Vitamins play a central role in the body. However, the body cannot produce them itself. Therefore, vitamins must be continuously supplied in sufficient quantities through food, the sun (in the case of vitamin D), or at least through supplementation. In winter, however, the days are shorter; the days are usually spent indoors in frosty temperatures, and vitamin D suppliers are therefore reduced. So, how do we replenish our vitamin D stores without the sun to stay healthy?
As we all know, the sun is in short supply in the winter. From October to March, not enough UV-B radiation reaches the earth’s surface in our latitudes for the body’s own relevant production. Vitamin D can be stored in fatty tissue and muscles for months. However, most people do not manage to recharge their stores sufficiently over the summer months. This is because a large part of life occurs in closed offices and on public transport, even in the warmer months. This is why 95 percent of all Europeans suffer from a vitamin D deficiency during the darker months.
Can we produce vitamin D from the sun’s rays shining through the window?
Unfortunately, we can’t get vitamin D through the window. Michael Holick, professor at the Boston University School of Medicine, emphasizes to the New York Times that it makes no difference whether it is winter or summer: “If you sit behind the window, no vitamin D is produced.” The body’s own production of vitamin D requires UVB rays. These rays are absorbed by the sun in the skin and converted into vitamin D. However, if there is a pane of glass between us and the sun, the UVB rays are filtered out.
How much vitamin D do I need?
How much depends on several factors: Skin color, for example, plays a significant role. The darker your skin, the more sun you need. Age is also a decisive factor. This is because the skin’s ability to produce vitamin D decreases by up to 70 percent over the years. There is also an increased need during pregnancy and breastfeeding. A deficiency can manifest itself in numerous symptoms – however, these are extremely unspecific and are, therefore, often not recognized or misinterpreted. Signs include frequent infections, constant fatigue and tiredness, bone and back pain, depression, poor wound healing, brittle bones, hair loss, muscle cramps, and pain.
Am I undersupplied?
Your family doctor can carry out a blood test to determine your deficiency. As part of this check-up, doctors can determine whether and how much vitamin D should be taken as supplements. A 1-25 ng (nanograms)/ml of blood is considered a severe deficiency; 25-35 ng/ml describes an undersupply. A truly optimal supply is only given in the range between 40 and 60 ng/ml.
What is the best way to take it?
If the vitamin D requirement cannot be covered by the body’s own vitamin D production in the skin, it is important to fall back on alternative sources. A small but very important contribution to covering the requirement is made by nutrition, for example, through:
Incidentally, the food richest in vitamin D is cod liver oil. This is why it used to be given to children as a preventative measure against rickets (a disease of the growing bones associated with vitamin D deficiency). Nowadays, the extra spoonful of brown-yellow oil is no longer necessary. Vitamin D is now available in the form of food supplements. Studies recommend a daily intake of vitamin D supplements (the dose should ideally be prescribed by the doctor treating you). As vitamin D is one of the fat-soluble vitamins, nuclear medicine specialist Prof. Jörg Spitz (author of “Vitamin D Deficiency”) recommends taking it together with a portion of fat to trigger fat absorption in the intestine, regardless of whether the food supplement is oil-based or not.
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