American Health & Medical Research Association
Comparison guide

Vitamin pills mostly failed big prevention trials, though a few still earn their place

Nutrients in food arrive with fiber, partner compounds and modest doses. Isolated pills often disappointed in big trials, yet folic acid, vitamin B12, vitamin D and iron do clear jobs for specific people.

By the Health Research USA editorial team

Published Last updated October 2026

Written from the sources listed below; links checked October 2026. It touches on medicines, doses or health conditions and has not yet been reviewed by a licensed clinician, so use it to prepare for a conversation with yours. How we research and review

Sources14, listed below Reading time15 minutes

Where the evidence stands

  • Strong evidence FolateVitamin B12Folic acid before pregnancy helps prevent neural tube defectsB12 from fortified foods or pills helps adults over 50
  • Promising but early Nutrients from food protect better than the same nutrients from pillsCocoa flavanol extract lowers cardiovascular deaths
  • Not enough evidence CalciumMultivitamins prevent heart disease or cancerCalcium pills raise heart risk
  • Evidence says no, or unsafe Vitamin D pills prevent cancer or heart disease in healthy adultsBeta-carotene or vitamin E pills prevent disease

Each use is rated separately, from the scorecard in this guide. Safety cautions are spelled out in the guide itself. How we grade

On this page
  1. Diet studies and pill trials answer different questions
  2. When pills were tested against placebos, most came up short
  3. Why a nutrient can act differently in food and in a pill
  4. Where a supplement does a job food can't easily do
  5. Food first, supplement when: a nutrient-by-nutrient guide
  6. How strong is the evidence?
  7. Food first fits natural-health values, and the new guidelines agree
  8. Questions readers ask
  9. The bottom line

Key takeaways

  • In the VITAL trial, nearly 26,000 U.S. adults took 2,000 IU of vitamin D a day or a placebo for about five years, and invasive cancers (793 vs. 824) and major heart events (396 vs. 409) came out about even2.
  • In 2022, the U.S. Preventive Services Task Force found too little evidence to recommend multivitamins for preventing heart disease or cancer, and it advised against beta-carotene and vitamin E7.
  • Food isn’t always the better source: folic acid, the form in pills and fortified grains, is absorbed far better than the folate in leafy greens and beans12.
  • Supplements do clear jobs for some people, including folic acid for anyone who could become pregnant, vitamin B12 after 50 and vitamin D for breastfed babies31213.
  • Start with food, add a supplement only for a named reason, and check each dose against its upper limit.

In November 2018, a team led by JoAnn Manson reported the results of a vitamin D trial that one outside cardiologist called the most definitive to date1.

The trial, called VITAL, randomly assigned nearly 26,000 U.S. adults, men 50 and older and women 55 and older, to take 2,000 IU of vitamin D3 a day or a dummy pill12. After about five years, 793 people in the vitamin D group had been diagnosed with invasive cancer, compared with 824 on placebo2. Major heart events were close to even, too: 396 versus 4092.

Now picture a breastfed newborn. The Dietary Guidelines for Americans, 2025–2030, released in January 2026, say that baby should get a 400 IU vitamin D supplement every day, starting shortly after birth3. In national survey data from 2009 to 2016, only 20.5% of breastfed infants got that much, according to NIH’s Office of Dietary Supplements (ODS)4.

Same vitamin, opposite verdicts. What made the difference was who took it and what they were missing.

For most healthy adults, food does things pills haven’t matched in trials. For specific people at specific times, a supplement does a job food can’t easily do.

Diet studies and pill trials answer different questions

Much of what we know about food and health comes from observational studies. Researchers track what people already eat and see who stays healthy. Supplement trials work differently. They assign pills at random, so the groups start out alike.

People who take supplements tend to differ from people who don’t. According to ODS, people who reach for a multivitamin often eat a more nutrient-rich diet to begin with, even before the pill5. If they also stay healthier, the pill may get credit the plate deserves.

A blood test can mislead in a similar way. When VITAL came out, Erin Michos, a Johns Hopkins cardiologist who wasn’t involved, suggested that low vitamin D might simply mark a person in poorer overall health1. Raising the number with a pill doesn’t fix whatever caused it.

A 2019 Tufts-led study of nearly 31,000 U.S. adults, described in our article on correlation and causation, found that several nutrients tracked with longer life only when they came from food6. It also found that people whose supplements supplied 1,000 mg or more of calcium a day had a higher risk of dying of cancer, but high calcium intakes from meals carried no such signal6.

That study was observational and built on people’s own reports, and the authors warned that other differences could explain some results6.

When pills were tested against placebos, most came up short

Randomized trials are the fairest test of whether a pill prevents disease. In 2022, the U.S. Preventive Services Task Force (USPSTF), an independent panel of experts, weighed them for heart disease and cancer7. It counted 32 trials of vitamin D, 9 of multivitamins, 9 of vitamin E and 6 of beta-carotene, among others7.

  • Beta-carotene. In trials of smokers and people exposed to asbestos at work, beta-carotene pills raised the risk of lung cancer7. One of them, known as ATBC, enrolled male smokers in Finland57. Our articles on fruits and vegetables and on supplement stacks give the numbers.
  • Vitamin e. It didn’t lower deaths, heart disease or cancer7. Two trials linked daily doses of 111 IU and 200 IU to more strokes caused by bleeding7. Our supplement stack article covers SELECT, the large trial of vitamin E and prostate cancer.
  • Vitamin d. Pooled trials showed no difference in overall deaths or in cancer deaths7. The two biggest trials, VITAL and one called D-Health, pointed in opposite directions on cancer deaths7. A 2022 VITAL report found no drop in fractures, either4.
  • Multivitamins. In PHS II, a trial of male doctors, a daily multivitamin cut total cancer by a modest 8% but didn’t reduce heart events5. In a newer trial called COSMOS, a multivitamin didn’t lower total cancer or heart events5.

The task force recommended against beta-carotene and vitamin E for prevention. It found too little evidence to judge most other vitamins, minerals and multivitamins7. Its advice covers healthy adults living at home who aren’t pregnant and don’t have a known deficiency7.

One pill showed a hint of benefit. COSMOS also tested a cocoa flavanol extract in more than 21,000 adults for about 3.6 years8. Cardiovascular deaths were 27% lower, a secondary finding, while the main measure, total heart events, didn’t fall significantly8.

Weigh who paid. Alongside NIH grants, Mars Edge, a nutrition unit of Mars, Inc., gave an investigator-initiated grant and donated the cocoa capsules; Pfizer Consumer Healthcare partly supplied the multivitamins8. According to the hospital’s release, the companies stayed out of the trial’s design, its conduct, the data analysis and the writing8.

Why a nutrient can act differently in food and in a pill

No one has proved why diet studies so often look better than pill trials, but four explanations fit.

Dose. Pills often deliver far more than a plate does. The harms from beta-carotene showed up at 20 and 30 mg a day7. Your gut also has limits. People absorb about 36% of a 300 mg calcium dose but only 28% of a 1,000 mg dose9. For vitamin B12, the share absorbed falls to about 2% of a 500 mcg pill10.

Partners on the plate. Food changes how nutrients are absorbed, in both directions. Plant iron gets a boost from a vitamin C food or a bit of meat or fish on the same plate, but compounds called phytates (in grains and beans) and some polyphenols hold it back11. As a result, ODS estimates that a vegetarian diet yields 5% to 12% of its iron, versus 14% to 18% for a mixed diet11.

One compound versus a package. A pill isolates one nutrient, while a carrot or a bowl of beans brings fiber and many other plant compounds.

Too much of a good thing. Pills can push intakes past safe limits. In a large study of adults 45 and older in Los Angeles and Hawaii, 48% to 61% of multivitamin users took in too much niacin5. And vitamin D poisoning almost always comes from supplements, not from food or sunshine4.

Calcium shows how tangled this gets. Some studies tied calcium pills to more heart disease, while others found no link9. A panel from the National Osteoporosis Foundation and the American Society for Preventive Cardiology concluded that calcium from food or supplements neither raises nor lowers heart risk9. ODS adds that intakes within the upper limit are considered safe for the heart9.

Where a supplement does a job food can’t easily do

Food first doesn’t mean food only. Sometimes a supplement or fortified food is the better tool.

Folic acid before pregnancy. Here the lab-made form wins. At least 85% of folic acid is available to the body when taken with a meal, compared with roughly 50% of the folate in food itself12. Since the FDA required folic acid in enriched grains in 1998, U.S. rates of neural tube defects, which affect the developing spine and brain, have fallen12. Our vitamins and minerals guide has the numbers.

The USPSTF advises anyone who could become pregnant to take 400 to 800 mcg a day, starting at least a month before conception12. Our article on natural versus synthetic vitamins looks at this case in depth.

Vitamin B12 after 50, on a vegan diet or with certain drugs. For adults past 50, ODS points to fortified foods and supplements as the main B12 source, since most can absorb those forms13. B12 occurs naturally only in animal foods, so vegans should rely on fortified foods or a supplement10. Metformin and acid-reducing drugs can also lower B12 levels10.

Vitamin D for babies and some adults. Few foods naturally contain vitamin D4. Beyond breastfed infants, the Endocrine Society, a medical group for hormone specialists, advises vitamin D supplements for children and teens ages 1 to 18, pregnant women, adults with prediabetes and adults 75 and older4. It doesn’t advise routine supplements for healthy adults ages 19 to 744.

Iron for a diagnosed shortfall. ODS reports that iron supplements lower the risk of iron deficiency anemia in pregnancy11. The USPSTF, though, found the evidence too thin to judge routine iron pills for pregnant women without symptoms, and ODS cautions that routine iron may cause harm in pregnant women whose stores are already full1114. Outside pregnancy, shortfalls are more common after heavy periods or frequent blood donation, and with some digestive or heart conditions11.

Get tested first. Hemochromatosis, an inherited condition, makes the body store too much iron. The American Association for the Study of Liver Diseases advises people who have it to avoid iron and vitamin C supplements11.

Prenatal vitamins. In national survey data from 2001 to 2014, about 70% of pregnant women in the U.S. took a supplement14. The new Dietary Guidelines advise talking with your clinician about a daily prenatal vitamin3. Check the label for iodine. The American Thyroid Association advises 150 mcg a day in pregnancy, yet in a 2021 analysis about a quarter of 188 U.S. prenatal products contained none14.

Food first, supplement when: a nutrient-by-nutrient guide

Food amounts and upper limits come from ODS fact sheets updated from 2023 to 2026. Their intake numbers come from the Dietary Reference Intakes set by the National Academies’ Food and Nutrition Board; the B12 values, for example, date from a 1998 report10. An upper limit is the most a healthy adult can take daily without likely harm.

Nutrient Food first Supplement when Evidence for that use Upper-limit caution
Folate Boiled spinach, ½ cup: 131 mcg DFE; black-eyed peas, ½ cup: 105 mcg DFE12 You could become pregnant: 400–800 mcg folic acid a day12 Strong evidence 1,000 mcg a day of folic acid from pills and fortified foods; no limit for food folate12
Vitamin B12 Cooked salmon, 3 oz: 2.6 mcg; fortified nutritional yeast, ¼ cup: 8.3–24 mcg; egg: 0.5 mcg10 You’re over 50 or vegan, or you take metformin or acid reducers1013 Strong evidence None set, because toxicity risk is low10
Vitamin D Farmed rainbow trout, 3 oz: 645 IU; UV-exposed mushrooms, ½ cup: 366 IU; cod liver oil, 1 tbsp: 1,360 IU4 Breastfed infants: 400 IU a day. The Endocrine Society also names ages 1–18, pregnancy, prediabetes and age 75 and up34 Official advice for breastfed infants; evidence says no for preventing cancer or heart disease in healthy adults23 4,000 IU a day for adults; poisoning almost always comes from pills4
Iron Canned white beans, 1 cup: 8 mg; boiled lentils, ½ cup: 3 mg; eat with a vitamin C food11 Diagnosed deficiency, pregnancy or heavy periods, as your clinician advises11 ODS says it lowers anemia risk in pregnancy; the USPSTF calls evidence for routine use without symptoms insufficient1114 45 mg a day; doses that high can upset your stomach; avoid with hemochromatosis11
Calcium Sardines with bones, 3 oz: 325 mg; fortified soymilk, 1 cup: 299 mg; canned salmon with bones, 3 oz: 181 mg9 Food falls short; keep each dose at 500 mg or under, apart from iron pills911 Not enough evidence on heart risk either way9 2,500 mg a day through age 50; 2,000 mg after9

Two cautions. Clinicians sometimes prescribe more than an upper limit for a diagnosed problem, such as iron for anemia11. Stacking products can also push you past a limit; our supplement stack article shows how to check.

How strong is the evidence?

Claim Rating Why
Folic acid before pregnancy helps prevent neural tube defects Strong evidence USPSTF recommends it; defects fell after fortification12
B12 from fortified foods or pills helps adults over 50 Strong evidence ODS advises it; an age-related stomach condition can block food B12, but pills and fortified foods are usually absorbed1013
Nutrients from food protect better than the same nutrients from pills Promising but early One large observational study pointed this way; it can’t prove cause6
Cocoa flavanol extract lowers cardiovascular deaths Promising but early A secondary finding in one trial with industry support8
Multivitamins prevent heart disease or cancer Not enough evidence USPSTF found the evidence insufficient; PHS II saw a small cancer drop, COSMOS none57
Calcium pills raise heart risk Not enough evidence Studies conflict; an expert panel found no effect within the upper limit9
Vitamin D pills prevent cancer or heart disease in healthy adults Evidence says no, or unsafe The largest trial, VITAL, found no reduction, though the USPSTF rates the overall evidence as too thin to judge27
Beta-carotene or vitamin E pills prevent disease Evidence says no, or unsafe USPSTF advises against both; trials found more lung cancer and bleeding strokes7

Food first fits natural-health values, and the new guidelines agree

If you see food as your first medicine and pills as a backup, the research mostly backs that order. Whole foods bring nutrients in everyday amounts, plus partners that pills leave behind.

The Dietary Guidelines for Americans, 2025–2030, point the same way, with exceptions for real needs. For older adults, they say: “When dietary intake or absorption is insufficient, fortified foods or supplements may be needed under medical supervision”3. They tell vegetarians and vegans to check their iron, B12, vitamin D, calcium and iodine from time to time, and to rely on targeted supplements to avoid gaps3.

A supplement maker’s research deserves the same scrutiny as a drug company’s, which is why funding notes like COSMOS’s matter.

Money counts, too. A pill you don’t need is money you could spend on food you do, and our article on supplement math compares products by cost per dose.

When to check with a clinician. Talk to your clinician before you start iron, take vitamin D above the upper limit, or add any supplement during pregnancy. People on metformin or acid-reducing drugs should ask whether their B12 needs checking10. If a supplement seems to cause a problem, stop it and get medical advice. Our companion article on what supplements are explains how to report a reaction to the FDA.

Questions readers ask

Is a daily multivitamin good insurance?

It can help when your diet falls short, ODS says5. But users often eat better to begin with, and multivitamins can push some nutrients past their limits5. For preventing heart disease or cancer, the USPSTF found the evidence insufficient7.

Are synthetic vitamins worse than the ones in food?

Not always. Folic acid is absorbed better than food folate12. And for adults past 50, ODS favors the B12 in pills and fortified foods as the main source13. Judge the form, the dose and the evidence, not the word “natural.”

Should I get my vitamin D level tested?

For healthy people, the Endocrine Society doesn’t advise routine testing4. Ask your clinician whether a test makes sense for you.

Does dark chocolate count as a cocoa flavanol supplement?

No. Researcher JoAnn Manson stressed that COSMOS tested a cocoa extract capsule, not chocolate8. Her colleague Howard Sesso suggested getting flavanols from a balanced diet that includes foods naturally rich in them8.

I eat a vegan diet. Which supplements matter most?

Start with B12. Plants don’t supply it naturally, so a fortified food or a pill has to10. The new guidelines name five nutrients for plant-based eaters to monitor: iron, B12, vitamin D, calcium and iodine3. Iron deserves extra care, since plant iron is harder to absorb and vegetarians need considerably more of it than meat eaters do11.

The bottom line

For most healthy adults, food has done things that isolated vitamin pills haven’t matched in large trials, and a few pills caused harm. Diet studies and pill trials ask different questions, so a nutrient that looks protective on the plate may do little in a capsule.

Supplements still earn their place for named jobs: folic acid for anyone who could become pregnant, B12 after 50 or on a vegan diet, vitamin D for breastfed babies, and iron for a confirmed shortfall. Start with food, choose pills on purpose, and keep every dose under its upper limit unless a clinician says otherwise.

About this article

This article was researched using NIH Office of Dietary Supplements fact sheets, the 2025–2030 Dietary Guidelines, a U.S. Preventive Services Task Force recommendation, randomized trial reports, university and hospital news releases and a science news report, all listed below. It was reviewed in October 2026. It is general education and not medical, legal or financial advice..

Sources

  1. Science News. “Vitamin D Supplements Don’t Prevent Heart Disease or Cancer.” November 2018. sciencenews.org
  2. Manson JE, Cook NR, Lee IM, et al. “Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease.” New England Journal of Medicine, 2019;380(1):33–44. Abstract via University of Arizona. airways.arizona.edu
  3. U.S. Department of Agriculture and U.S. Department of Health and Human Services. “Dietary Guidelines for Americans, 2025–2030.” January 2026. cdn.realfood.gov
  4. NIH Office of Dietary Supplements. “Vitamin D: Fact Sheet for Health Professionals.” National Institutes of Health, accessed October 2026. ods.od.nih.gov
  5. NIH Office of Dietary Supplements. “Multivitamin/mineral Supplements: Fact Sheet for Health Professionals.” National Institutes of Health, updated July 17, 2024. ods.od.nih.gov
  6. Tufts University (news release via Newswise). “Nutrients From Food, Not Supplements, Linked to Lower Risks of Death, Cancer” (on Chen F, Du M, Blumberg JB, et al., Annals of Internal Medicine, 2019, doi:10.7326/M18-2478). April 8, 2019. newswise.com (study abstract, with sample size of 30,899, reproduced by France’s Institut national du cancer: cancer.fr)
  7. U.S. Preventive Services Task Force. “Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: US Preventive Services Task Force Recommendation Statement.” JAMA, 2022;327(23):2326–2333. uspreventiveservicestaskforce.org
  8. Brigham and Women’s Hospital (news release via ScienceDaily). “Trial Testing Cocoa Flavanol Supplement Shows Promise for Reducing Cardiovascular Risk” (on Sesso HD et al., American Journal of Clinical Nutrition, 2022, doi:10.1093/ajcn/nqac055). March 16, 2022. sciencedaily.com
  9. NIH Office of Dietary Supplements. “Calcium: Fact Sheet for Health Professionals.” National Institutes of Health, accessed October 2026. ods.od.nih.gov
  10. NIH Office of Dietary Supplements. “Vitamin B12: Fact Sheet for Health Professionals.” National Institutes of Health, updated July 2, 2025. ods.od.nih.gov
  11. NIH Office of Dietary Supplements. “Iron: Fact Sheet for Health Professionals.” National Institutes of Health, updated September 4, 2025. ods.od.nih.gov
  12. NIH Office of Dietary Supplements. “Folate: Fact Sheet for Health Professionals.” National Institutes of Health, accessed October 2026. ods.od.nih.gov
  13. NIH Office of Dietary Supplements. “Vitamin B12: Fact Sheet for Consumers.” National Institutes of Health, updated December 15, 2023. ods.od.nih.gov
  14. NIH Office of Dietary Supplements. “Dietary Supplements and Life Stages: Pregnancy: Fact Sheet for Health Professionals.” National Institutes of Health, accessed October 2026. ods.od.nih.gov