The effect of diabetes on lowering testosterone levels is similar to a weight gain of 20 pounds, according to new research that finds 40 percent of obese men have below-normal testosterone levels.

As body mass index (BMI) increases, testosterone levels fall even further. BMI is the relationship of weight to height.

“In view of the fact that almost one-third of the U.S. is obese, these observations have profound pathophysiological, clinical, epidemiological, and public health implications,” says Sandeep Dhindsa, an endocrinology specialist at the University at Buffalo and first author of the study published in the journal Diabetes Care.

This is the largest analysis of the association between obesity and low testosterone, and the first to compare prevalence of low testosterone with obesity and diabetes separately and together.

The study shows that obesity and diabetes may exert independent influences on testosterone concentrations.

“We published a report in 2004 on the high prevalence of low testosterone levels in men with type 2 diabetes, and multiple studies all over the world have confirmed the association of low testosterone with diabetes,” Dhindsa notes.

Obesity, like diabetes, also appears to have a negative effect on testosterone levels, according to a new study. “The fact that almost one-third of the U.S. is obese, these observations have profound . . . public health implications,” says Sandeep Dhindsa.

“The Endocrine Society now recommends that all men with type 2 diabetes should have their testosterone levels measured. Our new study shows that obese men also have a very high prevalence of low testosterone levels, so physicians should consider screening obese non-diabetic men, as well, for low testosterone.”

The study was conducted from November 2003 to February 2004 in 95 primary care practices throughout the U.S. involving 2,165 men 45 years or older who provided blood samples for analysis of testosterone concentrations.

“With the rising prevalence of obesity in the U.S. and the rest of the world,” says Paresh Dandona, head of the Division of Endocrinology, Diabetes and Metabolism and senior author of the study, “it is imperative that the prevalence of low testosterone levels in obese men be defined.

“In addition, the magnitude of the contribution of obesity to subnormal testosterone needs to be quantified. We hypothesized that obese men are more likely to have low testosterone than non-obese men, and that we would find more low testosterone levels in men with diabetes than in men without diabetes, both obese and non-obese.”

Results confirmed these hypotheses, showing a 40 percent higher prevalence of low testosterone in obese men compared to the non-obese participants.

Men with diabetes, whether obese or not, showed lower levels of testosterone than non-diabetic men across all weight categories. Testosterone levels decreased significantly in both diabetic and non-diabetic men as BMI increased.

UB researchers excluded participants from the full study who had no BMI data or were on certain drugs that can affect testosterone levels, providing a study population of 1,849 men—398 with diabetes and 1,451 non-diabetics.

“In view of the increasing prevalence of obesity, even in younger populations, it would be important to conduct a similar study in the men at the prime of their reproductive years,” he says.

“In view of the high rates of subnormal testosterone in patients with obesity or diabetes, testosterone concentrations should be measured regularly in these populations, especially when these conditions occur together,” says Dandona.

The work was supported in part by the American Diabetes Association, National Institutes of Health, and Solvay Pharmaceuticals.

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U. BUFFALO (US)