Dietary supplements have become an increasingly familiar part of everyday health — from multivitamins and iron tablets to vitamin D, “immunity” powders and herbal products. But who actually needs them, and when can taking too much do more harm than good?

A 2019 analysis by Johns Hopkins researchers of 277 clinical trials found that most vitamin, mineral and other nutrient supplements were not associated with longer life or protection from heart disease. The findings also highlighted that some interventions may offer benefits in specific circumstances, while calcium combined with vitamin D was associated with a slightly increased stroke risk.

Yet supplements cannot be viewed through a one-size-fits-all lens, particularly in India, where nutritional deficiencies remain a concern. We spoke to Dr Amitav Banerjee, Epidemiologist and Public Health Expert, Professor Emeritus at D Y Patil Medical College, about who needs supplements, who doesn't, how to recognise deficiencies and the risks of overuse. Dr Banerjee is Professor Emeritus at Dr D Y Patil Medical College.

Excerpts from an interview

Q: Who genuinely needs dietary supplements, and who generally does not?

Dr Amitav Banerjee: People with a confirmed nutritional deficiency, those with restricted diets that exclude particular nutrients, people with malabsorption, certain chronic illnesses or increased nutritional requirements may genuinely need supplements. Pregnant women and infants are also important groups where specific supplements have established roles.

A healthy adult eating a reasonably varied diet generally does not need a multivitamin simply because they are tired, stressed or worried about immunity. The same applies to most healthy children eating a balanced diet. Just because a nutrient is essential doesn't mean everyone needs it in pill form.

Q: Which children may actually need supplements?

A: Infants are an important group. Many guidelines routinely recommend vitamin D for infants, particularly breastfed babies, because breast milk alone generally does not provide enough.

Children with very restricted diets, severe food allergies, feeding difficulties, eating disorders or poorly planned vegan diets may also need specific nutrients. Children with conditions such as coeliac disease, inflammatory bowel disease, cystic fibrosis, gastrointestinal surgery or other problems affecting absorption may require supplementation.

The key is to identify the nutritional gap and treat it, rather than giving a random multivitamin.

Q: What are the signs of a nutritional deficiency?

A: There is no single universal sign. Iron deficiency can cause anaemia, fatigue, weakness and poor concentration. B12 deficiency can cause anaemia, a sore tongue, numbness, tingling, and neurological problems. Folate deficiency can also cause anaemia, while vitamin D deficiency may cause bone pain and muscle weakness.

But symptoms alone are rarely enough to diagnose a deficiency.

Q: Does fatigue, hair loss, poor concentration or frequent illness mean someone needs supplements?

A: Not necessarily. These are clues, not diagnoses.

Fatigue, for example, can result from poor sleep, anaemia, thyroid problems, infection, stress, or many other conditions. Hair loss can have nutritional, hormonal, genetic or dermatological causes.

The approach should be to find the underlying cause rather than assuming that a supplement will solve the problem.

Q: Does everyone need a blood test before taking a supplement?

A: No. It depends on the nutrient and the individual situation.

Testing can be useful for deficiencies such as iron, B12, folate, and vitamin D, but you also need to interpret results in context. On the other hand, some preventive supplements are recommended without testing.

Folic acid around conception is a good example. You don’t wait for a deficiency test because neural-tube development occurs very early in pregnancy. Similarly, many guidelines routinely recommend vitamin D for breastfed infants without first doing a blood test.

Q: How much of the marketing around “immunity”, brain health, growth and sleep is actually backed by evidence?

A: It varies considerably. There is an important difference between saying that a nutrient is needed for normal immune function and claiming that a supplement will prevent infections.

For healthy children, there is no good evidence that supplements generally “boost immunity” or prevent serious illness. The strongest evidence is usually for correcting a deficiency or meeting a specific nutritional requirement.

Parents should therefore ask what the product has actually been shown to do, at what dose and in whom.

Q: How should people interpret claims such as “clinically proven”, “supports immunity” or “detox”?

A: Don’t take these claims at face value. Ask: clinically proven to do what, in whom, at what dose, and compared with what?

“Supports immunity” does not necessarily mean fewer infections. “Detox” is often a marketing term rather than a clearly defined medical outcome. And a testimonial or a doctor’s endorsement is not the same as evidence from an independent clinical guideline or good-quality trial.

Q: Can taking too many supplements or high doses cause harm?

A: Absolutely. More is not better.

For nutrients, there is often a range from deficiency to adequacy and then excess and toxicity. High doses of vitamin A can be toxic and are particularly concerning during pregnancy. Excess vitamin D can raise calcium levels and cause kidney problems. Too much iron can be dangerous, especially in children. High doses of vitamin B6 can cause nerve damage, while excess zinc can cause copper deficiency.

A vitamin or mineral is not automatically safe simply because it is a nutrient.

Q: Can supplements compensate for a poor diet?

A: Not completely. Supplements can provide specific nutrients, but they cannot reproduce everything food provides — including protein, fibre, essential fats and a range of naturally occurring compounds.

At the same time, food cannot always provide enough of a particular nutrient, which is where targeted supplementation becomes important.

The simplest approach is: food first where practical, targeted supplements where necessary.

Q: What is the biggest mistake parents make with supplements?

A: Giving several products without checking whether their ingredients overlap.

A child may receive a multivitamin, vitamin D, fortified foods, an “immunity” powder, and gummies, all containing some of the same nutrients. Individually, they may appear harmless, but together the dose can become excessive.

Every supplement should have a specific reason. And remember that gummies are supplements, not sweets.

Q. When does supplementation make sense?

There are several situations:

  • A confirmed deficiency, such as iron-deficiency anaemia.
  • A predictable nutritional gap, such as vitamin D for many breastfed infants.
  • Increased requirements during particular life stages, such as folic acid around conception and pregnancy.
  • Diets that naturally lack certain nutrients, such as B12 in a strict vegan diet without adequate fortified foods.
  • Medical conditions that affect nutrient absorption.

The simplest way to think about it is: eat food first where practical, and use targeted supplements where necessary.

Q: What are the key nutrients at different life stages?

Some nutrients have particularly well-established roles.

Pregnancy/preconception: folic acid; many guidelines recommend iron and folic acid supplementation.

Infancy: many guidelines routinely recommend vitamin D.

Strict vegan diet: vitamin B12 usually comes from supplements or reliably fortified foods.

Confirmed deficiency: targeted treatment, such as iron for iron deficiency.

Malabsorption or gastrointestinal disease: supplementation depends on the condition and laboratory findings.