="Inflammation is the body’s response to injury, infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।">inflammation
  • The biological effects of selenium on immune function
  • The effects of a range of doses of alpha-lipoic acid on oxidative stress
  • The effects of alpha-lipoic acid and acetyl-L-carnitine on infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।" data-rx-term="inflammation" data-rx-definition="Inflammation is the body’s response to injury, infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।">inflammation in people with sickle cell disease.

NCCIH also funds a center of excellence for research on antioxidant therapies, which is conducting studies on the effects of antioxidants on various diseases and on aging.

Other components of NIH are also sponsoring research on antioxidants. Recent topics include:

  • The effects of antioxidant therapy in Alzheimer’s disease
  • The roles of oxidation and antioxidants in breast cancer risk
  • Whether antioxidants from a pomegranate can help prevent or treat prostate cancer
  • Whether anthocyanins (a group of antioxidants from berries) can help prevent esophageal cancer.

From Where To Buy

Amazon Best Seller
NOW Supplements, Vitamin C-1,000 with 100 mg of Bioflavonoids, Antioxidant Protection*, 250 Veg Capsules
7,384 Reviews
NOW Supplements, Vitamin C-1,000 with 100 mg of Bioflavonoids, Antioxidant Protection*, 250 Veg Capsules
  • ANTIOXIDANT PROTECTION: NOW offers you this yearly supply of vegetarian/vegan Vitamin C-1000 in a convenient easy to swallow capsule. Did you know Vitamin C is essential for the production of collagen. Vitamin C is important for skin, bone, and joint health as well as for supporting the immune system.
  • Product Note: Exposure to heat or sunlight may lead to melting/damage of product. Hence customers are expected to be available during the product delivery
  • WITH BIOFLAVONOIDS: One capsule a day packed with vitamin C gives you antioxidant protection and 100 mg of bioflavonoids to support your immune system.
  • CLASSIFICATIONS/CERTIFICATIONS: Non-GMO, kosher, soy free, dairy free, egg free, sugar free, nut free, low sodium, made without gluten, vegetarian/vegan
  • GMP Quality Assured: NPA A-rated GMP certification means that every aspect of the NOW manufacturing process has been examined, including our laboratory/testing methods (for stability, potency, and product formulation).
  • Packaged in the USA by a family owned and operated company since 1968.
  • During the summer months products may arrive warm but Amazon stores and ships products in accordance with manufacturers' recommendations, when provided.
$29.99 −$13.50 $16.49 Amazon Prime
Buy Now On Amazon.com Price incl. tax, excl. shipping

or

Amazing Grass Greens Blend Antioxidant: Super Greens Powder Smoothie Mix with Organic Spirulina, Beet Root Powder, Elderberry & Probiotics, Sweet Berry, 60 Servings (Packaging May Vary)
28,204 Reviews
Amazing Grass Greens Blend Antioxidant: Super Greens Powder Smoothie Mix with Organic Spirulina, Beet Root Powder, Elderberry & Probiotics, Sweet Berry, 60 Servings (Packaging May Vary)
  • PROMOTES HEALTHY DIGESTION: Our Greens Blend are thoughtfully crafted with a nutritious blend of alkalizing greens, antioxidants, fiber & pre and probiotics to support your overall digestive health to help you feel amazing.
  • CLEAN AND GREEN: Made with ingredients you can trust, our Greens Blend are Certified Organic by CCOF, Sugar Free, Gluten Free, Plant Based, Kosher and Non GMO.
  • SUPPORTS IMMUNITY AND GUT HEALTH: Packed with 2 full servings of wholesome fruits, vegetables, vitamins & minerals in every scoop, our Greens Blend ensures you are getting the right amount of nutrients to support overall health and immunity.
  • NATURAL ENERGY BOOST: Packed with superfoods, our Greens Blend provides that extra boost to your day. With added probiotics, our Greens Blend promote healthy gut bacteria so you can feel your best!
  • ONE SCOOP A DAY: Whether it is starting your day off on the right foot or for an afternoon pick me up, our Greens Blend are easy to incorporate into your daily routine.
$47.30 Amazon Prime
Buy Now On Amazon.com Price incl. tax, excl. shipping

References

Doctor visit helper

Prepare before seeing a doctor

A simple rural-patient checklist to help you explain symptoms clearly, ask better questions, and avoid unsafe self-treatment.

Safety note: This is not a prescription or diagnosis. For severe symptoms, pregnancy danger signs, children with serious illness, chest pain, breathing difficulty, stroke-like weakness, or major injury, seek urgent care.

Which doctor may help?

Start with a registered doctor or the nearest qualified health center.

What to tell the doctor

  • Write when the problem started and how it changed.
  • Bring old prescriptions, investigation reports, and current medicines.
  • Write allergies, pregnancy status, diabetes, kidney/liver disease, and major past illnesses.
  • Bring one family member if the patient is weak, elderly, confused, or a child.

Questions to ask

  • What is the most likely cause of my symptoms?
  • Which danger signs mean I should go to hospital quickly?
  • Which tests are necessary now, and which can wait?
  • How should I take medicines safely and what side effects should I watch for?
  • When should I come for follow-up?

Tests to discuss

  • Vital signs: temperature, pulse, blood pressure, oxygen saturation
  • Basic physical examination by a clinician
  • CBC, urine test, blood sugar, or imaging only when clinically needed

Avoid these mistakes

  • Do not use antibiotics, steroid tablets/injections, or strong painkillers without proper medical advice.
  • Do not hide pregnancy, kidney disease, ulcer, allergy, or blood thinner use.
  • Do not delay emergency care when danger signs are present.

Medicine safety and first-aid guide

This section is for patient education only. It does not replace a doctor, pharmacist, or emergency care.

Safe first steps

  • Avoid heavy lifting, sudden bending, and prolonged bed rest.
  • Use comfortable posture and gentle movement as tolerated.
  • Discuss physiotherapy, X-ray, or MRI only when clinically needed.

OTC medicine safety

  • For mild back pain, pain-relief medicine may be discussed with a doctor or pharmacist.
  • Avoid repeated painkiller use if you have kidney disease, stomach ulcer, uncontrolled blood pressure, or are taking blood thinners.

Avoid these mistakes

  • Do not start antibiotics without a proper medical decision.
  • Do not use steroid tablets or injections casually for quick relief.
  • Do not delay emergency care because of home remedies.

Get urgent help if

  • Back pain with leg weakness, numbness around private area, loss of urine/stool control, fever, cancer history, or major injury needs urgent care.
Medicine names, dose, and timing must be decided by a qualified clinician or pharmacist after checking age, pregnancy, allergy, other diseases, and current medicines.

For rural patients and family caregivers

Patient health record and symptom diary

Write your symptoms, medicines already taken, test results, and questions before visiting a doctor. This note stays on your device unless you print or copy it.

Doctor to discuss: Doctor / qualified healthcare provider
Tests to discuss with doctor
  • Basic vital signs: temperature, pulse, blood pressure, oxygen level if needed
  • Relevant blood, urine, imaging, or specialist tests only after clinical assessment
Questions to ask
  • What is the most likely cause of my symptoms?
  • Which warning signs mean I should go to emergency care?
  • Which tests are really needed now?
  • Which medicines are safe for my age, pregnancy status, allergy, kidney/liver/stomach condition, and current medicines?

Emergency warning signs such as chest pain, severe breathing difficulty, sudden weakness, confusion, severe dehydration, major injury, or loss of bladder/bowel control need urgent medical care. Do not wait for online information.

Safe pathway to proper treatment

Care roadmap for: What Is Antioxidants? – Types, Health Benefits

Use this simple roadmap to understand the next safe steps. It is educational and does not replace examination by a doctor.

Go to emergency care if you notice:
  • Severe or rapidly worsening symptoms
  • Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration
Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.
  1. Step 1

    Check danger signs first

    If danger signs are present, seek emergency care and do not wait for online information.

  2. Step 2

    Record the symptom story

    Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.

  3. Step 3

    Visit a qualified clinician

    A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.

  4. Step 4

    Do only useful tests

    Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.

  5. Step 5

    Follow up and return early if worse

    If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips
  • Take a written symptom diary and all previous prescriptions/test reports.
  • Do not hide medicines already taken, even herbal or over-the-counter medicines.
  • Ask which warning signs mean urgent referral to hospital.

This roadmap is for education. A real diagnosis and treatment plan requires history, examination, and clinical judgment.

RX Patient Help

Ask a health question safely

Write your symptom story. A health professional or site editor can review it before any answer is prepared. This box is not for emergency care.

Emergency first: Severe chest pain, breathing trouble, unconsciousness, stroke signs, severe injury, heavy bleeding, or rapidly worsening symptoms need urgent local medical care now.

Frequently Asked Questions

Key PointsVegetables and fruits are rich sources of antioxidants. There is good evidence that eating a diet that includes plenty of vegetables and fruits is healthy, and official U.S. Government policy urges people to eat more of these foods. Research has shown that people who eat more vegetables and fruits have lower risks of several diseases; however, it is not clear whether these results are related to the number of antioxidants in vegetables and fruits, to other components of these foods, to other factors in people’s diets, or to other lifestyle choices. Rigorous scientific studies involving more than 100,000 people combined have tested whether antioxidant supplements can help prevent chronic diseases, such as cardiovascular diseases, cancer, and cataracts. In most instances, antioxidants did not reduce the risks of developing these diseases. Concerns have not been raised about the safety of antioxidants in food. However, high-dose supplements of antioxidants may be linked to health risks in some cases. Supplementing with high doses of beta-carotene may increase the risk of lung cancer in smokers. Supplementing with high doses of vitamin E may increase the risks of prostate cancer and one type of stroke. Antioxidant supplements may interact with some medicines. Tell all of your health care providers about any complementary and integrative health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.About Free Radicals, Oxidative Stress, and AntioxidantsFree radicals are highly unstable molecules that are naturally formed when you exercise and when your body converts food into energy. Your body can also be exposed to free radicals from a variety of environmental sources, such as cigarette smoke, air pollution, and sunlight. Free radicals can cause “oxidative stress,” a process that can trigger cell damage. Oxidative stress is thought to play a role in a variety of diseases including cancer, cardiovascular diseases, diabetes, Alzheimer’s disease, Parkinson’s disease, and eye diseases such as cataracts and age-related macular degeneration.Antioxidant molecules have been shown to counteract oxidative stress in laboratory experiments (for example, in cells or animal studies). However, there is debate as to whether consuming large amounts of antioxidants in supplement form actually benefits health. There is also some concern that consuming antioxidant supplements in excessive doses may be harmful.Vegetables and fruits are healthy foods and rich sources of antioxidants. Official U.S. Government policy urges people to eat more vegetables and fruits. Concerns have not been raised about the safety of any amounts of antioxidants in food. For more information on antioxidants in foods, visit the U.S. Department of Agriculture webpage on antioxidants and phytonutrients.Use of Antioxidant Supplements in the United StatesA 2009 analysis using data from the National Health and Nutrition Examination Survey (1999–2000 and 2001–2002) estimated the amounts of antioxidants adults in the United States get from foods and supplements. Supplements accounted for 54 percent of vitamin C, 64 percent of vitamin E, 14 percent of alpha- and beta-carotene, and 11 percent of selenium intake.SafetyHigh-dose antioxidant supplements may be harmful in some cases. For example, the results of some studies have linked the use of high-dose beta-carotene supplements to an increased risk of lung cancer in smokers and the use of high-dose vitamin E supplements to increased risks of hemorrhagic stroke (a type of stroke caused by bleeding in the brain) and prostate cancer. Like some other dietary supplements, antioxidant supplements may interact with certain medications. For example, vitamin E supplements may increase the risk of bleeding in people who are taking anticoagulant drugs (“blood thinners”). There is conflicting evidence on the effects of taking antioxidant supplements during cancer treatment; some studies suggest that this may be beneficial, but others suggest that it may be harmful. The National Cancer Institute recommends that people who are being treated for cancer talk with their health care provider before taking supplements.For more information about the safety of dietary supplements, see the National Center for Complementary and Integrative Health (NCCIH) fact sheet Using Dietary Supplements Wisely.What the Science SaysSeveral decades of dietary research findings suggested that consuming greater amounts of antioxidant-rich foods might help to protect against diseases. Because of these results, there has been a lot of research on antioxidant supplements. Rigorous trials of antioxidant supplements in large numbers of people have not found that high doses of antioxidant supplements prevent disease. This section describes the preliminary research findings, the results of the clinical trials, and possible explanations for the differences in study results. Observational and Laboratory Studies Observational studies on the typical eating habits, lifestyles, and health histories of large groups of people have shown that those who ate more vegetables and fruits had lower risks of several diseases, including cardiovascular disease, stroke, cancer, and cataracts. Observational studies can provide ideas about possible relationships between dietary or lifestyle factors and disease risk, but they cannot show that one factor causes another because they cannot account for other factors that may be involved. For example, people who eat more antioxidant-rich foods might also be more likely to exercise and less likely to smoke. It may be that these factors, rather than antioxidants, account for their lower disease risk.Researchers have also studied antioxidants in laboratory experiments. These experiments showed that antioxidants interacted with free radicals and stabilized them, thus preventing the free radicals from causing cell damage. Clinical Trials of Antioxidants Because the results of such research seemed very promising, large, long-term studies—many of which were funded by the National Institutes of Health (NIH)—were conducted to test whether antioxidant supplements, when taken for periods of at least a few years, could help prevent diseases such as cardiovascular diseases and cancer in people. In these studies, volunteers were randomly assigned to take either an antioxidant or a placebo (an identical-looking product that did not contain the antioxidant). The research was conducted in a double-blind manner (neither the study participants nor the investigators knew which product was being taken). Studies of this type—called clinical trials—are designed to provide clear answers to specific questions about how a substance affects people’s health.Among the earliest of these studies were three large NIH-sponsored trials of high-dose supplements of beta-carotene, alone or in combination with other nutrients. These trials, completed in the mid-1990s, all showed that beta-carotene did not protect against cancer or cardiovascular disease. In one trial, beta-carotene supplements increased the risk of lung cancer in smokers, and in another trial, supplements containing both beta-carotene and vitamin A had the same effect.More recent studies have also found that in most instances antioxidant supplements did not help to prevent disease. For example:The Women’s Health Study, which included almost 40,000 healthy women at least 45 years of age, found that vitamin E supplements did not reduce the risk of heart attack, stroke, cancer, age-related macular degeneration, or cataracts. Although vitamin E supplements were associated with fewer deaths from cardiovascular causes, they did not reduce the overall death rate of study participants. The Women’s Antioxidant Cardiovascular Study found no beneficial effects of vitamin C, vitamin E, or beta-carotene supplements on cardiovascular events (heart attack, stroke, or death from cardiovascular diseases) or the likelihood of developing diabetes or cancer in more than 8,000 female health professionals, aged 40 years or older, who were at high risk for cardiovascular disease. Antioxidant supplements also did not slow changes in cognitive function among women in this study who were aged 65 or older. The Physicians’ Health Study II, which included more than 14,000 male physicians aged 50 or older, found that neither vitamin E nor vitamin C supplements reduced the risk of major cardiovascular events (heart attack, stroke, or death from cardiovascular disease), cancer, or cataracts. In fact, vitamin E supplements were associated with an increased risk of hemorrhagic stroke in this study. The Selenium and Vitamin E Cancer Prevention Trial (SELECT)—a study of more than 35,000 men aged 50 or older—found that selenium and vitamin E supplements, taken alone or together, did not prevent prostate cancer. A 2011 updated analysis from this trial, based on a longer followup period of study participants, concluded that vitamin E supplements increased the occurrence of prostate cancer by 17 percent in men who received the vitamin E supplement alone compared with those who received placebo. There was no increase in prostate cancer when vitamin E and selenium were taken together.Unlike the studies described above, the Age-Related Eye Disease Study (AREDS), led by the National Eye Institute and cosponsored by other components of NIH, including NCCIH, found a beneficial effect of antioxidant supplements. This study showed that a combination of antioxidants (vitamin C, vitamin E, and beta-carotene) and zinc reduced the risk of developing the advanced stage of age-related macular degeneration by 25 percent in people who had the intermediate stage of this disease or who had the advanced stage in only one eye. Antioxidant supplements used alone reduced the risk by about 17 percent. In the same study, however, antioxidants did not help to prevent cataracts or slow their progression.A followup study, AREDS2, found that adding omega-3 fatty acids (fish oil) to the combination of supplements did not improve its effectiveness. However, adding lutein and zeaxanthin (two carotenoids found in the eye) improved the supplement’s effectiveness in people who were not taking beta-carotene and those who consumed only small amounts of lutein and zeaxanthin in foods.Why Don’t Antioxidant Supplements Work?

Most clinical studies of antioxidant supplements have not found them to provide substantial health benefits. Researchers have suggested several reasons for this, including the following: The beneficial health effects of a diet high in vegetables and fruits or other antioxidant-rich foods may actually be caused by other substances present in the same foods, other dietary factors, or other lifestyle choices rather than antioxidants. The effects of the large doses of antioxidants used in supplementation studies may be different from those…

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area from the RX Article Professional Blocks panel.

More from this topic
  1. How to Reset Your Body from Chronic Stress?

    Chronic? stress isn’t something that arrives very loudly. It builds very slowly — and tight shoulders, having poor sleep, feeling constantly fatigue?, feeling irritable, or just...

    April 7, 2026 • Top Global News
  2. Congenital Amegakaryocytic Thrombocytopenia Type 1 (CAMT-1)

    Congenital? amegakaryocytic thrombocytopenia? type 1 (CAMT-1) is a very rare inherited blood disease present from birth. In this condition the body cannot produce enough platelets, which...

    March 9, 2026 • Top Global News
  3. Blue Cone Monochromacy (BCM)

    Blue cone monochromacy (BCM) is a very rare eye disease that a person is born with. In this condition, the red and green cone cells in...

    March 3, 2026 • Top Global News
  4. Is it Okay to Cry in Front of a Psychiatrist?

    Is It Okay to Cry During a Psychiatric Session? To speak with all honesty – yes. It is truly okay to cry in front of a...

    February 17, 2026 • Top Global News
  5. Autosomal Dominant Demyelinating Charcot-Marie-Tooth Disease

    Autosomal dominant demyelinating Charcot-Marie-Tooth disease is a long-term nerve disease that mainly damages the peripheral nerves, which are the nerves outside the brain and spinal cord....

    January 6, 2026 • Top Global News
  6. F5-Related Budd–Chiari Syndrome (Factor V Leiden–Related Hepatic Vein Thrombosis)

    F5-related Budd–Chiari syndrome means Budd–Chiari syndrome (BCS) that happens in a person who carries the Factor V Leiden (F5 G1691A) mutation. In BCS, blood cannot leave...

    November 5, 2025 • Top Global News
  7. Beckwith–Wiedemann Syndrome (BWS)

    Beckwith–Wiedemann syndrome (BWS) is a genetic growth disorder that starts before birth. Babies are often large, the tongue may be big, some organs are enlarged, and...

    October 20, 2025 • Top Global News
  8. Micromelic Dysplasia–Dislocation of Radius Syndrome

    Micromelic dysplasia–dislocation of radius syndrome is a rare genetic bone growth disorder. “Micromelic” means the arms and legs are short from birth. “Dislocation of radius” means...

    October 12, 2025 • Top Global News
  9. Health Risks of a Sedentary Lifestyle and How to Make Changes

    Today’s fast-paced in the passive world, a sedentary lifestyle is quietly damaging both our body and mind. For a long time on a desk, dependence on...

    October 3, 2025 • Top Global News
  10. Oligodendroglioma

    Oligodendroglioma is a primary brain tumor that grows from glial cells called oligodendrocytes, which normally make myelin—the “insulation” around nerve fibers. In the modern World Health...

    September 17, 2025 • Top Global News