Study question: What is the relationship between body size, physical activity and semen parameters among male partners of couples attempting to become pregnant?
Summary answer: Overweight and obesity are associated with a higher prevalence of low ejaculate volume, sperm concentration and total sperm count.
What is known already: Higher BMI is associated with impaired semen parameters, while increasing waist circumference (WC) is also associated with impaired semen parameters in infertile men.
Study design, size, duration: Data from the Longitudinal Investigation of Fertility and the Environment (LIFE) Study were utilized. The LIFE study is a population-based prospective cohort of 501 couples attempting to conceive in two geographic areas (Texas and Michigan, USA) recruited in 2005-2009. Couples were recruited from four counties in Michigan and 12 counties in Texas to ensure a range of environmental exposures and lifestyle characteristics. In person interviews were conducted to ascertain demographic, health and reproductive histories followed by anthropometric assessment.
Participants/materials, setting, methods: We categorized BMI (kg/m(2)) as <25.0 (underweight and normal), 25.0-29.9 (overweight) 30.0-34.9 (obese, class I) and ≥35 (obese, class II) for analysis. Data were available for analysis in 468 men (93% participation), with a mean ± SD age of 31.8 ± 4.8 years, BMI of 29.8 ± 5.6 kg/m(2) and WC of 100.8 ± 14.2 cm. The majority of the cohort (82%) was overweight or obese with 58% reporting physical activity <1 time/week. The median sperm concentration for the men in the cohort was 60.2 M/ml with 8.6% having oligospermia (<15 M/ml).
Main results and the role of chance: When examining semen parameters, ejaculate volume showed a linear decline with increasing BMI and WC (P < 0.01). Similarly, the total sperm count showed a negative linear association with WC (P < 0.01). No significant relationship was seen between body size (i.e. BMI or WC) and semen concentration, motility, vitality, morphology or DNA fragmentation index. The percentage of men with abnormal volume, concentration and total sperm increased with increasing body size (P < 0.05). No relationship between physical activity and semen parameters was identified.
Limitations, reasons for caution: Our cohort was largely overweight and sedentary, which may result in limited external validity, i.e. generalizability. The lack of physical activity did preclude examination of exercise more frequently than once per week, thus our ability to examine more active individuals is limited.
Wider implications of the findings: Body size (as measured by BMI or WC) is negatively associated with semen parameters with little influence of physical activity. Our findings are the first showing a relationship between WC and semen parameters in a sample of men without known infertility. Given the worldwide obesity epidemic, further study of the role of weight loss to improve semen parameters is warranted.
Study funding/competing interest(s): Supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (Contracts #N01-HD-3-3355, N01-HD-3-3356 and N01-HD-3-3358). There are no competing interests.
Keywords: fertility; male infertility; obesity; oligospermia; overweight.