Nutrition · · 6 min read

Vitamins and supplements: who needs them, who does not

A supplement makes sense when there is a specific reason for it, such as a deficiency, pregnancy or a diet that leaves a gap. For healthy adults, most studies show little or no effect of a daily multivitamin on the risk of health problems, and it cannot take the place of a varied diet. Natural does not mean safe: supplements can interact with medicines, and some are harmful in excess.

Illustration of three supplement bottles with red, dark and teal caps and a few loose capsules beside them

In short

  • A supplement helps most when there is a clear reason, such as a deficiency, a medical condition or pregnancy.
  • Most studies show little or no effect of multivitamins on the risk of health problems in healthy adults.
  • Natural does not mean safe. Supplements can interact with medicines and some cause serious harm.
  • Total intake from food, fortified foods and supplements together should stay within safe upper limits.
  • Tell every provider about everything you take, and do so well before surgery.

When a supplement makes sense

  1. Folic acidThe CDC says anyone who could become pregnant should get folic acid daily, starting at least a month before trying to conceive, because neural tube defects can occur before many people know they are pregnant.
  2. Vitamin B12B12 is not found naturally in fruit, vegetables and grains, so vegans may fall short.
  3. Vitamin DThe NHS advises people who are rarely outdoors, who cover most of their skin outside, or who have darker skin to consider a supplement all year, and babies and young children have their own guidance.
  4. Other nutrientsCalcium, iron and others can be needed when a deficiency is confirmed or when a condition limits absorption. Iron in particular should be taken only when a provider recommends it.

In each case the reason comes first, and a provider can tell you what form is right for you and for how long.

Where research finds little benefit

The effect of multivitamin and multimineral products on disease risk is hard to study, partly because people with healthier lifestyles are more likely to take them. Even so, most studies have shown little or no effect on the risk of health problems, and these products cannot take the place of eating a variety of foods.

A basic daily multivitamin is unlikely to pose a health risk for healthy people. That does not make it a strategy. Money and attention may go further on vegetables, fruit, whole grains, beans, fish and sleep.

Risks: excess and interactions

  • Vitamin A in excess during pregnancy has been linked to birth defects. Smokers should avoid products with large amounts of vitamin A, which have been linked to higher lung cancer risk.
  • Too much vitamin D over a long time can cause calcium to build up, which can weaken bones and damage the kidneys and heart.
  • Very high amounts of vitamin B6 can cause nerve damage in the arms and legs.
  • St. John's wort makes many medicines less effective.
  • Vitamin K matters if you take warfarin, so talk to your provider first.
  • Some supplements increase bleeding risk or affect anesthesia.
  • Kava has been linked to liver disease.

Duplication is a quiet problem. A multivitamin, a separate vitamin D, an omega-3 and a product for hair may share an ingredient, and the total can pass the safe limit without your noticing. Before buying a new product, write down what you already take.

How to read a label

  1. Look at the active ingredientCheck the specific compound and the amount per serving, not the brand name.
  2. Check the serving sizeThe amount shown may be for two or three capsules.
  3. Watch the daily valueHigher is not always better. Many nutrients have an upper limit.
  4. Do not assume the label is accurateWhat is on the label may not match what is in the bottle, and a term like standardized does not guarantee quality.
  5. Treat disease claims as a warningLabels cannot claim to diagnose, treat or prevent disease. Weight loss, sexual enhancement and bodybuilding products may contain undeclared prescription drugs.

The FDA does not describe approving supplements before sale. Companies are responsible for the safety and labeling of their products, and the FDA can act after a product reaches the market.

Pregnancy, children and long-term conditions

Many supplements have not been tested in pregnant or breastfeeding women or in children. Prenatal vitamins and folic acid have a clear role in pregnancy, but other products should be cleared with your obstetric provider first.

Iron supplements are a leading cause of poisoning in young children, so keep all supplements out of reach. If you have kidney or liver disease, take blood thinners or have surgery planned, check your whole list with your provider.

How to decide

  1. Name the goalWhat exactly do you want to change, and how will you know it worked?
  2. Look for a reasonA confirmed deficiency, a medical condition or pregnancy is a reason. A hunch is not.
  3. List everything you takeInclude medicines and check for duplication and interactions.
  4. Ask your provider or pharmacistDiscuss the form, duration and how you will monitor it.
  5. Set a review dateAfter a few months, decide whether to continue.

Red flags

If you have side effects, stop the supplement and contact your provider. Call 911 or go to an emergency department for trouble breathing, swelling of the face or throat, fainting or confusion. Get prompt medical advice for yellowing skin or eyes, dark urine, pain in the upper right abdomen, a new rash, unusual bruising or bleeding, or persistent vomiting.

Be wary of the product itself when it promises to fix a disease, has a secret formula, lacks a full ingredient list, or comes from a seller with no documentation.

Questions for your provider or pharmacist

  • Is there a reason I should take this supplement?
  • Do I need a blood test first?
  • Does it interact with my medicines?
  • How long should I take it?
  • Should I stop it before surgery, and when?

Questions and answers

Should a healthy person take a multivitamin?

Usually there is no strong reason. A basic multivitamin is unlikely to cause harm in healthy people, but studies show little to no effect on health problems and food remains the priority.

Can supplements be harmful?

Yes. Excess vitamin A and vitamin D, some herbal products and interactions with medicines can all cause problems, even when the product is labeled natural.

How can I judge quality?

A full ingredient list, a serving size you understand and no claims to treat disease are good signs. Be wary of labels that look too good to be true, since contents can differ from the label.

Can I take several supplements together?

Only after checking for the same ingredient appearing twice and for interactions. Combinations are a common way to exceed safe limits without noticing.

Do I stop supplements before an operation?

Tell your surgical team about every product well ahead, because some raise bleeding risk or affect anesthesia. They will say which to pause and when.

Sources

  1. NCCIH — Using dietary supplements wisely
  2. NCCIH — Vitamins and minerals
  3. FDA — Dietary supplements
  4. CDC — About folic acid
  5. NHS — Vitamin D
  6. NHS — Vitamin B

Sources checked on 29 October 2026.

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