Vitamin D in obesity and obesity-related diseases: an overview

Hypovitaminosis D and obesity represent two pandemic conditions sometimes associated with each other. Although it is known that there is a close relationship between these two health problems, the underlying pathophysiological mechanism has not yet been fully clarified. In fact, on the one hand, obesity per se seems to involve low circulating levels of vitamin D due to low sun exposure, physical activity, and intake of foods rich in vitamin D, volumetric dilution and sequestration in the adipose tissue. Conversely, since pre-adipocytes and adipocytes express the receptors and are involved in the metabolism of vitamin D it would seem that low levels of this vitamin may be involved in adipogenesis and therefore in the development of obesity. This connection is extremely important when considering obesity-related diseases. In fact, low vitamin D levels and severe obesity are significantly associated with some cardio-metabolic risk factors, including high body mass index, waist circumference, blood pressure, impaired lipid and glycemic profile, and insulin resistance, as they would seem associated with worse cardiovascular outcomes and higher cancer incidence and mortality. Therefore, the purpose of this review is to examine the recent evidence linking low vitamin D status, obesity and obesity-related diseases, highlighting the scientific achievements and the gaps to be filled with further investigations.