Everyday supplements for adults: what the research says about Omega-3 fatty acids, Vitamin D, Protein supplements

What people try

3Omega-3 fatty acidsStage 3 · Large studies in people · Food, supplements and a prescription formMost research has focused on two omega-3s called EPA and DHA.Main risk: The pages say side effects are usually mild, such as unpleasant taste, bad breath, heartburn, nausea, and diarrhea.3Vitamin DStage 3 · Large studies in people · Over-the-counter supplementVitamin D is a fat-soluble vitamin found in a few foods, added to others, sold as a supplement, and made by skin in sunlight.Main risk: Blood levels above 125 nmol/L (50 ng/mL) can be linked to harmful effects.3Protein supplementsStage 3 · Large studies in people · Over-the-counter supplementProtein is one of the more common ingredients in supplements sold to improve exercise and athletic performance.Main risk: The page says high protein intakes seem quite safe, but more than the recommended amounts gives no benefit.3CalciumStage 3 · Large studies in people · Over-the-counter supplementCalcium is a mineral your body needs to build and maintain strong bones and to carry out many important functions.Main risk: Some research suggests that high calcium intakes might increase the risk of heart disease and prostate cancer.2CreatineStage 2 · Small studies in people · Over-the-counter supplementCreatine is a compound stored in your muscles that supplies them with energy.Main risk: Creatine can cause weight gain because it tends to make the body hold water, but it is otherwise considered safe for healthy adults.2MultivitaminsStage 2 · Small studies in people · Over-the-counter supplementMultivitamin/mineral supplements combine several vitamins and minerals, and sometimes other ingredients, in one product.Main risk: Taking a multivitamin can raise the chance of getting too much of some nutrients, such as iron, vitamin A, zinc, niacin and folic acid.2Fiber supplementsStage 2 · Small studies in people · Over-the-counter supplementPsyllium is a bulk-forming fiber laxative used to treat constipation.Main risk: Psyllium powder accidentally breathed in while mixing a dose can cause allergic reactions.2MagnesiumStage 2 · Small studies in people · Over-the-counter supplementMagnesium is a mineral the body needs, found in foods, supplements, and some medicines such as antacids and laxatives.Main risk: High doses from supplements or medicines often cause diarrhea, which can come with nausea and belly cramping.2Vitamin B12Stage 2 · Small studies in people · Over-the-counter supplement; injections by prescriptionVitamin B12 is a nutrient that helps keep blood and nerve cells healthy and helps make DNA.Main risk: The pages stress that vitamin B12 is generally considered safe, even at high doses, because the body does not store excess amounts.

Products

Sorted by the best research stage of each product's ingredients, then by price. The stage describes research on the ingredient, not proof that the product works.

Supplements 50

Recent research

Summary of earlier studies

Eye supplements that target aging pathways: a review of current evidence

This review looked at vitamins and similar products for eye diseases tied to aging.

New trial

Testing creatine and HMB with home exercise for muscle loss in Huntington's disease

Researchers plan to compare creatine, HMB, both together, and a placebo, with all groups doing home exercise.

Study in 27 cardiac rehabilitation patients in a randomized trial

Whey protein and vitamin D may lower some inflammation markers in heart rehab patients

Heart rehab patients took a whey protein and vitamin D drink for two weeks, and some inflammation markers dropped.

New trial

Creatine and walking football for older adults in Madrid: a planned study

This is a planned study that has not started recruiting people yet.

Study in 61 older men in a randomized trial, four weeks

Protein and leucine add-ons did not beat diet alone for older men losing weight

Sixty-one older men followed a fasting diet for four weeks and took protein, leucine, or a placebo.

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What others are writing

Recent articles from health journalists, hospitals and universities. We link to them; we don't write or endorse them.

Cleveland Clinic · Sep 4, 2026

What you can do today: everyday supplements