Vitamin D and the prostate: why deficiency is so common

Vitamin D is unusual among nutrients: the body makes most of it rather than eating it, and the making depends on something as variable as how much sun reaches your skin. That is why deficiency is so common, even in sunny countries — and why a lot of men have never had it measured.

What it actually is

Despite the name, vitamin D behaves less like a vitamin and more like a hormone. Receptors for it are found throughout the body, including in prostate tissue, which is why it turns up in research well beyond bone health.

Its established role is in calcium absorption, bone maintenance, muscle function and normal immune function. That much is not in dispute and appears on the authorised list of health claims in the European Union.

Why so many people are short of it

• Latitude and season. Above roughly 37 degrees north — which includes most of Europe — the winter sun sits too low for the skin to make meaningful amounts of vitamin D at all, whatever the weather looks like.
• Indoor life. Sunlight through a window does not do it. The UVB wavelengths involved are blocked by glass.
• Sunscreen. It works as intended, and part of what it blocks is vitamin D synthesis. This is not an argument against sun protection; it is a reason not to rely on the sun alone.
• Age. Older skin produces less vitamin D from the same exposure. A man of 70 makes a fraction of what he made at 20.
• Skin tone. More melanin means more sun is needed for the same result — a real issue for darker-skinned people living far from the equator.

How it is measured

The blood test to ask for is 25-hydroxyvitamin D, written 25(OH)D. It is the storage form, and it reflects your status over the preceding weeks rather than what you did yesterday.

Results come in ng/mL or nmol/L, which causes endless confusion — 1 ng/mL is 2.5 nmol/L. Reference ranges vary between laboratories and expert bodies disagree at the margins, so the number is best interpreted by the doctor who ordered it rather than against something you found online.

Where it comes from

Sun. Short, regular exposure of a decent area of skin, outside the hours when burning is likely. Burning gives you no extra vitamin D and plenty of extra risk.

Food. The list is short. Oily fish — sardines, mackerel, salmon, herring — is the main dietary source worth the name. Egg yolks and some fortified foods contribute modestly. Realistically, diet alone rarely closes a real deficit.

Supplements. Where sun and diet do not suffice, this is the practical route, and it is exactly the situation where testing first makes sense. Vitamin D is fat-soluble and accumulates, so more is not automatically better; very high intakes taken indefinitely are not harmless.

The sensible position

The honest summary of the wider research is that vitamin D deficiency is common, that correcting a genuine deficiency is worth doing, and that the evidence for high-dose supplementation preventing specific diseases in people who are not deficient is considerably weaker than the enthusiasm around it suggests.

For a man over forty, the useful step is not to guess. Ask for the 25(OH)D test at your next appointment, find out where you actually stand, and decide from there with your doctor.

This article is general health information. It is not medical advice, and any decision about supplementation should be made with your doctor, ideally after a blood test.