The relationship between body mass index (BMI) and reproductive hormone levels and sperm parameters in relatively healthy individuals

Infertility affects approximately 13% to 15% of couples worldwide, with 1 in 5 couples unable to achieve pregnancy within the first year of trying. Obesity is recognized as a significant modifier of reproductive hormones, with evidence suggesting its role in declining sperm parameters, given the rising prevalence of obesity globally. This study aimed to evaluate the relationship between body mass index (BMI), sperm parameters, and reproductive hormone levels in relatively healthy individuals. Participants who met the inclusion criteria were categorized into four groups based on fertility status (normozoospermic fertile men and infertile patients) and BMI classification: normal weight (BMI: 18.5–24.9 kg/m²), overweight (BMI: 25–29.9 kg/m²), and obese (BMI ≥ 30 kg/m²). Semen parameters, reproductive hormone levels, and thyroid-stimulating hormone (TSH) levels were retrospectively compared across groups. There were no significant differences in age or height between the groups. However, sperm count, semen volume, and BMI varied significantly across the groups. The BMI values for non-obese infertile, obese infertile, non-obese fertile, and obese infertile men were 42.3 ± 5.7, 89.4 ± 12.7, 51.0 ± 9.8, and 86.9 ± 10.9, respectively (p < 0.001). Significant differences were also observed between groups in serum levels of follicle-stimulating hormone, luteinizing hormone, TSH, prolactin, semen volume, sperm concentration, and total sperm count (p < 0.001). These findings suggest that male obesity may influence semen characteristics and alter reproductive hormone levels.