Hypogonadism, a disorder in which dysfunction of the ovaries or testes results in the diminished production of sex hormones, is a growing concern, demonstrated by a marked increase in prescriptions for testosterone replacement. Previous research has reported lower serum testosterone in males with type 2 diabetes and metabolic disease. To expand on this observational research, investigators aimed to determine the effects of a glucose challenge on testosterone levels.

Testosterone levels change in response to food intake, which activates the secretion of messenger molecules from the hypothalamus that affect the reproductive organs. While some studies have reported a decrease in serum testosterone in response to glucose intake, others have found an increase in serum testosterone in response to a dose of insulin. The mechanisms underlying the relationship between glucose intake and testosterone levels have yet to be illuminated.

The authors conducted their investigational study with a group of 74 healthy males (19 to 74 years old) of varying weight status who had not been diagnosed with type 2 diabetes. The researchers administered an oral glucose tolerance test in which participants consumed 75 grams of glucose, which is roughly the amount of sugar in two cans of sugar-sweetened soda, and had their blood drawn before consuming the glucose (baseline) and at 30, 60, 90, and 120 minutes afterward. The researchers also collected blood for the measurement of testosterone and other hormones, including luteinizing hormone, which stimulates testosterone production.

At baseline, 57 percent of the participants had normal glucose tolerance, 30 percent had impaired glucose tolerance, and 13 percent met the criteria for a diagnosis of type 2 diabetes. Glucose intake resulted in lower serum testosterone at all time points following glucose consumption, with an average maximum decrease of 25 percent from baseline levels. The authors reported no changes in plasma concentrations of luteinizing hormone or cortisol and a significant decrease in plasma levels of the hormone leptin. Finally, they reported no differences in testosterone response between men of varying glucose tolerance or weight status.

The investigators concluded that a challenge of 75 grams of glucose significantly decreased serum testosterone levels, although the mechanisms that drove the decrease are still unclear, given that no changes in luteinizing hormone were found.

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