Fitness supplements are usually based on the improvement of muscle mass and sports performance or the reduction of fat mass, but today we are going to talk about supplements that are slightly different, mainly health. Vitamin D, also known as "sunshine vitamin", is a common vitamin supplement in the market. You must have heard the doctor say that everyone needs vitamin D supplementation. Vitamin D is a fat-soluble essential vitamin. Fat solubility means that it must be eaten with fat to be absorbed.

It is called "sunshine vitamin" because the skin can secrete vitamin D under sunlight. Although the body itself can produce vitamin D, its main source is food, such as fish, eggs and dairy products, because modern people live indoors, and the ultraviolet index of sunlight is high enough for the body to produce vitamin D itself. In addition, the closer to the equator, the whiter the skin, and the higher the synthesis rate of vitamin D.

The study found that in winter, the population's vitamin D deficiency rate is very high. In some northern countries, such as Estonia, at the end of winter, the number of people with insufficient vitamin D content is as high as 73%. But even in some countries near the equator, such as Iran, the proportion is 50.8%.