Relationship between mixed exposure to heavy metals and seminal fructose in men of childbearing age

Background The human body is usually exposed to a variety of heavy metals at the same time, and different types and concentrations of heavy metals may have complex interactions during their absorption and metabolism in the human body. Seminal fructose is an important energy source for sperm movement. A large number of studies have shown that metal exposure may impair semen quality, and seminal fructose is an important factor affecting male reproduction, so it is necessary to investigate the relationship between mixed heavy metal exposure and seminal fructose to explore the mechanism of semen quality damage caused by metal exposure.

Objective To understand the status of common heavy metal exposure in men of childbearing age in Puyang City, Henan Province, and to study the relationship between mixed exposure to heavy metals and seminal fructose, as well as potential interactions among heavy metals.

Methods Volunteers were recruited from the Puyang Maternal and Child Health Hospital Reproductive Center for a cross-sectional survey on general demographic characteristics, smoking, alcohol consumption, and other information. Semen samples were collected to detect 12 metals such as vanadium (V), manganese (Mn), cobalt (Co), nickel (Ni), zinc (Zn), selenium (Se), silver (Ag), cadmium (Cd), barium (Ba), thallium (Tl), iron (Fe), and lead (Pb) in seminal plasma and seminal fructose. After correcting for selected confounding factors, a Bayesian kernel machine regression (BKMR) model was used to evaluate the impact of seminal plasma heavy metal mixed exposure and its interactions on seminal fructose.

Results A total of 825 adult males were enrolled. The concentrations in M (P₂₅, P₇₅) of V, Mn, Co, Ni, Zn, Se, Ag, Cd, Ba, Tl, Fe, and Pb in seminal plasma were 0.39 (0.28, 0.54), 12.31 (8.92, 17.52), 0.26 (0.18, 0.38), 5.15 (3.32, 8.64), 182159.80 (121847.80, 199144.50), 13.61 (10.55, 17.68), 0.03 (0.02, 0.04), 0.34 (0.27, 0.46), 8.64 (5.94, 13.43), 0.06 (0.05, 0.08), 168.74 (114.17, 259.45), and 1.69 (1.15, 2.36) μg·L⁻¹ respectively. The Spearman correlation results indicated that there was a negative correlation between V, Mn, Co, Zn, Se, Ba, Tl, or Fe in seminal plasma and seminal fructose (P<0.05), and the values of r (95%CI) were −0.044 (−0.087, −0.001), −0.129 (−0.171, −0.087), −0.055 (−0.099, −0.012), −0.099 (−0.143, −0.056), −0.053 (−0.097, −0.010), −0.068 (−0.111, −0.025), −0.095 (−0.138, −0.052), and −0.082 (−0.125, −0.039), respectively. The results of multiple linear regression indicated that there was a negative correlation between the exposure level of Cd, Mn, Zn, Ag, Ba, Tl, or Fe in seminal plasma and seminal fructose (P<0.05), the values of associated β (95%CI) were −0.551 (−0.956, −0.147), −0.315 (−0.419, −0.212), −0.187 (−0.272, −0.103), −0.161 (−0.301, −0.021), −0.188 (−0.314, −0.062), −1.159 (−2.170, −0.147), and −0.153 (−0.230, −0.076), respectively. The BKMR model analysis showed that seminal fructose level decreased with the increase of plasma metal mixed exposure concentration. Compared with all metal exposure at P₅₀, the seminal fructose level decreased by 0.2374 units when all metal exposure was at P₇₅. Seminal plasma Zn posterior inclusion probabilities (PIPs)=1.0000 had the strongest effect on seminal fructose, followed by Mn (PIPs=0.5872), Se (PIPs=0.5656), and Ba (PIPs=0.5398). The univariate exposure-response curve showed a negative approximate linear correlations between Ba or Mn and seminal fructose, a positive linear correlation between Se and seminal fructose, and an approximate inverted U-shaped association between Zn and seminal fructose. No significant interaction between studied metals was found.

Conclusion  Mixed metal exposure may lead to decrease of seminal fructose, in which Zn, Mn, Se, and Ba may play an important role. Mn and Zn exposure may reduce the level of seminal fructose, Se may increase the level of seminal fructose, and there may be a threshold effect between Zn exposure and seminal fructose level. No interaction between different metals on seminal fructose is found.