Vitamin D has a crucial role in maintaining normal bone and muscle health, though a significant proportion of the population are deficient. Indeed, in Ireland, 13.1% of the population older than 50 are vitamin D deficient (<30 nmol/l) based on findings from The Irish Longitudinal Study of Ageing (TILDA). In the winter, deficiency affected nearly one in four (24%) with the greatest prevalence (37%) in those aged over 80. Furthermore, about 15% of children and younger Irish adults have been found to be deficient.
Vitamin D is not a nutrient in the traditional sense, but a pro-hormone that is largely derived from cutaneous synthesis after UVB exposure. However, little or no vitamin D synthesis occurs in Ireland between the months of November and March giving rise to the so-called “vitamin D winter”. Dietary sources are limited and contributing only a small proportion to overall levels, but include fortified foods (milks, breakfast cereals), oily fish and eggs. For this reason, low vitamin D status is particularly common in those with limited sun exposure. A significant prevalence of vitamin D deficiency is observed in individuals with darker skin, who require prolonged sun exposure for adequate synthesis due to the presence of melanin. Notably, a study conducted in Ireland found that 67% of Southeast Asians were deficient in vitamin D.
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