Human breast milk contamination with phthalates and alterations of endogenous reproductive hormones in infants three months of age

Abstract

Phthalates adversely affect the male reproductive system in animals. We investigated whether phthalate monoester contamination of human breast milk had any influence on the postnatal surge of reproductive hormones in newborn boys as a sign of testicular dysgenesis.

Design: We obtained biologic samples from a prospective Danish-Finnish cohort study on cryptorchidism from 1997 to 2001. We analyzed individual breast milk samples collected as additive aliquots 1-3 months postnatally (n = 130; 62 cryptorchid/68 healthy boys) for phthalate monoesters [mono-methyl phthalate (mMP), mono-ethyl phthalate (mEP), mono-n-butyl phthalate (mBP), mono-benzyl phthalate (mBzP), mono-2-ethylhexyl phthalate (mEHP), mono-isononyl phthalate (miNP)]. We analyzed serum samples (obtained in 74% of all boys) for gonadotropins, sex-hormone binding globulin (SHBG), testosterone, and inhibin B.

Results: All phthalate monoesters were found in breast milk with large variations [medians (minimum-maximum)]: mMP 0.10 (< 0.01-5.53 microg/L), mEP 0.95 (0.07-41.4 microg/L), mBP 9.6 (0.6-10,900 microg/L), mBzP 1.2 (0.2-26 microg/L), mEHP 11 (1.5-1,410 microg/L), miNP 95 (27-469 microg/L). Finnish breast milk had higher concentrations of mBP, mBzP, mEHP, and Danish breast milk had higher values for miNP (p = 0.0001-0.056). No association was found between phthalate monoester levels and cryptorchidism. However, mEP and mBP showed positive correlations with SHBG (r = 0.323, p = 0.002 and r = 0.272, p = 0.01, respectively); mMP, mEP, and mBP with LH:free testosterone ratio (r = 0.21-0.323, p = 0.002-0.044) and miNP with luteinizing hormone (r = 0.243, p = 0.019). mBP was negatively correlated with free testosterone (r = -0.22, p = 0.033). Other phthalate monoesters showed similar but nonsignificant tendencies.

Conclusions: Our data on reproductive hormone profiles and phthalate exposures in newborn boys are in accordance with rodent data and suggest that human Leydig cell development and function may also be vulnerable to perinatal exposure to some phthalates. Our findings are also in line with other recent human data showing incomplete virilization in infant boys exposed to phthalates prenatally.

Figure 1

Concentration of six phthalate monoesters (μg/L) in human breast milk samples from Denmark (n = 65) and Finland (n = 65), 1997–2001, collected between 1 and 3 months postnatally as additive aliquots. Data are given as percentile distribution. (A) mMP, (B) mEP, (C) mBP, (D) mBzP, (E) mEHP, (F) miNP.

Figure 2

Regression plots of mEP levels (μg/L) in human breast milk and serum hormonal levels in boys 3 months of age (n = 96). The x- and y-axes for mEP, free testosterone, SHBG, and LH:free testosterone ratio are logarithmic. The slopes (confidence interval) of the regression lines are (A) free testosterone, 0.86 (0.69–1.06); (B) LH:free testosterone ratio, 1.26 (0.99–1.60); and (C) SHBG 1.15 (1.03–1.28). Example of interpretation: A 10-fold increase in mEP, for example, from 1 to 10 μg/L, is associated with a 15% increase in SHBG from 140.5 to 161.3 nmol/L.