Life Extension Magazine July 2007
Sex differences of endogenous sex hormones and risk of type 2 diabetes: a systematic review and meta-analysis.
CONTEXT: Inconsistent data suggest that endogenous sex hormones may have a role in sex-dependent etiologies of type 2 diabetes, such that hyperandrogenism may increase risk in women while decreasing risk in men. OBJECTIVE: To systematically assess studies evaluating the association of plasma levels of testosterone, sex hormone-binding globulin (SHBG), and estradiol with risk of type 2 diabetes. DATA SOURCES: Systematic search of EMBASE and MEDLINE (1966-June 2005) for English-language articles using the keywords diabetes, testosterone, sex-hormone-binding-globulin, and estradiol; references of retrieved articles; and direct author contact. STUDY SELECTION: From 80 retrieved articles, 43 prospective and cross-sectional studies were identified, comprising 6,974 women and 6,427 men and presenting relative risks (RRs) or hormone levels for cases and controls. DATA EXTRACTION: Information on study design, participant characteristics, hormone levels, and risk estimates were independently extracted by 2 investigators using a standardized protocol. DATA SYNTHESIS: Results were pooled using random effects and meta-regressions. Cross-sectional studies indicated that testosterone level was significantly lower in men with type 2 diabetes (mean difference, -76.6 ng/dL; 95% confidence interval [CI], -99.4 to -53.6) and higher in women with type 2 diabetes compared with controls (mean difference, 6.1 ng/dL; 95% CI, 2.3 to 10.1) (P<.001 for sex difference). Similarly, prospective studies showed that men with higher testosterone levels (range, 449.6-605.2 ng/dL) had a 42% lower risk of type 2 diabetes (RR, 0.58; 95% CI, 0.39 to 0.87), while there was suggestion that testosterone increased risk in women (P = .06 for sex difference). Cross-sectional and prospective studies both found that SHBG was more protective in women than in men (P< or =.01 for sex difference for both), with prospective studies indicating that women with higher SHBG levels (>60 vs < or =60 nmol/L) had an 80% lower risk of type 2 diabetes (RR, 0.20; 95% CI, 0.12 to 0.30), while men with higher SHBG levels (>28.3 vs < or =28.3 nmol/L) had a 52% lower risk (RR, 0.48; 95% CI, 0.33 to 0.69). Estradiol levels were elevated among men and postmenopausal women with diabetes compared with controls (P = .007). CONCLUSIONS: This systematic review indicates that endogenous sex hormones may differentially modulate glycemic status and risk of type 2 diabetes in men and women. High testosterone levels are associated with higher risk of type 2 diabetes in women but with lower risk in men; the inverse association of SHBG with risk was stronger in women than in men.
JAMA. 2006 Mar 15;295(11):1288-99
The pituitary-gonadal axis and health in elderly men: a study of men born in 1913.
The results of recent studies suggest that a relative hypogonadism in men is associated with several established risk factors for prevalent diseases. Therefore, we determined total and free testosterone, luteinizing hormone (LH), and sex-hormone binding globulin (SHBG) in a cohort of randomly selected men (n = 659) at 67 years of age. These data were analyzed cross-sectionally in relation to blood glucose and serum insulin, which were measured while fasting and after an oral glucose tolerance test, in addition to plasma lipids and blood pressure. The data were also analyzed in relation to impaired glucose tolerance (IGT) and diabetes, which were discovered at examination or earlier diagnosis. Risk factors for the development of diabetes up to 80 years of age were analyzed with univariate and multivariate statistics. Total and free testosterone and SHBG concentrations correlated negatively with glucose and insulin values; total testosterone and SHBG, with triglycerides; and SHBG, with blood pressure (from P < 0.05 to P < 0.01). Men with IGT or newly diagnosed diabetes had higher BMI values (26.2 +/- 0.31 and 27.0 +/- 0.59 [mean +/- SE], respectively) and waist circumference (99.0 +/- 1.03 and 100.5 +/- 1.57) than nondiabetic men (BMI, 25.1 +/- 0.14; waist circumference, 95.4 +/- 0.47; P < 0.05), indicating abdominal obesity. Such men and men with previously diagnosed diabetes had, in general, lower total and free testosterone and SHBG levels, while those for LH were not different. In multivariate analyses that included BMI, waist-to-hip ratio, total and free testosterone, and SHBG, the remaining independent predictors for the development of diabetes were low total testosterone (P = 0.015) and, on the borderline, low SHBG (P = 0.053). In relation to nondiabetic men, the risk ratio for mortality, myocardial infarction, and stroke increased gradually and significantly from 1.18 to 1.68, from 1.51 to 1.78, and from 1.72 to 2.46 in men with IGT, newly diagnosed diabetes, and previously known diabetes, respectively. It was concluded that low testosterone and SHBG concentrations in elderly men are associated with established risk factors for diabetes and in established diabetes. Moreover, low testosterone levels independently predict the risk of developing diabetes. In different degrees of expression, the diabetic state predicts strongly (and gradually mortality from) myocardial infarction and stroke. It has been suggested that a relative hypogonadism might be a primary event, because other studies have shown that testosterone deficiency is followed by insulin resistance, which is ameliorated by testosterone substitution. The data suggest that the relative hypogonadism involved might be of both central and peripheral origin.
Diabetes. 1996 Nov;45(11):1605-9
Association of obesity and insulin resistance with serum testosterone, sex hormone binding globulin and estradiol in older males.
There is an increased accumulation of fat tissue with subsequent increase of insulin level, insulin resistance and decrease of testosterone level in aging males. AIM OF THE STUDY: Assessment of the relations between obesity, insulin resistance and levels of sex hormones. MATERIAL AND METHODS: Indices of obesity (BMI, WHR, waist circumference), insulin level, insulin resistance (HOMA-IR) and levels of sex hormones (total testosterone, free testosterone, free testosterone index, sex hormone-binding globulin--SHBG, estradiol) were measured in 107 males at the mean age of 60.1 +/- 7 years. RESULTS: Obesity among aging males is associated with insulin resistance and hyperinsulinism. All above factors correlate with decreased serum levels of testosterone and sex hormone binding globulin as well as increased ratio estradiol/testosterone ratio. CONCLUSION: Our data suggest a role of decreased levels of testosterone and SHBG in pathogenesis of visceral obesity and metabolic syndrome in older males.
Pol Merkur Lekarski. 2005 Nov;19(113):634-7
Testosterone replacement therapy improves insulin resistance, glycaemic control, visceral adiposity and hypercholesterolaemia in hypogonadal men with type 2 diabetes.
OBJECTIVE: Low levels of testosterone in men have been shown to be associated with type 2 diabetes, visceral adiposity, dyslipidaemia and metabolic syndrome. We investigated the effect of testosterone treatment on insulin resistance and glycaemic control in hypogonadal men with type 2 diabetes. DESIGN: This was a double-blind placebo-controlled crossover study in 24 hypogonadal men (10 treated with insulin) over the age of 30 years with type 2 diabetes. METHODS: Patients were treated with i.m. testosterone 200 mg every 2 weeks or placebo for 3 months in random order, followed by a washout period of 1 month before the alternate treatment phase. The primary outcomes were changes in fasting insulin sensitivity (as measured by homeostatic model index (HOMA) in those not on insulin), fasting blood glucose and glycated haemoglobin. The secondary outcomes were changes in body composition, fasting lipids and blood pressure. Statistical analysis was performed on the delta values, with the treatment effect of placebo compared against the treatment effect of testosterone. RESULTS: Testosterone therapy reduced the HOMA index (-1.73 +/- 0.67, P = 0.02, n = 14), indicating an improved fasting insulin sensitivity. Glycated haemoglobin was also reduced (-0.37 +/- 0.17%, P = 0.03), as was the fasting blood glucose (-1.58 +/- 0.68 mmol/l, P = 0.03). Testosterone treatment resulted in a reduction in visceral adiposity as assessed by waist circumference (-1.63 +/- 0.71 cm, P = 0.03) and waist/hip ratio (-0.03 +/- 0.01, P = 0.01). Total cholesterol decreased with testosterone therapy (-0.4 +/- 0.17 mmol/l, P = 0.03) but no effect on blood pressure was observed. CONCLUSIONS: Testosterone replacement therapy reduces insulin resistance and improves glycaemic control in hypogonadal men with type 2 diabetes. Improvements in glycaemic control, insulin resistance, cholesterol and visceral adiposity together represent an overall reduction in cardiovascular risk.
Eur J Endocrinol. 2006 Jun;154(6):899-906
Prevalence of prostate cancer among hypogonadal men with prostate-specific antigen levels of 4.0 ng/mL or less.
OBJECTIVES: To determine the prevalence of prostate cancer in hypogonadal men with a prostate-specific antigen (PSA) level of 4.0 ng/mL or less. METHODS: A total of 345 consecutive hypogonadal men with a PSA level of 4.0 ng/mL or less underwent evaluation with digital rectal examination and prostate biopsy before initiating a program of testosterone replacement therapy. All men had low serum levels of total or free testosterone, defined as less than 300 and 1.5 ng/dL, respectively. RESULTS: Cancer was identified in 15.1%. The cancer detection rate was 5.6%, 17.5%, 26.4%, and 36.4% for a PSA level of 1.0 or less, 1.1 to 2.0, 2.1 to 3.0, and 3.1 to 4.0 ng/mL, respectively (P < 0.05). Cancer was detected in 26 (30.2%) of 86 men with a PSA level of 2.0 to 4.0 ng/mL. Cancer was detected in 21% of men with a testosterone level of 250 ng/dL or less compared with 12% of men with a testosterone level greater than 250 ng/dL (P = 0.04). Men with free testosterone levels of 1.0 ng/dL or less had a cancer rate of 20% compared with 12% for men with greater values (P = 0.04). The odds ratio of cancer detection for men in the lowest tertile compared with the highest tertile was 2.15 (95% confidence interval 1.01 to 4.55) for total testosterone and 2.26 (95% confidence interval 1.07 to 4.78) for free testosterone. CONCLUSIONS: Prostate cancer was present in more than 1 of 7 hypogonadal men with PSA of 4.0 ng/mL or less. An increased risk of prostate cancer was associated with more severe reductions in testosterone.
Urology. 2006 Dec;68(6):1263-7
Different mechanisms in testosterone action on glycogen metabolism in rat perineal and skeletal muscles.
Testosterone affects glycogen levels in perineal and skeletal muscles by two distinct mechanisms. Both of them show similar sensitivity to androgens (0.1 mg/rat/day of testosterone being effective) and to antiandrogen administration. However, they differ because of the pattern of glycogen increase (early after the androgen injection in the perineal muscles; slowly and with a linear function of time in the skeletal muscles), and because of the different sensitivities to adrenolectomy, diabetes and hypophysectomy. Also, the biochemical changes induced by testosterone in muscles differ. The rate of sugar uptake and phosphorylation is increased in the perineal muscle only; the rate of glucose incorporation into glycogen is increased in the perineal but depressed in the skeletal muscles. Therefore, in the former case glycogen accumulation depends mainly on increased synthesis; in the latter, it is probably the result of a glycogen sparing effect.
Endocrinology. 1975 Jan;96(1):77-84