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Aim: To examine whether reproductive hormones play a role in the association between body mass index (BMI) and semen quality. Methods: Semen quality and testosterone (T), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and estradiol (E2) were evaluated in 990 fertile males with age 38.9 ± 9.7 (mean ± SD) years recruited from the Chinese general population in 2001 and 2002. Results: Semen quality was reduced among underweight (BMI < 18.5) compared with normal (BMI 18.5–24.9) and overweight (BMI 25.0–29.9), but the associations were independent of reproductive hormones. After adjustment for the potential confounders, underweight men had reductions in sperm concentration (22.4 × 10 6 /mL), total sperm count (52.9 × 10 6 ) and percentage of normal sperm forms (6.9%) compared with men with normal BMI. Being underweight may be a risk factor for low sperm concentration (OR: 4.68, 95% confidence intervals [CI]: 2.01–10.91). Otherwise, being overweight may be a protected factor for low sperm concentration (OR: 0.25; 95% CI: 0.08–0.83) and low total sperm count (OR: 0.37, 95% CI: 0.15–0.87). Conclusion: Low BMI was associated with reduced semen quality. The associations between BMI and semen quality were found statistically significant even after adjustment for reproductive hormones. Reproductive hormones cannot explain the association between BMI and semen quality. (Asian J Androl 2007 Nov; 9: 827–834)

To explore the association between age and variables of semen in Chinese males with normal fertility.The population size under study would consist of 946 fertile male volunteers from 6 provinces of China, aged between 20 and 59. Semen quality was analyzed by hand on site and background information was obtained through structured questionnaire. Trend chi-square test and multiple linear regression methods were used and 95%CI were calculated to serve as reference value of semen variables of different age group.The normal percent of motility and living sperm declined significantly while the ascending of age, they were 55.7% and 97.3% in age30 group when compared to 21.9% and 90.3% in the age 50 - 59 group respectively. Under control of confounding factors as for center and abstinence time, all semen variables except semen volume were significantly different among the age groups. Sperm concentration, percentage of sperm motility and normal morphology sperm decreased significantly after age 40 while percentage of living sperm decreased after age 50 - 59 group. Sperm concentration among the 50 - 59 year-old group appeared to be lower than the 40 - year-old group.The influence of age must be taken into account when evaluating the quality of semen.