Editorial: Mucus and the mucociliary interface: continuity and clearance.

Vitamin D deficiency affects a large part of the population of elderly people, especially women, who live in moderate climate countries due to a reduced amount of vitamin D in the diet (small sea fish consumption) and reduced content of 7-dehydrocholesterol, which causes decreased skin synthesis. The lowest seasonal concentration of 25(OH)D3 is usually observed during winter and spring. Sun exposure influences 25(OH)D3 concentration more strongly in men than in women. Sociodemographic factors that increase the risk of vitamin D deficiency in the elderly include poor environmental conditions, low economic status, lower educational level, drug exposure (smoking), reduced physical activity, overall poor health and obesity, which causes reduced skin exposure to sunlight. The use of medications or supplements that contain vitamin D and staying in a nursing home that employ such supplementation are factors that prevent deficiency. Significant prevalence of diseases of the gastrointestinal tract may contribute to cholecalciferol and ergocalciferol malabsorption or impair their liver transformation. In addition, the high incidence of chronic kidney disease in old age reduces processing hydroxylation of vitamin D and the formation of active metabolites. Vitamin D deficiency can not only cause bone mineralization disorders, but also increase incidence of cardiovascular diseases, cancers, type 2 diabetes and depression. The aim of this study was to summarize current knowledge about the risk factors of vitamin D deficiency development in the elderly population.