in men , testosterone concentrations decline gradually with age , unlike the dramatic fall in estrogen levels at the time of menopause in women .
testosterone deficiency is common in men with type 2 diabetes and it may contribute to not only impaired performance , mood , and libido , but also insulin resistance and metabolic abnormalities such as hypertension and dyslipidemia .
the endocrine society clinical practical guidelines indicate that men with type 2 diabetes have a high prevalence of low serum testosterone concentrations , and the guidelines recommend measuring serum testosterone concentrations .
furthermore , the inverse association between serum testosterone concentrations and plasma glucose concentrations has been observed in many studies .
however , serum testosterone concentrations in korean men with poorly controlled type 2 diabetes have never been studied . in this study
, we examined whether serum testosterone concentrations are low in korean men with poorly controlled type 2 diabetes compared with healthy men .
in this study , we enrolled 41 healthy men who underwent general health checks and 38 men with type 2 diabetes who were hospitalized at the cha bundang medical center , cha university , seongnam , korea .
the healthy men were matched to the diabetic men by age and body mass index ( bmi ) .
all participants were aged 40 years or above in the recruitment period , from april 2010 to october 2011 .
we excluded subjects who had type 1 diabetes , acute disease , known liver or kidney disease , history of stroke , angina , myocardial infarction , or cancer .
this study was approved by the cha university institutional review board , and informed consent was obtained from each study participant .
total testosterone was measured using chemiluminescent microparticle immunoassay with an architect i1000 immunology analyzer ( abbott laboratories , north chicago , il , usa ) .
sex hormone - binding globulin ( shbg ) levels were determined with a cobas 6000 analyzer ( roche , mannheim , germany ) .
free and bioavailable testosterone values were calculated from total testosterone , shbg , and serum albumin values based on mass action laws using vermeulen 's formula .
glycated hemoglobin ( hba1c ) , triglyceride , total and high density lipoprotein cholesterol , and glucose values were measured by standard methods .
testosterone deficiency was designated as individuals with a total testosterone level less than 3 ng / ml .
data for continuous variables are presented as meanssds and categorical factors are reported as percentages .
the participants ' characteristics were compared according to diabetes status using independent - sample t tests for continuous variables and chi - square tests for categorical variables .
in this study , we enrolled 41 healthy men who underwent general health checks and 38 men with type 2 diabetes who were hospitalized at the cha bundang medical center , cha university , seongnam , korea .
the healthy men were matched to the diabetic men by age and body mass index ( bmi ) .
all participants were aged 40 years or above in the recruitment period , from april 2010 to october 2011 .
we excluded subjects who had type 1 diabetes , acute disease , known liver or kidney disease , history of stroke , angina , myocardial infarction , or cancer .
this study was approved by the cha university institutional review board , and informed consent was obtained from each study participant .
total testosterone was measured using chemiluminescent microparticle immunoassay with an architect i1000 immunology analyzer ( abbott laboratories , north chicago , il , usa ) .
sex hormone - binding globulin ( shbg ) levels were determined with a cobas 6000 analyzer ( roche , mannheim , germany ) .
free and bioavailable testosterone values were calculated from total testosterone , shbg , and serum albumin values based on mass action laws using vermeulen 's formula .
glycated hemoglobin ( hba1c ) , triglyceride , total and high density lipoprotein cholesterol , and glucose values were measured by standard methods .
testosterone deficiency was designated as individuals with a total testosterone level less than 3 ng / ml .
data for continuous variables are presented as meanssds and categorical factors are reported as percentages .
the participants ' characteristics were compared according to diabetes status using independent - sample t tests for continuous variables and chi - square tests for categorical variables .
all statistical analyses were conducted using spss version 17.0 ( spss inc . , chicago , il , usa ) .
the mean age of men with type 2 diabetes was 55.8 years while that of healthy men was 51.9 years .
the average duration of diabetes was 10.8 years from the time of diagnosis ; the mean hba1c value was 10.8% .
there was no significant difference in age , bmi , waist circumference , systolic and diastolic blood pressure , total cholesterol , or shbg level between men with poorly controlled type 2 diabetes and healthy men .
however , men with poorly controlled type 2 diabetes had higher fasting blood glucose levels and lower serum albumin concentrations than the healthy men .
total testosterone concentrations were lower in men with poorly controlled type 2 diabetes than in healthy men after adjusting for age and bmi ( 3.830.32 ng / ml vs. 5.630.31 ng / ml , p<0.001 ) .
men with type 2 diabetes also showed lower calculated bioavailable testosterone concentrations than healthy men ( 1.580.12 ng / ml vs. 2.270.11 ng / ml , p<0.001 ) , but not calculated free testosterone concentrations .
the prevalence of testosterone deficiency was consistently higher in men with poorly controlled type 2 diabetes than in healthy men ( 31.6% vs. 2.4% , p<0.001 ) ( table 2 ) .
many studies have documented an association between low testosterone concentrations and type 2 diabetes in men .
the inverse association between serum testosterone concentrations and plasma glucose concentrations has also been well documented .
however , few studies have investigated serum testosterone concentrations in men with poorly controlled type 2 diabetes . in this study , we showed that total and bioavailable testosterone concentrations were lower in men with poorly controlled type 2 diabetes than in healthy men . in the blood of normal men , 44% of total testosterone
is bound to shbg , 2% is unbound , and 54% circulates bound to albumin and other proteins . because several studies have demonstrated that shbg levels are low in type 2 diabetes , low total testosterone concentrations might be a secondary consequence to the association between low shbg levels and type 2 diabetes . however , it is unclear whether low total testosterone concentrations are a consequence of low shbg levels in men with type 2 diabetes .
indeed , it is also clear that the relationship between low testosterone concentrations and type 2 diabetes is not solely due to shbg levels because many studies have shown that the inverse association between testosterone and insulin resistance is independent of shbg levels . in this study , men with poorly controlled type 2 diabetes had lower total testosterone concentrations than healthy men , although there is no difference in shbg levels .
therefore , men with poorly controlled type 2 diabetes should undergo further evaluation for symptoms and signs consistent with androgen deficiency . however , it is not clear why shbg is not different between men with poorly controlled type 2 diabetes and healthy men in this study .
many studies have demonstrated that low levels of shbg in men are consistently associated not only with type 2 diabetes , but also with visceral obesity , insulin resistance , and hyperinsulinemia . in this study , men with poorly controlled type 2 diabetes might have insulin deficiency rather than insulin resistance because the average duration of type 2 diabetes is more than 10 years , so shbg levels might not have been different between men with poorly controlled type 2 diabetes and healthy men .
unfortunately , we have no data about serum insulin and c - peptide levels , so we are not able to identify a relationship between shbg levels and insulin secretion or resistance .
several studies have documented that serum luteinizing hormone ( lh ) concentrations correlate positively with serum free testosterone concentrations ( hypogonadotrophic hypogonadism ) in men with type 2 diabetes .
in addition , mean lh levels and diurnal lh pulse amplitudes are significantly lower in obese subjects than in controls .
however , in this study , men with type 2 diabetes had normal lh concentrations .
this might be because the men with poorly controlled type 2 diabetes were not obese compared with the healthy men .
hyperglycemia itself might influence differences in serum testosterone concentrations between men with poorly controlled type 2 diabetes and healthy men . in this study ,
testosterone concentrations were found to be negatively correlated with fasting blood glucose and hba1c values ( data not shown ) , although the sample size is small .
furthermore , reduced testosterone concentrations in men with poorly controlled type 2 diabetes may be an effect of glycemia on the testicular microvasculature or leydig cell function .
first , no causal relationships among low serum testosterone concentrations and poorly controlled type 2 diabetes could be established due to the small sample size and cross - sectional nature of the study .
third , in this study , serum albumin levels were lower in men with type 2 diabetes than in healthy men .
this finding is consistent with previous studies showing that albumin levels might be significantly affected by poor glucose control .
we could not rule out the possibility that low serum albumin levels might have resulted in low testosterone concentrations in men with poorly controlled type 2 diabetes . finally , because we compared serum testosterone concentrations between men with poorly controlled type 2 diabetes and healthy men , we were not able to determine whether there was a significant association between glucose control and serum testosterone concentrations .
, this study shows that serum testosterone concentrations are lower in men with poorly controlled type 2 diabetes than in healthy men .
therefore , men with poorly controlled type 2 diabetes should undergo further assessment for hypogonadism .
 our aim was to examine whether serum testosterone concentrations are in fact low in hospitalized men with poorly controlled type 2 diabetes compared with healthy men . in this study , 79 men aged 40 years or older ( 41 healthy men and 38 men with type 2 diabetes ) were included . 
 total testosterone and sex hormone - binding globulin levels were measured . 
 the average duration of diagnosed diabetes was 10.8 years and the mean glycated hemoglobin value was 10.8% . 
 total testosterone concentrations were lower in men with type 2 diabetes than in healthy men , after adjusting for age and body mass index ( 3.830.32 ng / ml vs. 5.630.31 ng / ml , p<0.001 ) . in conclusion , this study shows that serum testosterone concentrations are lower in hospitalized men with poorly controlled type 2 diabetes than in healthy men . 
 therefore , men with poorly controlled type 2 diabetes should undergo further assessment for hypogonadism . 