Using oral metformin for 1 month may decrease serum testosterone levels independent of blood glucose control in men with type 2 diabetes (T2D), according to the results of a study published in Diabetes Care.

Men with T2D are known to frequently present with low testosterone levels, yet the effect of metformin, the most prescribed oral medication for T2D, on the testosterone levels of men with T2D has not yet been established.

To evaluate the effect of metformin on the testosterone levels of men with T2D, data from 70 men recently diagnosed with T2D were analyzed. Individuals aged 18 to 60 years were included if they had an HbA1C greater than 9.0% and had not received lipid-lowering or antihypertensive treatment.


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Participants began taking metformin after insulin pump treatment normalized blood glucose levels, which took approximately 3 to 5 days. 50% of the participants were randomly assigned to receive metformin in addition to intensive insulin treatment. Serum testosterone levels were measured at baseline, at the point of randomization, and again after 1 month of treatment.

Total, free, and bioavailable testosterone increased significantly after the normalization period in all patients (P <.001). However, after 1 month of treatment, a significant decrease in total, free, and bioavailable testosterone was observed in the metformin group compared with baseline levels (P <.05). No significant decrease was observed in the control group.

The results of this study indicated that 1 month of metformin treatment was associated with significantly lowered testosterone levels in men newly diagnosed with T2D. Additionally, this study showed that a 5-day period of intensive insulin therapy to normalize blood glucose levels also increased testosterone significantly in men recently diagnosed with T2D.

These results may be useful for physicians who wish to maintain normal testosterone levels in newly diagnosed T2D patients.

Limitations to this study include its short duration and its lack of data on insulin resistance.

Future research investigating the long-term impact of metformin treatment on testosterone levels is warranted to determine if results are independent of blood glucose and weight change.  

Reference

Hu Y, Ding B, Shen Y, et al. Rapid changes in serum testosterone in men with newly diagnosed type 2 diabetes with intensive insulin and metformin. Diabetes Care. Published online February 2, 2021. doi:10.2337/dc20-1558