In recent months, with the spread of the Covid-19 epidemic, we have heard a lot about vitamin D because of its multiple physiological functions, including a significant role in regulating the immune system, as well as in bone metabolism. The need for adequate levels of vitamin D underlines the importance of having an adequate weight, a targeted diet and above all a correct lifestyle that includes correct sun exposure (and physical activity in the open air).
The actions of vitamin D are to be attributed to its active metabolite, 1,25-dihydroxycholecalciferol [1,25 (OH) 2D3 or calcitriol], produced thanks to various enzymatic steps, starting from cholecalciferol or vitamin D3, depending on the exposure to the sunlight. In fact, the diet is not the main source of vitamin D, as the amount of calciferol deriving from food is very low and most of the vitamin is synthesized in the skin by the action of ultraviolet light.
The main foods rich in vitamin D3 are the fattest marine fish (especially salmon, sardines, herring and cod liver oil), liver, egg yolk and mushrooms (shiitake), as well as milk, whole yogurt and fatty cheeses.
Vitamin D is a fat soluble vitamin and is absorbed in the intestine (duodenal and jejunal) and distributed to the adipose tissue, from which it is subsequently released in small quantities. An excess of fat mass “traps” vitamin D, which is why the lack of vitamin D is higher in obese subjects.
It should be specified that vitamin D status is classified as follows:
- sufficiency:> 30 ng / ml (> 75 nmol / L)
- insufficiency: 21-29 ng / ml (51-74 nmol / L)
- deficiency: <20 ng / ml (<50 nmol / L)
Hypovitaminosis D is an extremely common condition, as it affects up to 50% of the general population during the winter months in the northern hemisphere. The chances of hypervitaminosis D (overdose of vitamin D), through the diet or through properly taken and formulated food supplements, is remote. Hypovitaminosis D, not only can result in lower bone mineral density and an increased risk of reduced bone density (osteoporosis) or bone fractures, but can also influence the regulation of the immune response.
In light of the role of the hormone in our body, it is essential that the serum levels of vitamin D are adequate. The lockdown of the previous months has significantly reduced sun exposure, exacerbating the risk of vitamin D deficiency. Hence the importance of taking advantage of the summer season for correct sun exposure, in the less hot hours, even better while practicing physical activity outdoors. Although the ideal sun exposure times may depend on the season, the skin and various other factors, sun exposure of at least 15 minutes a day could be a good practice to add to the behaviors implemented within one healthy lifestyle.