The global supplement industry is worth over $150 billion a year. Most of that money is spent by people who do not need supplements and will gain no meaningful benefit from them. A smaller group of people genuinely need specific supplements and are not getting them. Here is the honest guide to who actually needs what, what the evidence actually says, and what is pure marketing.

What is a Nutrient Supplement?

A nutrient supplement is any product taken by mouth that contains a vitamin, mineral, herb, amino acid, or other substance intended to supplement the diet. They come as tablets, capsules, powders, liquids, and gummies.

The critical distinction: supplements are not medicines. In most countries, they do not require the same level of testing, evidence, or regulatory approval as pharmaceutical drugs. A drug must prove it is effective before it can be sold. A supplement must only prove it is not acutely harmful.

This means manufacturers can make very broad claims — "supports immunity," "promotes energy," "aids brain health" — without rigorous evidence that their product actually does any of these things in a healthy person with an adequate diet.

If you have a genuine nutritional deficiency, the right supplement can be transformative. If you do not have a deficiency, taking that same supplement will likely do nothing useful — and could occasionally cause harm.

Supplements With Strong Evidence — Who Genuinely Needs Them

Folic Acid — Women Planning Pregnancy or in Early Pregnancy

This is the clearest, most evidence-backed supplementation recommendation in all of medicine. Folic acid (vitamin B9) taken before conception and through the first 12 weeks of pregnancy reduces the risk of neural tube defects — serious birth defects of the brain and spine (spina bifida, anencephaly) — by up to 70%.

The neural tube closes in the first 28 days of pregnancy — often before a woman even knows she is pregnant. This is why folic acid supplementation must start before trying to conceive, not after a positive test.

Recommended dose: 400 micrograms daily before conception and through the first trimester. Women with a previous neural tube defect pregnancy need 4mg (10 times higher) — prescribed by a doctor.

This supplement saves lives and prevents disability. Every woman who could become pregnant should know this.

Vitamin D — Widely Deficient Despite Living in a Sunny Country

Vitamin D is synthesised in the skin when exposed to UVB sunlight. You would think people living in Ghana — close to the equator, with intense sunlight year-round — would have no risk of deficiency. The reality is surprisingly different.

Many people in urban Ghana spend the majority of their day indoors — in offices, schools, homes, and vehicles. Those who do go outside often do so when the sun angle is too low for effective UVB synthesis (early morning and late afternoon). Darker skin also requires more sun exposure to synthesise the same amount of vitamin D as lighter skin.

Vitamin D deficiency is common and causes: weak bones (rickets in children, osteoporosis and fracture risk in adults), impaired immune function, muscle weakness, and fatigue. Severe deficiency is linked to increased risk of respiratory infections, depression, and certain cancers.

Who should consider supplementing: People who spend most time indoors, older adults (skin efficiency declines with age), people with darker skin living in lower-sunlight environments, breastfed infants (breast milk is low in vitamin D), and anyone with confirmed deficiency on a blood test.

Recommended dose: 400–2,000 IU daily for adults; more if deficient (follow doctor's guidance). Blood test (25-OH vitamin D) confirms status.

Iron — Specific Groups at Real Risk

Iron deficiency anaemia is the most common nutritional deficiency worldwide, and it is genuinely debilitating — causing exhaustion, weakness, impaired concentration, and reduced immunity. But iron supplementation should not be taken randomly — excess iron is toxic and can cause organ damage.

Who genuinely needs iron supplementation:

  • Women with heavy menstrual periods — losing significant iron monthly
  • Pregnant women — blood volume expands by 50% in pregnancy; iron demands increase dramatically
  • People with confirmed iron deficiency anaemia on a blood test
  • Frequent blood donors
  • Infants and young children in areas where dietary iron is inadequate
  • People with certain gut conditions that impair iron absorption (coeliac disease, inflammatory bowel disease)

Important: A full blood count and serum ferritin test should confirm deficiency before supplementing. Do not take iron supplements without a confirmed deficiency.

Vitamin B12 — People Who Avoid Animal Products

Vitamin B12 is found almost exclusively in animal products — meat, fish, eggs, and dairy. It is essential for red blood cell formation, nerve function, and DNA synthesis. Deficiency causes megaloblastic anaemia (large, dysfunctional red blood cells) and peripheral neuropathy (nerve damage causing tingling and weakness).

People who eat animal products regularly are very unlikely to be deficient. Those at risk include strict vegetarians and vegans, older adults (stomach acid production decreases with age, reducing B12 absorption), and people taking metformin long-term (reduces B12 absorption).

Recommended dose for vegans/vegetarians: 250 micrograms daily, or a higher weekly dose. Confirmed by serum B12 blood test.

Iodine — Where Deficiency is Endemic

Iodine is essential for thyroid hormone production, which regulates metabolism, growth, and brain development. Deficiency during pregnancy causes intellectual disability in the child. In areas where soil is iodine-poor, dietary iodine is low.

The simplest solution — and one of the most cost-effective public health interventions in history — is iodised salt. Using iodised salt in cooking eliminates iodine deficiency for virtually the entire population at minimal cost. Ghana's Food and Drugs Authority mandates iodisation of salt sold in Ghana.

Pregnant women who eat very restricted diets may still need a supplement containing iodine.

Omega-3 Fatty Acids — Those Who Eat Little or No Fish

Omega-3 fatty acids — particularly EPA and DHA — are essential for brain function, heart health, and reducing chronic inflammation. The best dietary sources are oily fish (sardines, mackerel, herring, salmon). People who eat oily fish two or more times per week likely get adequate omega-3.

Those who eat little or no fish, or who are vegetarian or vegan (plant omega-3 sources are less efficiently converted), may benefit from supplementation. Fish oil capsules or algae-based omega-3 (the source fish themselves use) are both effective.

For people who have already had a heart attack, high-dose omega-3 supplements have demonstrated benefit in reducing cardiovascular events.

Supplements That Are Mostly Hype

Multivitamins for Healthy People With Adequate Diets

The largest and most rigorous studies on multivitamin use in healthy adults have consistently found no benefit for overall mortality, cancer rates, or cardiovascular disease. The 2012 Physicians' Health Study II — 14,000 doctors followed for over a decade — found no benefit from daily multivitamins on any major health outcome.

If your diet is varied and adequate, your body already has what it needs. A multivitamin adds nothing meaningful and the fat-soluble vitamins (A, D, E, K) can accumulate to harmful levels with persistent excess.

"Immune Boosting" Supplements

The immune system cannot simply be "boosted" by a supplement — it is not a muscle that grows stronger with training. It is a complex, finely balanced system. Vitamin C supplementation has been extensively studied and found to reduce duration of colds by about half a day in people who are already deficient — no effect in those with adequate dietary intake.

Zinc supplementation may slightly reduce cold duration if taken within 24 hours of symptom onset — but the evidence is inconsistent and high doses cause nausea.

Collagen Supplements for Skin

Collagen is a protein. When you eat it — in any form — your digestive system breaks it down into amino acids, exactly like any other protein. It does not travel to your skin intact. The amino acids are distributed throughout the body based on need. There is no evidence that collagen supplements preferentially improve skin collagen levels compared to eating adequate protein from any other source.

Fat-Burning and Testosterone-Boosting Supplements

The market for these is enormous and the evidence is almost universally poor. Most "fat burners" either do nothing or cause harm through stimulant ingredients. Most "testosterone boosters" contain herbs with no demonstrated effect on testosterone in clinical trials. Some have been found to contain unlabelled pharmaceutical ingredients. Avoid.

When More is Dangerous

Fat-soluble vitamins — A, D, E, and K — are stored in body fat and the liver and can accumulate to toxic levels:

  • Vitamin A toxicity — causes liver damage, bone loss, birth defects in pregnancy. Pregnant women should avoid high-dose vitamin A supplements and limit liver consumption.
  • Vitamin D toxicity — causes hypercalcaemia (too much calcium in blood), kidney stones, and kidney damage. Possible with very high supplemental doses taken long-term — not from sun exposure.
  • Iron toxicity — excess iron generates free radicals, damages organs. Particularly dangerous in children — iron supplement overdose is a leading cause of fatal childhood poisoning.
  • Vitamin E in high doses — large trials have shown increased mortality with high-dose supplementation; now generally discouraged

Before Taking Any Supplement — Ask These Questions

  • Has a blood test confirmed I am deficient in this nutrient?
  • Am I in a group known to be at risk of this deficiency (pregnant, elderly, vegan, indoor worker)?
  • Is there good clinical evidence this supplement benefits people in my situation?
  • Could I get this nutrient from food instead?
  • Does my doctor or pharmacist know I am taking this?
  • Does this supplement interact with any medication I take?

If you cannot answer yes to the first or second question, you almost certainly do not need the supplement.

The supplement industry profits enormously from the idea that everyone is deficient and everyone needs extra nutrients. The evidence does not support this. For most healthy people eating a reasonably varied diet, supplements offer no benefit. The money spent on unnecessary supplements would achieve far more invested in better food. But for specific groups — pregnant women, the elderly, vegans, people with confirmed deficiencies — the right supplement at the right dose genuinely changes lives. The key word is specific. Targeted supplementation based on actual need is smart medicine. Broad supplementation based on marketing is expensive urine.