[Epidemiology of vitamin-D deficiency]

The 25-hydroxyvitamin D (25OHD) serum concentration is the consensual marker of vitamin D status. In the general population, the Institute of Medicine considers that a 25OHD level >20 ng/mL is sufficient for bone health in most subjects. In osteoporosis patients, in those who have a pathology or who receive drugs that may increase the risk of osteoporosis, as well as in patients with chronic kidney disease, many experts think that an optimal vitamin D status is better defined by a 25OHD concentration >30 ng/mL. In the French general population, 43-50% of subjects have a 25OHD level <20 ng/mL and approximately 80% have a 25OHD <30 ng/mL. In chronic diseased patients, as well as in some categories of the general population such as elderly people, the percentage of subjects with a 25OHD level below 20 ng/mL is frequently well above 50%. Epidemiologic studies allow us to identify risk factors for vitamin D deficiency such as ageing, overweight, dark skin pigmentation, wearing covering clothes, or having a low level of outdoor activity. This will help to target vitamin D supplementation to "at-risk" subjects. However, discussions on means to improve the vitamin D status of the overall population such as allowing higher levels of food fortification, are needed.