Relationship between body mass index and infertility in healthy male Japanese workers: a pilot study.

Our aim was to evaluate the relationship between men's body mass index (BMI) and infertility and to examine the effects of factors related to metabolic syndrome such as hypertension, dyslipidaemia, and impaired glucose tolerance. Our sample comprised 74 healthy Japanese workers at a company who were married between 2003 and 2005. The outcome variable was whether a baby was born during the study period (median follow-up period, 20 months; range, 8-42 months). Data for BMI and other factors were obtained from the results of an annual health checkup in the year of each employee's marriage. Forty-seven men (64%) did not father a baby. Having a baby was significantly associated with a low BMI (21.4 versus 23.2 kg m(-2); P = 0.006). A Cox proportional hazard regression model was performed to assess the association of BMI with fathering a baby. Adjusting for age, systolic and diastolic blood pressure, low density lipoprotein cholesterol, triglycerides, and haemoglobin A(1C), higher BMI was significantly associated with not fathering a baby (hazard ratio, 0.80; 95% confidence interval, 0.67-0.95; P = 0012). High BMI in men was independently associated with an increased risk of not siring a child.