Vitamin D in older adults
EFSA's adequate intake is 15 micrograms a day. Ageing skin synthesises less, indoor living supplies less sun, and the shortfall is common.
goodWell supported, with the usual caveats about effect size.Revised 10 Jul 2026
Above roughly 40° north there is no useful UVB between October and March.Photograph: Jair Lázaro / Unsplash
Definition
A fat-soluble vitamin obtained from sunlight on skin, from a short list of foods, and from supplements. Its established role is in calcium and phosphate handling, and therefore in bone.
The number
EFSA sets an adequate intake of 15 micrograms (600 IU) per day for adults, under the explicit assumption of minimal cutaneous synthesis — that is, for the case where sunlight is contributing nothing.
Why older adults are a special case
Three things stack:
- Skin synthesises less. The concentration of the precursor in skin falls with age, so the same sun exposure produces less vitamin D.
- Exposure falls. Less time outdoors, more clothing, and in care settings sometimes none at all.
- Intake is often low. Appetite and dietary variety decline, and the rich food sources — oily fish especially — are not universally eaten.
Add a northern latitude, where there is no useful UVB between roughly October and March, and deficiency stops being unusual.
What supplementation is good for
Correcting deficiency. Where status is genuinely low, supplementation improves bone outcomes and is part of standard fracture prevention alongside calcium. This is the well-supported use.
Everything else — the long list of claimed effects on cancer, cardiovascular disease, respiratory infection, mood and mortality — has performed poorly in large randomised trials of supplementation in already-replete populations. The pattern across the literature is consistent: low vitamin D is associated with poor health, and giving vitamin D to people who are not deficient generally does not improve it. Low status appears to be partly a marker of ill health rather than a cause of it.
Correcting a deficiency is worth doing. Topping up an adequacy is not the same intervention, and it has repeatedly failed to work.
Dosing and a caution
Modest daily supplementation — in the region of the adequate intake — is the form that has behaved best. Very large intermittent doses have produced worrying results, including increased falls in some trials, which is the opposite of the intended effect.
Vitamin D is stored, and excess is possible. EFSA has set tolerable upper intake levels; high-dose products sold online sit far above the reference intake.
How to know
A 25-hydroxyvitamin D blood test, interpreted by a doctor who knows the rest of your history. It is the one supplement question where testing is cheap, available and genuinely informative.