Background: Aging is associated with variations in hypothalamic-pituitary-gonadal (HPG) axis hormones. However, it is not clear how aging changes these hormones. This study examined the natural alterations in the HPG axis in aging men and women in China. Methods: Data were obtained from our cross-sectional study (SPECT-China) in 16 areas of three provinces in East China between February and June 2014. There were 6,825 subjects selected, including 2,908 men and 3,917 women aged 25-93 years who had no diseases affecting HPG hormones and did not take exogenous supplements. Total testosterone (TT), estradiol (E2), free testosterone, sex hormone-binding globulin (SHBG), follicle-stimulat-ing hormone (FSH) and luteinizing hormone (LH) were measured. Results: In men, the ranges of the 10-90th percentiles for each hormone were as follows: TT, 9.9-23.4 nmol/l; SHBG, 20.6-79.54 nmol/l; E2, 34.84-187 pmol/l. TT values were higher in men aged 25-30 years than in those aged 31-35 years and began to increase progressively at the age of 41-50 years until men reached their eighties. The unadjusted annual age trend ((3) was 0.079 nmol/l/year (p < 0.001). A linear regression analysis, after full adjustment for demographic variables, metabolic factors, other hormones, lifestyle and co-morbidities, showed that higher TT levels were still associated with aging (p < 0.05). However, the ratio of TT to LH decreased with age ((3 = 0.272/year, p < 0.001). E2 and SHBG increased with age ((3=1.774 pmol/l/year and 1.118 nmol/l/year, respectively, p < 0.001). In women, the 10-90th percentile range of E2 was 32.79-565.8 pmol/I. E2 began to decrease at the age of 46-50 years, declined sharply at the age of 51-55 years ((3=5.73 pmol/l/year, p < 0.001) and then stabilized at a low concentration after the age of 55 years. The 10-90th percentile ranges of LH and FSH in men were 2.4-9.2 and 3.4-15.5 IU/I, and in women they were 3-36.6 and 4-89.28 IU/I, respectively. FSH increased by 7.11% per annum in men and by 12.76% per annum in women, but LH increased by only approximately 4.00% per annum in both sexes. Conclusions: The influence of aging on the HPG axis is sex dependent. The pattern of age-related TT was different in Chinese Han men when compared with previous studies in Western populations. TT values increased in aging men, so it is not suitable to estimate the life quality of older Chinese men just based on TT. (C) 2016 S. Karger AG, Basel