Vitamin D is obtained from food sources in the form of vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). The latter can also be obtained from skin synthesis by sun exposure. When sunlight hits the skin, cholesterol produces vitamin D. Exposing the face and arms to the sun for about 15 minutes a day, avoiding sunburn, is sufficient to achieve adequate production of vitamin D.

Normally, vitamin D reserves do not last all winter. In addition, at Northern latitudes the sunlight is not intense enough at this time of year to produce enough vitamin D. Therefore, people who do not leave their homes or those who dress themselves covering their entire skin are at especially high risk of suffering from vitamin D deficiencies.

The same is true for dark-skinned people, since pigmentation reduces the UV radiation that reaches the cells that produce vitamin D. The frequent and rigorous use of sunscreens, usually recommended to protect us from skin cancer, also blocks the synthesis of vitamin D. Therefore, vitamin D from food sources plays a very important role. Therefore, people with a normal diet and who go out enough to the streets should not worry about the amount of vitamin D they must absorb.

More than 80% of coronavirus patients are vitamin D deficient and this deficiency is more common in men, according to a study published in the Journal of Clinical Endocrinology & Metabolism.

The patients with covid-19 in this retrospective work were patients from the Hospital Universitario Marqués de Valdecilla in Santander (Spain). A total of 216 cases were studied.

What causes their deficiency and how much do I need?

Vitamin D is a fat-soluble vitamin needed to maintain good bone and tooth health. It is involved in the absorption of calcium and phosphorus from food, and participates in the good structure on which bone tissue can develop. It also serves to stop osteoporosis, intervening in the maintenance of resistance and muscle function.

The need for vitamin D is difficult to quantify because it depends on sun exposure and skin pigmentation. For the adult population the needs are around 10 µg per day (these levels increase in the case of pregnant and lactating women).

A lack of vitamin D produces hypocalcemia (lack of calcium) and, consequently, a poor mineralization of the bones. Therefore, infants, young children, pregnant women and the elderly represent population groups at risk because they may suffer from a deficiency of this vitamin because their exposure to sunlight is insufficient or because their requirements are increased (in the case of pregnant women).

Foods with Vitamin D

The main sources of this liposoluble vitamin, besides the exposure to the sun, are the fatty fish, the whole milky and eggs so, once again it is necessary to return to the Mediterranean pattern:

Food Portion size 100 g Portion
Tuna in oil 60 g 25 µg 15 µg
Smoked salmon 75 g 19 µg 14,25 µg
Salmon 125 g 8 µg 10 µg
Chicken egg 1 unit (55 g) 1.75 µg 1 µg
Whole milk 1 glass (200 ml) 0,25 µg 0,5 µg


As we see, foods with vitamin D, therefore, those that are naturally richer in this vitamin are fatty fish: do not lack in your diet.

Supplementation is not always an advantage

Several studies have shown that the risk of suffering from a deficit in vitamin D is real, and to this situation some manufacturers have reacted and started to fortify their products. One example is some breakfast cereals enriched in this vitamin. These products are a help, but we must not lose sight that along with this “extra” vitamin D, other nutrients are ingested that are not as beneficial as added sugars, salt or saturated fats.

As we have already seen, vitamin D accumulates easily in the body (in the liver and in the fat reserves) and, as a consequence, it can produce a possible “poisoning”. The symptoms of an overdose are nausea, vomiting, diarrhea, pain, tiredness and kidney problems. The toxic effect is produced when an intake higher than 100 µg per day is prolonged in the adult population (50 µg in children under 10 years). The intense solar exhibition can cause burns and other dermatological injuries, but not an excess of vitamin D, that can only derive from an exaggerated ingestion of foods that contain it and, mainly, of vitamin supplements.


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