Do Desirable Vitamin D Levels Vary Globally

Vitamin D insufficiency is a common problem worldwide, with a varying prevalence depending on the population of interest and cutoff used to define insufficiency. The medical literature has witnessed an explosion in the number of vitamin D publications over the last three decades, most convincingly supporting a beneficial effect of vitamin D on musculoskeletal parameters. This led the Institute of Medicine (IOM) to issue an update in 2011 with an increase in the recommended vitamin D intake across all age groups and to set the desirable level at 50 nmol/L. This compares modestly to the desirable level recommended by the Endocrine Society (ES) of 75 nmol/L, which is similar to that recommended by the International Osteoporosis Foundation for older individuals. While the IOM Committee focused on the population needs in North America, the Endocrine Society tried to target high-risk populations. Some of the lowest vitamin D levels are recorded in black subjects and in non-western populations, populations in whom data on fractures and falls are scarce. Information using surrogate markers for the beneficial effect of vitamin D action on musculoskeletal health has many limitations, even in Caucasian subjects where it is the most available. The calcium–vitamin D economy in blacks seems different, and the desirable vitamin D level to optimize musculoskeletal health may be lower than that of Caucasians. Furthermore, some evidence from association studies suggests an increase in the risk of fractures in blacks, and possibly Asians, at 25(OH)D levels exceeding the desirable level for Caucasians. In view of this apparent divergence, the lack of solid outcome data in other ethnic and racial groups, and the multitude of modulators that affect vitamin D metabolism and action, the notion of a global desirable vitamin D level to date is not tenable.