Vitamin D Adequacy Conditions the Prolactin-Suppressive Effect of Metformin in Men Receiving Prolactin-Elevating Medications

This study examined the role of vitamin D status in the prolactin-lowering effect of metformin in 75 men with antipsychotic-induced hyperprolactinemia and type 2 diabetes or prediabetes. Participants were divided into groups based on their vitamin D levels. Over six months, metformin improved glycemic control and insulin sensitivity in all groups, with more significant effects in those with adequate vitamin D. Notably, prolactin levels decreased only in men with sufficient vitamin D, indicating that vitamin D adequacy is crucial for metformin's prolactin-suppressive effects. The study suggests that assessing and correcting vitamin D levels could enhance metformin's efficacy in managing hyperprolactinemia in this population.