Potential role of vitamin D in prevention of skeletal and extraskeletal diseases in older people

Vitamin D and calcium are essential for bone health. An adequate calcium-phosphorus product determines a high quality mineralization long lifetime. In older people, both calcium and vitamin D levels may be lower causing osteomalacia and/or osteoporosis with a higher risk of fracture. Epidemiological data have clearly associated serum vitamin D lower levels (deficiency) with bone fracture in older people, however, not univocal data exist in regard to a beneficial effect of vitamin D supplementation in general population. Although not systematic, the present review aims to make a narrative synthesis of the most recent published data on vitamin D effect not only on bone, classical target associated with vitamin D studies, but namely on extraskeletal diseases. In fact, recently, there has been an increasing interest on this latter issue with surprising findings. Vitamin D, and in particular its deficiency, seems to have a role in pathophysiological pathways in several diseases involving cardiovascular, central nervous system and neoplastic process. On the other hand, vitamin D supplementation may modify the outcome of a wide range of illnesses. Up to date the data are conflicting mainly because of difficulty to establish a consensus on the threshold of vitamin D deficit. The US Institute of Medicine recommends to distinguish a level of insufficiency [defined as 30-50 nmol/L or 16-25 ng/mL of 25(OH)D] and another of deficiency identified by 25(OH)D levels lower than 30 nmol/L (or <16 ng/mL). This latter level is considered a minimum level necessary in older adults to minimize the risk of falls, fracture and probably to have some effects of vitamin D supplementation in extraskeletal diseases. Although there are no absolute certainties in such issue, the most recent data suggest that vitamin D deficiency, and its supplementation, may play an important role in a wide range of diseases other than in bone metabolic diseases in older but not in general population. For such reason a widespread measurement of vitamin D levels in general population, and not only in older, seems to be inappropriate and it could induce an overuse of vitamin D supplementation in situations in which its efficacy and cost-effectiveness have not been proven.