Men with lower than normal testosterone appear to have higher fasting insulin levels, but researchers cautioned against overtreatment because men with high testosterone had an adverse blood lipid profile.
Men with low testosterone had insulin measurements of about 6.3 microIU/mL compared with about 5.0 microIU/mL for men with normal testosterone (P=0.003) and about 4 microIU/mL for men with high testosterone (P=0.01), according to Margaret Groves, M.Phil, M.Ed, a researcher with ZRT Laboratories in Beaverton, Ore.
However, men with high testosterone had higher LDL cholesterol (P=0.02) and lower HDL cholesterol (P<0.05), Groves said here at a poster presentation during the World Congress on Insulin Resistance, Diabetes and Cardiovascular Disease.
"What our study showed is that low testosterone is related to insulin resistance in men," she told MedPage Today, "but we also saw that too much testosterone isn't good either."
She encouraged doctors to monitor testosterone -- especially in light of recent advertisements warning men about "low T" -- with either saliva or dried blood spot testing. "These tests can ensure testosterone levels remain in a physiological range for optimum cardiometabolic risk benefits," she said.
"Testosterone supplementation is being increasingly used to help reverse symptoms of metabolic syndrome and improve cardiovascular disease risk in men," Groves noted. "However, data is sparse regarding the direct effects of testosterone levels on cardiometabolic risk markers."
The study Groves and her colleagues conducted to help provide that data enrolled 228 men, excluding those with diagnosed diabetes.
For purposes of the study, they defined low testosterone as less than 300 ng/dl in the dried blood test or less than 4 pg/dl in the saliva test; normal testosterone was defined as in the 300 to 800 ng/dl range with the blood spot test and 40 to 140 pg/dl with the saliva tests; high testosterone was defined as greater than 800 ng/dl with the blood spot tests and greater than 140 pg/dl with the saliva test.
One of the 20 men with low testosterone reported being on testosterone therapy, 15 of the 174 men with normal testosterone reported being on therapy, and 24 of the 34 men with high testosterone were on therapy.
Besides the positive effect on insulin levels, high testosterone was also associated with lower C-reactive protein -- a marker of inflammation -- levels (P<0.05).
There were no significant differences between the group in glycosylated hemoglobin A1c levels, in triglycerides, or in total cholesterol.
"Moderation in testosterone supplementation is important," said Helen Hilts, MD, of DiabeVita Medical Center in Scottsdale, Ariz.
She told MedPage Today that doctors should be seeking a balanced view, noting that testosterone supplementation does appear to improve some parameters of a man's metabolic profile.
Primary source: World Congress on Insulin Resistance, Diabetes and Cardiovascular Disease
Kapur S "Cardiometabolic risk factors and testosterone levels in men: Implications for testosterone supplementation" WCIR 2010; Abstract 65.