Effect of Oral Vitamin D Overdose in Male and Female Wistar Rats with Induced MASLD

Background/Objectives: Vitamin D is recognized as a key modulator of metabolic diseases, including metabolic-dysfunction-associated steatotic liver disease (MASLD), in which its deficiency contributes to both disease onset and progression. Despite the widespread and often prolonged use of vitamin D supplementation, optimal serum levels in individuals with MASLD remain unclear and warrant further investigation. Methods: In this study, hepatic steatosis was induced in male and female Wistar rats over a 45-day period. The animals were then divided into five groups (control, 2500, 7000, 14,000, and 21,000 IU/kg/week of cholecalciferol). After four weeks of treatment, the animals were euthanized, and blood samples were collected for biochemical, hormonal, inflammatory, oxidative stress analyses and liver architecture evaluation. Results: High-dose vitamin D supplementation in rats with MASLD induced dose-dependent metabolic, inflammatory, and oxidative changes, with some sex-specific differences. Urea and alanine aminotransferase levels increased at higher doses in both sexes, suggesting potential nephrotoxic and hepatotoxic effects, while creatinine and aspartate aminotransferase remained stable. Adiponectin levels decreased consistently, and leptin levels rose across all doses, indicating a shift toward a pro-adipogenic profile. Pro-inflammatory molecules (IL-1β, IL-6, IL-8, TNF, C-reactive protein) increased progressively with dose, while IL-10 followed a U-shaped curve. Oxidative stress markers showed elevated protein carbonylation only at the highest dose, a slight reduction in TBARS, and a peak in total antioxidant status at 7000 IU/kg/week. Conclusions: High-dose vitamin D triggers antioxidant responses but drives harmful inflammatory and metabolic shifts in MASLD.