Supplements with Strong Evidence
| Supplement | Who Benefits | Evidence |
|---|---|---|
| Vitamin D | Nearly everyone in northern latitudes, especially in winter | Strong — corrects deficiency, bone health |
| Folic acid | All women trying to conceive/pregnant (first trimester) | Very strong — prevents neural tube defects |
| Vitamin B12 | Vegans, vegetarians, those with pernicious anaemia/absorption issues | Strong — corrects deficiency |
| Iron | Those with confirmed iron deficiency | Strong — corrects deficiency anaemia |
| Omega-3 (fish oil) | Those not eating oily fish 2×/week | Moderate — cardiovascular and triglyceride benefits |
| Calcium + Vitamin D | Osteoporosis risk, on long-term steroids | Strong for bone health in deficient individuals |
Supplements with Weak or No Evidence
| Supplement | Claim | Evidence Quality |
|---|---|---|
| Detox teas/juices | 'Cleanse' the body | No evidence — kidneys and liver already do this naturally |
| Collagen supplements | Skin/joint health | Weak, inconsistent evidence |
| Immune-boosting blends | Prevent illness | Little to no evidence for most products |
| High-dose vitamin C | Prevent/cure colds | May modestly reduce duration; doesn't prevent colds |
| Glucosamine/chondroitin | Joint pain relief | Mixed evidence — modest benefit at best for some people |
Test Before You Supplement
Where possible, get relevant blood levels checked (vitamin D, B12, ferritin) before starting supplements — this avoids unnecessary spending, prevents overdosing on fat-soluble vitamins (A, D, E, K which can accumulate to toxic levels), and ensures you're treating an actual deficiency.Supplements Aren't Regulated Like MedicationsIn most countries, supplements face far less rigorous testing and regulation than medications — manufacturers don't need to prove effectiveness before selling. Be sceptical of dramatic health claims, especially those promising to 'boost immunity' or 'detox' the body.
Do multivitamins prevent disease in healthy, well-nourished people?
Large studies (including the Physicians' Health Study II) have found little to no benefit from multivitamins in preventing cancer or cardiovascular disease in generally well-nourished adults.
Is it possible to take too much of a vitamin?
Yes, especially fat-soluble vitamins (A, D, E, K) which accumulate in the body. Vitamin A excess can cause liver damage and birth defects; vitamin D excess can cause dangerous hypercalcaemia. Water-soluble vitamins (B, C) are generally excreted in excess, though very high doses of B6 can cause nerve damage.
Should I tell my doctor about supplements I take?
Yes, always — some supplements interact significantly with medications (e.g. St John's Wort reduces effectiveness of many drugs including contraceptives and antidepressants; vitamin K affects warfarin).
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.