Vitamin D, also called the "sunshine vitamin," is known for its role in bone health. In recent years, it has aroused great interest in research due to its health-promoting properties.

Vitamin D is a vitamin —an organic compound that works as a micronutrient whose intake is necessary— and a pro-hormone that is synthesized in the skin through sun exposure and afterward transformed in the body, becoming a real hormone with physiological actions in the body.

Can we get vitamin D only from sunlight?

Vitamin D exists in two forms: vitamin D2 or ergocalciferol, which is found in plants and some fungi, and vitamin D3 or cholecalciferol, which is produced in some vertebrates and naturally in the body with sun exposure. Vitamin D is a fat-soluble compound that is stored in fatty tissue.

Sun exposure can account for up to 90% of vitamin D supply. Only 5 to 10% of vitamin D is obtained through foods that contain it naturally, such as blue fish (mackerel, sardines, tuna, salmon), dairy products, some mushrooms, avocado and egg yolk, among others. These foods may help reach the daily requirements of vitamin D, but they are an insufficient source of vitamin D on their own.

Although it is only necessary to expose the skin to the sun for five to ten minutes twice or three times a week to obtain enough vitamin D, several studies show that a part of the world population has a deficiency of this vitamin.

How much vitamin D should we have?

The amount of vitamin D that each of us needs is different and variable. There are some factors that may affect the amount we naturally synthesize:

  • AGE. Our body may produce less vitamin D with age.
  • LATITUDE. Latitude determines the intensity of solar radiation.
  • LIFESTYLE. A sedentary lifestyle (just going from home to the office and from the office to home) means that when we go outdoors for a walk or do sport, the sun is no longer shining.
  • SKIN COLOR. The darker the skin color, the slower the synthesis of vitamin D3 by UV radiation.

For some of these reasons, in Spain, despite being a country with many hours of sunlight and being relatively close to the equator, the deficiency of vitamin D is increasingly frequent in the population, which may influence the appearance of other health disorders such as osteoporosis, muscle weakness, depression and even the risk of cancer, among others.

Vitamin D deficiency and supplementation should always be controlled by health professionals, as it is a vitamin that is stored in our bodies, and excess may cause health disorders.

Why is vitamin D essential?

Although it is usually associated with bone maintenance, it has other relevant properties for our bodies regarding not only bones and muscles but also the immune system, glucose, skin and even the central nervous system.

One of the most important functions of vitamin D is the maintenance of calcium and phosphorus in the blood at a suitable rate, as it ensures bone growth, the maintenance of bone density, proper muscle function, healthy teeth and the functioning of the nervous system. Vitamin D increases the intestinal absorption of calcium and its reabsorption in the kidneys, and when the levels are not enough, it mobilizes the calcium stored in the bones. Vitamin D also regulates the absorption of phosphorus in the body.

These are other functions for which the involvement of vitamin D is being studied:

  • Functioning of the nervous system. It is involved in immune function by strengthening our defensive system and helping prevent infections. The potential effects that it may have on COVID-19 are being studied currently, although it is a recent topic on which there is still no consensus.
  • Skin. Its effect on some skin disorders such as acne, pinkish, healing, psoriasis, alopecia, vitiligo or atopic dermatitis is also being studied, as it is a vitamin that is synthesized in the skin and related to the immune system. It has been noticed that patients with vitamin D deficiency tend to present more serious or worsening symptoms than people with a normal level.
  • Cardiovascular system. The possible effects of vitamin D on regulating blood pressure and protecting against other cardiovascular diseases are also under research.
  • Sugar regulation in bloodIt regulates insulin secretion by the pancreas and decreases peripheral insulin resistance. People with vitamin D deficiency have an increased risk of developing diabetes, altered glucose levels in blood and insulin resistance.
  • Nervous system. It has been found that vitamin D has an important role in brain development and function, including neuroprotection, and also helps in the transmission of messages in the nervous system. In addition, vitamin D is associated with poorer performance and a bad mood.

Furthermore, the potential benefits of vitamin D on cancer are being investigated, as it has a role in cell differentiation and proliferation and in both male and female obesity and infertility.

For all these reasons, moderate sun exposure, always protecting the skin properly to avoid damaging it, and a healthy and well-balanced diet that includes foods rich in vitamin D will help us maintain suitable levels of this vitamin in our body.

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