Multivitamin

What it is

A multivitamin combines a range of vitamins, and often minerals, in one tablet or capsule. Formulas vary enormously, from basic once-a-day products to sports and age-specific blends with dozens of ingredients.

People take them to fill dietary gaps, for general health and for peace of mind. They make most sense for people with restricted diets, poor appetite, older age, or specific needs in pregnancy.

For well-fed adults, large studies have found little or no effect on heart disease, cancer or death rates, though results vary slightly by trial and population.

How it works

They provide small amounts of many nutrients, so you are less likely to fall short on any one. They do not undo a poor diet, which also supplies fibre, protein and other compounds supplements lack.

What the evidence says

• Moderate Covering gaps in restricted or poor diets
  Useful where intake is genuinely low, such as vegans, older adults or people with absorption problems.
• Strong Preventing specific deficiencies
  Works where deficiency exists, though targeted supplements may be better.
• Weak Reducing major disease like cancer or heart disease
  Large trials in well-nourished adults show little or no effect.
• Limited Eye health or cognition in older adults
  Some trials show small benefits in certain groups, including cognition in older adults; results are modest and not consistent.
• Limited Energy and wellbeing
  Small mood and energy improvements are reported in some trials, probably in those with marginal intake.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Follow the label; one a day is typical. More is not better.
• Take with food to improve absorption and reduce nausea.
• Check the total of vitamin A, vitamin D and minerals if you also take other supplements, cod liver oil or fortified products.
• Pregnant women should use a pregnancy-specific product with folic acid and no retinol, and follow NHS advice.

Forms and what to look for

• Standard tablets and capsules are cheap and reliable.
• Gummies are tasty but often contain sugar and may lack minerals like iron.
• Gender-, age- and pregnancy-specific formulas tailor doses; look for ones aligned with UK reference intakes (NRVs).
• Chelated minerals and "whole-food" blends are marketed as better; evidence of real advantage is limited.
• Look for formulas close to 100 percent of NRV rather than thousands of percent.

What to expect, and when

• If your diet is poor, deficiency symptoms may improve over weeks to months.
• Most people notice no change.
• Do not expect protection from long-term disease; evidence for this is lacking.

Side effects

• Nausea or stomach upset, especially on an empty stomach.
• Constipation or dark stools if the product includes iron.
• Metallic taste.
• Bright yellow urine from riboflavin, which is harmless.

Interactions

• Warfarin: vitamin K content can alter its effect.
• Levothyroxine, some antibiotics (tetracyclines, quinolones) and bisphosphonates: minerals like calcium, iron and zinc can reduce absorption, so separate doses by several hours.
• Methotrexate: folic acid content matters.
• Other supplements: stacking can push intakes of vitamin A, zinc, iron or B6 too high.

Who should avoid it

• Men and post-menopausal women should usually avoid products containing iron unless advised.
• Pregnant women should avoid products with retinol (vitamin A) and use pregnancy-specific formulas.
• Smokers should avoid beta-carotene-heavy formulas.
• People with kidney disease, haemochromatosis or on complex medications should check with a clinician.

Risks and safety

• Taking multiple products can cause unnoticed overdose of fat-soluble vitamins or minerals.
• Iron is a leading cause of poisoning in children; keep out of reach.
• Sports multivitamins can occasionally be contaminated; choose batch-tested products if you compete.
• Not banned in sport in themselves, but ingredient blends sometimes include unlisted substances.

Buying well: quality and testing

• Look for NSF, USP, Informed Sport or similar third-party testing.
• Prefer products that list doses of each nutrient as a percentage of NRV.
• Avoid proprietary blends that hide amounts.
• Be sceptical of megadose claims; more of everything is not better.

Bottom line

A basic multivitamin is a low-cost safety net for people with limited diets, but it will not make a poor diet healthy and is unlikely to improve long-term health in people already eating well. Choose a simple, moderate-dose product and avoid doubling up with other supplements.