Mechanism of Action
Multivitamins typically contain 15–30 vitamins and minerals at doses near the recommended daily values (NRV). They are designed to fill nutrient gaps from incomplete diets. Benefits depend heavily on individual nutritional status.
Evidence
Results from large RCTs are mixed. PHS II (n=14,641) showed a modest 8% cancer risk reduction but no cardiovascular effect. COSMOS (n=21,442) found unexpectedly positive effects on cognition in older adults. For overall mortality, meta-analyses show no effect. The bottom line: multivitamins don’t harm, but benefits in well-nourished individuals are marginal.
Who benefits most:
- Vegans/vegetarians (B12, iron, zinc)
- Older adults (D3, B12, calcium)
- Pregnant women (folate, iron, iodine)
- Those with restricted diets
Safety
Multivitamins are considered very safe at recommended doses. Risks from overdose: Vitamin A (liver toxicity), iron (in hemochromatosis), Vitamin E (bleeding risk). Drug interactions possible (Vitamin K + anticoagulants).
Dosage
1 capsule/tablet per day as directed. Don’t combine with single-nutrient supplements without checking upper limits (UL).