The Impact of Sex and 25(OH)D Deficiency on Metabolic Function in Mice.

Both dietary fat and vitamin D deficiency have been linked with increased incidence of non-alcoholic fatty liver disease and insulin resistance. While sex differences in disease prevalence and severity are well known, the impact on disease pathogenesis remains unclear. To further explore the effect of these exposures on metabolic function, C57BL/6 male and female mice were weaned onto one of four diets; low fat vitamin D replete, low fat vitamin D deficient, or two high fat diets, one vitamin D replete and one deficient. Visceral fat, hepatic adiposity, and insulin resistance were measured after five and a half weeks. Vitamin D deficiency, independent of dietary fat, increased hepatic fat accumulation in both sexes (p = 0.003), although did not increase hepatic expression of interleukin-6 (p = 0.92) or tumor necrosis factor-α (p = 0.78). Males were observed to have greater insulin resistance (glucose area under the curve: p < 0.001, homeostatic model assessment for insulin resistance: p = 0.046), and have greater visceral adiposity (p < 0.001), while female mice had greater hepatic fat accumulation (p < 0.001). This study is the first to demonstrate vitamin D deficiency alone can cause hepatic accumulation while also being the first to observe higher liver fat percentages in female mice.