Molecule
Vitamin D3
Cholecalciferol
A hormone the body makes from sunlight, that most people at northern latitudes are functionally deficient in, and that raises hard longevity endpoints.
Summary Can vitamin D supplements help me live longer and stay healthier? Show / hide ↓
Vitamin D3 is a hormone-like substance your body makes from sunlight, and it helps maintain bones, muscles, and immune function. Very low vitamin D levels, below 30 nmol/L, are linked to higher death rates and more serious infections, but this does not prove that supplements prevent these problems. Studies suggest modest protection against respiratory infections and about 17% lower cancer mortality in some groups, especially people who started with low levels. Benefits for heart disease, falls, and broken bones are less consistent and seem greatest in people who are deficient. A blood test can guide use; many people need about 1,000–4,000 IU daily, while long-term doses above 10,000 IU daily may be harmful.
What this means for you: Vitamin D3 is most worth considering if a blood test shows very low levels or you get little sunlight. It may offer some health benefits, but it is not proven to extend life for everyone.
moderate evidenceVitamin D3 is more accurately a hormone the body synthesizes from cholesterol when UVB light hits skin. It regulates calcium and bone metabolism, immune function, and dozens of downstream pathways.
Deficiency (serum 25(OH)D under 30 nmol/L or 12 ng/mL) is associated with higher all-cause mortality, higher cardiovascular disease, and more severe respiratory infections. This is strong, replicated observational evidence. The question is whether raising 25(OH)D through supplementation reverses these outcomes.
Trial evidence is partly positive. VITAL trial (2000 IU/day) reduced cancer mortality by ~17% in some subgroups. Meta-analyses of respiratory infection show modest reduction with daily dosing (large single-dose regimens do not work). Effects on cardiovascular events, fall prevention, and fracture reduction depend heavily on baseline status: benefits are largest in people who started deficient.
Practical: test blood 25(OH)D. Target range for optimal health is roughly 75-125 nmol/L (30-50 ng/mL). Most people need 1000-4000 IU/day of D3 to reach that range, less in summer if they get sun, more in winter and at higher latitudes. Very high doses (over 10,000 IU/day chronic) can risk hypercalcemia.
D3 is fat-soluble. Absorption is materially better when taken with the largest fatty meal of the day, roughly 30% higher than fasted intake. Take it with breakfast if breakfast is your biggest meal, or dinner otherwise.
K2 (MK-7) is often paired with D3. The rationale is that D3 increases calcium absorption and K2 directs calcium to bone rather than arteries. Human evidence for this pairing on hard endpoints is modest but plausible. It is a low-cost hedge.
Products with this: Vitamin D3
Further reading
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