Vitamin D deficiency is common in Belgium: an estimated 67% of the population has an insufficient intake. The explanation is mainly geographical. Between October and March the sun sits too low for your skin to produce vitamin D, and food only supplies a small part of what you need. The reserves you build up in summer are therefore gradually used up over the winter. Here is why this shortfall is so widespread, what vitamin D actually does in your body, and how to top up your intake during the dark months.
Why vitamin D runs short in winter
Your skin produces vitamin D under the influence of UVB rays. At our latitude, around the 50th parallel, those rays only reach the ground with enough intensity between spring and early autumn. From October to March the sun is too low: even a long walk on a clear day no longer produces any vitamin D.
Our way of living adds to this. We spend most of the day indoors, often behind a window, and glass blocks UVB. In summer, sunscreen, which your skin genuinely needs, also reduces production. Food does not really make up the difference: oily fish, egg yolk and a few fortified products are the only notable sources, and even then in modest amounts.
What vitamin D does in your body
Its functions are well documented and officially recognised at European level. Vitamin D contributes to the maintenance of normal bones and normal teeth. It contributes to the normal function of the immune system. It supports normal muscle function, promotes the normal absorption and use of calcium and phosphorus, and plays a role in the process of cell division.
Its role therefore sits mainly with the skeleton, the muscles and immunity. That also explains why interest in vitamin D grows as winter approaches, the season when the immune system is under the most pressure.
Who is most at risk of a vitamin D deficiency
Some situations reduce natural production or increase requirements:
- people who rarely go outside or work indoors all day;
- older people, whose skin produces vitamin D less efficiently;
- darker skin, which needs longer exposure to produce the same amount;
- people who cover most of their skin when they go out;
- people who are overweight, since vitamin D is stored in fat tissue.
If you are pregnant, breastfeeding or taking medication, ask your doctor or pharmacist for advice before starting a course.
How to know whether you are getting enough
The signs of a low intake are not specific and can have many other causes. Vitamin D shares that with other nutrients: the signs of magnesium deficiency are just as hard to read. The only reliable way to know where you stand is a blood test measuring your 25-hydroxyvitamin D level, requested by your doctor, who will also interpret the result in your own context.
One useful point while we are here: tiredness is often attributed to vitamin D a little too quickly. It is mainly the B vitamins and vitamin C that carry a recognised claim on that, as we explain in our article on B vitamins and energy.
Which dose to choose: 1000 or 2000 IU
For daily maintenance through the winter, one capsule of Vitamin D3 1000 in an olive oil base is enough for most adults, with the option of going up to two capsules. If you rarely get outside, or your doctor has found a deficiency, a higher dose may suit you better: Vitamin D3 2000 in softgels provides 50 µg per serving, with one capsule a day.
Vitamin D3, or cholecalciferol, is the form your skin makes itself. Because it is fat-soluble, it is best to take your capsule with a meal containing some fat, which helps absorption. On our labels the intake is expressed as a percentage of the reference intakes.
D3 on its own or D3 with K2
This question comes up often. Vitamin D3 promotes the absorption of calcium, while vitamin K2 contributes to the maintenance of normal bones and to normal blood clotting. The two complement each other, and the Vitamin D3 2000 + K2 formula brings them together in a single softgel. If you take blood thinners, discuss it with your doctor first.
If your priority is calcium intake itself, for example after the age of fifty, the Calcium & Vitamin D chewable tablet combines 1000 mg of calcium with vitamin D3, with both contributing to the maintenance of normal bones.
When to start and how long to continue
September is a good moment to begin, before your summer reserves run out. Most people continue their course until March or April and then taper off as the days get longer. The simplest approach is to take your capsule every day with the same meal, which makes it easier to remember.
In short
Vitamin D deficiency affects a large part of the Belgian population, for a reason that has little to do with diet: our latitude. Topping up your intake during the dark months is a simple habit, as long as you choose a dose that fits your lifestyle and take it with a meal. If you are unsure, a blood test and your doctor's advice remain the best starting point.
Food supplement. Not to be used as a substitute for a varied diet and a healthy lifestyle.
