Vitamin D supplementation improves fasting insulin levels an
Vitamin D has been linked with glucose and lipid metabolism. Men with impaired gonadal function have a higher risk of metabolic syndrome and mortality, and vitamin D status may be a reversible modulator.

This study aimed to determine the effect of daily vitamin D and calcium supplementation for 150 days on glucose and lipid homeostasis in infertile men.

A single-center, double-blinded, randomized clinical trial, 307 infertile men were randomized (1:1) to a single dose of 300,000 IU cholecalciferol followed by 1,400 IU cholecalciferol + 500 mg of calcium daily (n=151) or placebo (n=156) for 150 days. Reported metabolic parameters including fasting plasma glucose, HbA1c, fasting serum insulin, homeostatic model assessment of insulin resistance (HOMA-IR), fasting plasma cholesterols and triglyceride were secondary endpoints. The primary endpoint semen quality has previously been reported.

-- Men receiving vitamin D supplementation improved their vitamin D status, while vitamin D status was aggravated in the placebo group characterized by higher serum parathyroid hormone (PTH).

-- At end of trial, men receiving vitamin D supplementation had 13% lower fasting serum insulin concentrations compared with the placebo-treated group (65 vs. 74 pmol/L) and 19% lower HOMA-IR (2.2 vs. 2.7).

-- Moreover, men in the vitamin D group had higher high-density lipoprotein (HDL) cholesterol levels (1.38 vs. 1.32 mmol/L) compared with the placebo group.

Conclusively, high-dose vitamin D supplementation had beneficial effects on glucose homeostasis and HDL cholesterol levels in infertile men.