Vitamin D deficiency has been linked to the development of osteoporosis and hip fractures as well as to other skeletal and non-skeletal disorders. Beside ‘severe deficiency’ (serum 25-hydroxyvitamin D levels below 25 nmol/liter) and ‘deficiency’ (serum 25(OH)D below 50 nmol/l), there is ongoing debate as to the exact definition of vitamin D ‘insufficiency’– a mild degree of vitamin D deficiency (between 50 and 75 nmol/l).
A 2009 report from the International Osteoporosis Foundation (IOF) shows that regardless of whether insufficiency is defined at 50 nmol/L or 75 nmol/L, vitamin D status is seriously inadequate in large proportions of the population across the globe. The review provides a global perspective of vitamin D status across different regions of the world and identifies common and significant determinants of insufficiency. Six regions of the world were reviewed in a survey of published literature: Asia, Europe, Middle East and Africa, Latin America, North America, and Oceania.
The results showed that depending on the required serum 25(OH)D level, either 50 or 75 nmol/l, the percentage of the population with vitamin D insufficiency is high or very high in most countries.
The main risk factors for low vitamin D levels include older age, female sex, lower latitudes, winter season, darker skin pigmentation, less sunlight exposure, dietary habits, and the absence of vitamin D fortification in common foods. Further factors include the increase in urbanization, where people tend to live and work indoors, as well as cultural practices that tend towards sun avoidance and the wearing of traditional clothing that covers the skin. The severity of the problem in Middle East and South Asia arises from the combination of several of these risk factors.
These findings suggest that prevention strategies must be initiated at the national level – especially given the increasing aging of populations in many regions of the world. National plans of action should encourage safe, limited exposure to sunlight and improved dietary intake of vitamin D, whiles also considering fortification of foods.
For region-specific reports see www.iofbonehealth.org/health-professionals/special-topics/vitamin-d-deficiency.html
Mithal A. et al. on behalf of the IOF Committee of Scientific Advisors (CSA) Nutrition Working Group. Global vitamin D status and determinants of hypovitaminosis D. Osteoporosis International, 2009 (in press).