Dynamic alteration of serum testosterone with aging: a cross-sectional study from Shanghai, China

Level of the testosterone in a man's life span is very important. Studies on the serum testosterone concentrations in different age groups of healthy men were controversial. The aim of this study was to investigate dynamic changes of serum reproductive hormones with aging in healthy Chinese male and to compare its correlation with age.

Total of 1,093 healthy Chinese men from Shanghai aged from 20 to 87  years old was enrolled in the study. Concentrations of serum total testosterone (T), luteinizing hormone (LH) and sex hormone binding globulin (SHBG) were quantified by EIA. Testosterone secretion index (TSI) and free testosterone index (FTI) were then calculated. Data were analyzed by SPSS program. Non-parametric tests and univariate linear regression analyses were used.

The 1,039 male participants were grouped into 12 groups by 5-year apart for each group. Significant differences in T, LH, SHBG, FTI and TSI were found between the 12 different age groups. Average of serum total T was 15.36 ± 4.86 nmol/L; LH was 4.76 ± 2.76 IU/L, SHBG was 32.61 ± 17.24 nmol/L. Compared to age 20 ~ 24 group, serum T level of age 35 ~ 39, 40 ~ 44, 45 ~ 49, 50 ~ 54, and 55 ~ 59 was significantly decreased (p < 0.05). Intriguingly, however, serum T level of age 60 or older did not significantly reduced compared to the age of 20 ~ 24 group. Serum LH and SHBG were positively correlated with aging (p <0.01), while TSI and FTI were negatively correlated with aging (p <0.01). In addition, BMI was negatively and significantly correlated with levels of T (r = -0.585, p < 0.001), LH (r = -0.090, p < 0.001), SHBG (r = - 1.817, p < 0.001), and TSI (r = - 0.104, p < 0.001), but positively and significantly correlated with FTI level (r = 0.011, p < 0.001).

Serum total testosterone fluctuated with aging in adult men, and FTI and TSI decreased gradually with aging. While age was not significantly correlated with T level, BMI was significantly and negatively correlated with T level, suggesting body weight may affect testosterone level.