Abstract
Currently the best assessment of vitamin D status is the serum concentration of 25-hydroxyvitamin D (25(OH)D). Controversy exists as to what constitutes an adequate serum 25(OH)D concentration; in this literature review a sufficient concentration for all age groups was defined as >50 nmol/L (>20 μg/L).
Vitamin D deficiency, a serum 25(OH)D concentration of <25 nmol/L, is highly prevalent in India and China. It is also common in the Middle-East, where it is often related to clothing. One study found a mean serum 25(OH)D concentration of 32 nmol/L in Turkish females with a veil (hijab), while it was only 9 nmol/L in women who were completely covered with niqab. In Mongolia the prevalence of rickets was as high as 70%.
Within Europe vitamin D status is usually better in the Nordic countries than around the Mediterranean, despite sunshine and ultraviolet B exposure being higher in southern European countries. This may be due to a lighter skin, sun-seeking behaviour and a high consumption of cod liver oil in the Northern countries. In the UK the National Diet and Nutrition survey found 15–25% of the adolescent and young adult population tested to be vitamin D deficient: 20–35% of those over 85 y were also found to be deficient.
Overall, studies have shown groups at high risk of deficiency to include the elderly, especially if institutionalized, children, adolescents and young adults. Obesity is also an important determinant, and the trend of increasing body mass index in the Western world may further decrease vitamin D status. Nutrition and supplement use also influence vitamin D status as evident in the USA and Canada, where milk is fortified and the use of vitamin supplements is relatively common.
This review highlights the significance of vitamin D deficiency as a major public health problem worldwide, requiring urgent attention.