Vitamin D deficiency is characteristic of type 2 diabetes (T2D) due to urinary excretion of 25-OH vitamin D3 (25D), the major circulating form of vitamin D that is reflective of vitamin D status. We have previously shown that whole eggs, a rich dietary source of vitamin D, can increase circulating 25D concentrations in T2D rats. Thus, the aim of this study was to compare vitamin D derived from consuming whole eggs versus a dietary supplement of vitamin D3 (i.e. cholecalciferol) in T2D. Zucker diabetic fatty rats (ZDF) (n=24) and their lean controls (n=24) were randomly assigned to one of three diets: an AIN93 casein-based diet, a whole egg-based diet, or an AIN93 casein-based diet containing supplemental vitamin D3 at the same level of total vitamin D provided by the whole egg (37.6 μg/kg diet). Protein was provided at 20% (w/w) of the diet by either casein or whole egg. All diets were matched for lipid content (18.3%) via the addition of corn oil to the casein-based diets to account for the additional lipid contribution of the whole egg. All rats were placed on their respective diets for 8 weeks. Mean values from all analyses were compared using a one-way ANOVA (P<0.05). As expected, casein-fed ZDF rats gained more weight than all of the lean rats; however, ZDF rats fed a whole egg-based diet exhibited an 18% decrease in weight gain compared to the ZDF-casein groups. Although ZDF rats fed the whole egg-based diet gained less weight than ZDF rats fed the casein-based diets, food intake did not differ within a given genotype. As expected, ZDF rats fed the casein-based diet had lower (21%) serum 25D concentrations than their lean casein-fed counterparts. An egg-based diet fed to the ZDF rats was highly effective at increasing serum 25D concentrations by 130% compared to casein-fed ZDF rats. In contrast, supplemental vitamin D3 also increased circulating 25D concentrations in the ZDF rats fed casein, but only by 35%. Likewise, serum 25D concentrations of lean rats fed the supplemental vitamin D3 diet and the whole egg-based diet were increased by 19% and 113%, respectively, compared to lean rats fed the casein-based diet. These data demonstrate that, at an equal dietary vitamin D concentration, whole egg consumption was markedly more effective at maintaining serum 25D concentrations than supplemental vitamin D3 in both the lean and ZDF genotype.
