To clarify the probability of low serum testosterone level as a risk factor for metabolic syndrome (MS) in middle-aged men, we measured serum total testosterone (TT) and assessed several metabolic factors because the direct risk for MS has not been investigated fully in men.

This study comprised 1150 men aged ≥30 years. Physical and laboratory variables were assessed. Analyses were conducted to determine the association between serum TT level and incidence risk of MS and MS factors by a separate logistic regression model.

Mean (± standard deviation [SD]) serum TT level was 5.4 ± 1.7 ng/mL in the 1150 men, and only 92 men (8.0%) were classified as having MS by the Japanese criteria. In age-adjusted analyses, higher levels of serum TT were independently associated with a lower risk of MS (odds ratio, per SD decrement of TT, 2.3; 95% confidence interval [CI], 1.7-2.9). MS risk increased by lower quintile of TT: ORs were 15.1 (95% CI, 4.6-50.0) for first quintile, 8.8 (95% CI, 2.6-29.9) for second quintile, 5.8 (95% CI, 1.7-20.5) for third quintile, and 5.0 (95% CI, 1.4-17.9) for fourth quintile compared with highest quintile of TT. Age-adjusted ORs for the incidence of dichotomous components of MS per SD decrement of TT were 1.8 (95% CI, 1.5-2.3) for waist circumference, 1.6 (95% CI, 1.1-2.2) for dyslipidemia, and 1.5 (95% CI, 1.2-1.8) for hypertension.

We found that higher probability of MS was associated with lower levels of serum TT level in relatively healthy middle-aged Japanese men.