Autumn arrives and vitamin D is back in the conversation. That’s no accident: it’s a vitamin unlike the others, because its main source isn’t on your plate — it’s in the sun.

Where does vitamin D come from?

Most vitamin D is produced in the skin when it’s exposed to ultraviolet B radiation. In the winter months, with shorter days, a lower sun and more time spent indoors, that production tends to drop — even in a country as sunny as Portugal.

Clothing, sunscreen, age and skin tone also affect how much we can produce. That’s why there’s no single rule that fits everyone.

Lifestyle counts too. If you work in an office, get around by car and spend the weekend indoors, you may get very little direct sun, even on lovely days. On the other hand, sun exposure calls for common sense: never skip the sunscreen in the hottest hours just for the sake of vitamin D.

What about food?

Few foods are naturally rich in vitamin D, but some are old friends of Portuguese cooking:

  • Oily fish such as sardines, mackerel, salmon and horse mackerel.

  • Egg yolk.

  • Fortified foods, such as some plant-based drinks, cereals or yoghurts — check the label.

  • Mushrooms exposed to UV light, in more modest amounts.

A simple idea for winter: tinned sardines or mackerel on bread once or twice a week, and eggs at breakfast or dinner. It won’t solve everything, but it helps vary your sources.

In winter, the sunshine vitamin asks for a little more attention.

What does it do?

Vitamin D has several recognised functions in the body:

Vitamin D contributes to the maintenance of normal bones and teeth.

Vitamin D contributes to the maintenance of normal muscle function.

Vitamin D contributes to the normal function of the immune system.

More isn’t better

Because it’s a fat-soluble vitamin, vitamin D builds up in the body. Always stick to the recommended daily dose on the label and add up all your sources: if you already take a multivitamin, check how much it contains before adding another supplement.

If you’re unsure about your levels, only a blood test can tell you — talk to your doctor or pharmacist.

How to fit it into your routine

As it’s fat-soluble, it makes sense to take vitamin D with a meal that contains some fat, such as breakfast with eggs or a lunch dressed with olive oil. Choose a fixed moment and stick with it through the darkest months of the year.

In short

  • Your skin makes vitamin D with sunlight; in winter, that production tends to drop.

  • Oily fish, eggs and fortified foods help on the food side.

  • Stick to the dose on the label and add up all your sources.

  • Only a blood test can tell you what your levels are.

This article is for information only and is not a substitute for advice from a health professional.