Epidemiological studies reported that
vitamin D deficiency represents an increasingly widespread phenomenon in various populations.
Vitamin D deficiency is considered a clinical syndrome determined by low circulating levels of
25-hydroxyvitamin D (25(
OH)D), which is the biologically-inactive intermediate and represents the predominant circulating form. Different mechanisms have been hypothesized to explain the association between hypovitaminosis D and
obesity, including lower dietary intake of
vitamin D, lesser skin exposure to sunlight, due to less outdoor physical activity, decreased intestinal absorption, impaired hydroxylation in adipose tissue and 25(
OH)D accumulation in fat. However, several studies speculated that
vitamin D deficiency itself could cause
obesity or prevent
weight loss. The fat-solubility of
vitamin D leads to the hypothesis that a sequestration process occurs in body fat depots, resulting in a lower bioavailability in the obese state. After investigating the clinical aspects of
vitamin D deficiency and the proposed mechanisms for low 25(
OH)D in
obesity, in this manuscript we discuss the possible role of
vitamin D replacement treatment, with different formulations, to restore normal levels in individuals affected by
obesity, and evaluate potential positive effects on
obesity itself and its metabolic consequences. Food-based prevention strategies for enhancement of
vitamin D status and, therefore, lowering skeletal and extra-skeletal diseases risk have been widely proposed in the past decades; however pharmacological supplementation, namely
cholecalciferol and
calcifediol, is required in the treatment of
vitamin D insufficiency and its comorbidities. In individuals affected by
obesity, high doses of
vitamin D are required to normalize serum
vitamin D levels, but the different liposolubility of different supplements should be taken into account. Although the results are inconsistent, some studies reported that
vitamin D supplementation may have some beneficial effects in people with
obesity.