Vitamins
Vitamin evidence is strongest where it started: correcting a documented deficiency. A form like vitamin D3 in someone who tests low has solid trial backing behind the correction itself. That evidence gets thinner once you're already replete and supplementing for a general benefit on top of adequate levels — read the grade on each product rather than assuming vitamin status alone justifies a dose.
9 products · sorted by evidence grade
Common questions
Which vitamin supplements actually have the best evidence?
In this category the grade-A products are vitamin D3 (grade A for bone health and immune function), vitamin C (grade A — modestly shortens colds; a Cochrane review of 29 trials found about 8% shorter colds in adults, though it doesn't prevent them for most people), folate (grade A specifically for preventing neural tube defects when taken before and during early pregnancy), and B-complex (grade A only for correcting deficiency in at-risk groups like vegans, older adults, and pregnancy). Vitamin K2 (MK-7) sits a notch lower at grade B — a promising signal for arterial and bone health, but resting largely on a 3-year trial in postmenopausal women, with only a newer, smaller 2-year trial in coronary-artery-disease patients extending it; not yet replicated at scale. One honest caveat: several of these A grades are about correcting a common shortfall or preventing a specific problem — vitamin D3's benefits are strongest in people who start deficient, B-complex's A grade is purely deficiency correction, and folate prevents a defined birth defect — rather than boosting an already-healthy person. Vitamin C is the partial exception, since its modest cold-shortening effect shows up in the general population, not just the deficient.
Do I really need a vitamin supplement if I eat a decent diet?
For most healthy people eating varied food, the honest answer is usually no — B-complex, for instance, only earns its grade A in specific groups (vegans, older adults, pregnancy), and its energy claim is graded B because there's no trial showing extra energy in people who aren't deficient. The strongest general exception is vitamin D3 (grade A), since deficiency is genuinely common in people who work indoors or live at higher latitudes. Folate is a clear must (grade A) if you're pregnant or could become pregnant, but note its immune-support claim is only grade C. Don't expect vitamin C to keep you from getting sick — the evidence supports shorter colds, not fewer of them.
When the evidence changes, we’ll tell you.
One short email a month. New A-grades, downgraded claims, and reader questions.
Medical disclaimer. The information on this site is provided for educational purposes only and is not intended as medical advice. It does not constitute a diagnosis, treatment plan, or recommendation for any specific health condition. Always consult a qualified healthcare professional before making changes to your supplement regimen, diet, or lifestyle — especially if you are pregnant, nursing, taking medications, or managing a medical condition.
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