Vitamin D is not only a key component in the maintenance of
calcium homeostasis and bone health, but has also been implicated in a myriad of other non-skeletal
biologic systems. The
frailty syndrome is an emerging and increasingly important concept in the field of aging, with the "physical" clinical phenotype being initially presented as the operational definition. The relationship between
vitamin D and
frailty is postulated to be largely mediated via the development of
sarcopenia, a condition characterised by a combination of the reduction of muscle mass, plus either muscle strength or performance. Several molecular pathways may account for the development of muscle wasting in
sarcopenia, and there is mounting epidemiological and laboratory evidence that supports a role of
vitamin D on muscle cell proliferation and function. Although observational studies on
vitamin D and
frailty have not definitively established an independent relationship, interventional studies of the effect of supplemental
vitamin D have yielded a positive influence on the
frailty status, mainly via improvements in the physical performance. Further studies that are adequately powered and well-designed are warranted in an attempt to establish a causal relationship between
vitamin D and
frailty. In the absence of a consensus on the definition of the
frailty syndrome, an appropriate and well-validated measure instrument for this health outcome would be recommended in the realm of
frailty research.