Background: In animals, some phthalates impair male reproductive development and function. Epidemiological studies have reported inconsistent evidence of associations between phthalates and markers of human testicular function.
Objectives: We aimed to provide estimates of the effects of phthalate exposure on reproductive hormone levels and semen quality in healthy men.
Methods: A total of 881 men gave urine, serum, and semen samples. Serum levels of testosterone, estradiol (E2), sex hormone-binding globulin (SHBG), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and inhibin-B; semen quality; and urinary concentrations of 14 phthalate metabolites, including metabolites of di(2-ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DiNP), were assessed. The proportions of DEHP and DiNP excreted as their respective primary metabolites [mono(2-ethylhexyl) phthalate (MEHP) and mono-isononyl phthalate (MiNP)] were calculated and expressed as percentages (%MEHP and %MiNP, respectively).
Results: The free androgen index was 15% lower [95% confidence interval (CI): -23, -8%] for men in the highest %MiNP quartile compared to the lowest quartile (p < 0.001) after adjusting for confounders, and 9% lower (95% CI: -16, -1%) in the highest %MEHP quartile (p = 0.02). %MEHP and %MiNP were negatively associated with the ratio of testosterone/LH and testosterone/FSH. %MEHP was negatively associated with total testosterone, free testosterone, and ratio of testosterone/E(2). %MiNP was positively associated with SHBG. There was little evidence of associations between urinary phthalate metabolites or sums of phthalates with reproductive hormones or semen quality.
Conclusion: Our data suggest that both testosterone production and pituitary-hypothalamic feedback may be compromised in individuals excreting a high proportion of primary metabolites of long-chained phthalates relative to the proportion of secondary metabolites.