When the number of hours of sunlight decreases in winter, we also produce less vitamin D. Is this a problem?
Every year, when the days get shorter and it’s dark outside when you leave the office, the vitamin D report is triggered again. Vitamin D is an important building block for functions such as bone and tooth formation, as it ensures that our bodies can absorb calcium. It also strengthens the immune system and regulates the production of the happiness hormones serotonin, dopamine and noradrenaline.
It is the only vitamin that our body can produce on its own. Strictly speaking, vitamin D is not actually a vitamin at all, but a hormone. Our bodies need sunlight to make it: When UVB rays hit our skin, they make vitamin D. In order to make enough vitamin D, our skin needs to be exposed to the sun for a period of time without protection. Even SPF 20 sunscreen inhibits vitamin D production.
We can also cover a smaller part of the need with food, but this source is only 10 to 20 percent compared to the skin. There are also relatively few foods that are really high in vitamin D. These are mainly fatty fish such as salmon, trout or tuna, but avocados, eggs and some mushrooms such as boletus or mushrooms also have above-average amounts of vitamin D. And we’d have to eat a lot of it to get enough vitamin D. As an example: You’d have to eat two servings of oily fish a day to meet your needs.
How much vitamin D do we need?
So how do we get enough vitamin D? According to the Federal Office of Public Health, 10 minutes of sunbathing on the face and hands several times a week in the summer is enough for people with little skin pigmentation to create the daily requirement of vitamin D. For people with more skin pigmentation, 20 to 60 minutes. Ideally in the morning or afternoon when the sun is not so strong. And of course, you should only expose your skin to the sun unprotected long enough to avoid burning and damage.
However, the problem is that in our latitudes, the hours of sunlight are too short in winter and the intensity of UV rays too low to produce enough vitamin D. In summer, we can stock up on vitamin D because the excess is stored in fat and muscle tissue , which we can return to in the winter. However, for many it is not enough until spring. Studies show that in the winter months the level of vitamin D in the Swiss population is often below the recommended value.
Vitamin D deficiency
When is there a shortage?
According to the Federal Office of Public Health (BAG), there is a vitamin D deficiency if the concentration of 25-hydroxyvitamin D (vitamin D precursor) in the blood is below 50 nanomoles per liter. If this value is less than 25, there is a serious deficiency. Even on the basis of these values, however, it is difficult to determine the defect, because they correspond to the annual average. Because we produce more vitamin D in the summer and less in the winter when there is less sunlight, these values naturally fluctuate without us having any symptoms of deficiency. It is therefore controversial in professional circles when exactly vitamin D deficiency occurs.
What are the consequences of deficiency?
If signs of vitamin D deficiency appear – in adults, this can be bone or muscle pain, muscle weakness or general fatigue – it makes sense to consult a doctor. Because severe vitamin D deficiency can have negative effects on bone health and muscle strength; in children, bone growth disorders and skeletal deformities may occur. In addition, deficiency in old age may contribute to the risk of osteoporosis. People who are hardly exposed to sunlight, for example due to a chronic illness, are particularly affected.
This in itself may not indicate a serious defect. Nevertheless, especially in winter, many take preventive vitamin D supplements. There are various products on the market from effervescent tablets, drops or fortified foods such as margarine or milk products. In Switzerland, these can contain a maximum of five micrograms in a daily portion. An adult has a daily need of 15 micrograms, over 60 20 micrograms. As long as this is not exceeded, vitamin D supplementation is generally harmless.
When are vitamin D supplements useful?
Supplementation is not necessary for everyone. The Federal Food Safety and Veterinary Office generally recommends vitamin D supplements for people over age 60 because the skin’s ability to produce vitamin D declines with age. Vitamin D supplements are also recommended for infants under one year of age after consulting a doctor, as children of this age should not be exposed to sunlight without protection. In healthy older children and adults, supplementation is recommended if there are signs of deficiency despite sun exposure and a diet rich in vitamin D.
Experts still disagree on whether vitamin D supplements are really effective. Various studies in recent years have not been able to demonstrate vitamin D drops and other supplements have a clear effect on all the positive effects that the vitamin is said to have. For example, their intake failed to clearly reduce the risk of bone fractures or cardiovascular disease in older people.
In any case, it is important to follow the recommended dosage. Because excess vitamin D is stored in tissue, excessive intake can lead to symptoms of poisoning. This happens especially when, for example, preparations and fortified foods are consumed at the same time. Overdose can lead to nausea, vomiting and loss of appetite and, in the worst case, to kidney damage or cardiac arrhythmia.