Vitamin D levels

Vitamin D is an essential nutrient for the maintenance of our health. Its main function is the regulation of calcium and phosphate levels, so it has a nutritional role in the maintenance of healthy bones and teeth.

Vitamin D is produced in the human skin from 7-dehydrocholesterol by the action of UVB rays. This vitamin D is biologically inactive and needs to be metabolized to produce different compounds that are active and responsible for multiple functions in the body.

When UV rays come into contact with the skin, 7-dehydrocholesterol is transformed into cholecalciferol or vitamin D3. This, which is actually a prohormone, is biologically inactive. To be functional, it must undergo two transformations, the first in the liver forming calcidiol or 25-hydroxycholecalciferol and the second in the kidney forming calcitriol or 1-alpha-25-hydroxycholecalciferol which is the active form.

The main function of vitamin D is the regulation of calcium and phosphorus homeostasis, however, in recent years, many other unrelated functions have been identified in the immune, endocrine, neuromuscular or hematopoietic systems. Beneficial effects of vitamin D consumption have even been observed in some diseases such as rheumatoid arthritis or multiple sclerosis.

The vitamin D needed by the body comes from two sources: synthesis in the skin in the presence of sunlight and the intake of foods that contain it. In the human species, the main source is skin synthesis and a smaller proportion depends on food. However, there are external agents that can hinder this cutaneous synthesis, such as latitude, advanced age and dark-colored skin, and in these cases it is important to guarantee an adequate intake.

There are very few foods that contain vitamin D naturally, being fatty fish such as salmon or trout the richest in this compound, in addition to fish liver oil which is the richest source. Nowadays, we can find many foods fortified with vitamin D.

Vitamin D blood levels are determined by vitamin D metabolism. This metabolism, in turn, can be altered by different variants that can affect its efficacy, so that, in addition to being affected by environmental factors such as diet, inherited markers can also affect this trait. Through a GWAS study of more than 300,000 participants from different geographic ancestries, 39 markers associated with vitamin D levels have been identified. Among the genes identified, we can find the GC or BDP gene, which produces a protein that binds to the different forms of vitamin D to allow its transport, or the KRTAP5-7 gene, involved in the production of keratin and keratinocytes in the skin, where the transformation of cholesterol metabolites into inactive forms of vitamin D occurs, which continue their metabolism until they are transformed into the active and functional forms of this vitamin.

Number of observed variants

13.5 million variants

Number of loci analyzed in the study

39 loci


Sinnot-Armstrong N, Tanigawa Y, et al. Genetics of 35 blood and urine biomarkers in the UK Biobank. Nature Genetics, 18 Jan 2021, 53(2):185-194

National Library of Medicine (NIH). Office of Dietary Supplements [April 2022]

National Health Service in England (NHS). Vitamin D [August 2020]

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