Infertility affects approximately 15% of couples worldwide and represents a growing public health concern, with male factors contributing to nearly half of all cases [1] [2] . While genetic and lifestyle factors play an important role, increasing attention has been directed toward environmental exposures—particularly endocrine-disrupting chemicals (EDCs) [3] —which can adversely affect the hypothalamic–pituitary–gonadal (HPG) axis and impair spermatogenesis [4] - [6] .

Among EDCs, heavy metals such as cadmium (Cd), lead (Pb), arsenic (As), and chromium (Cr) are particularly concerning due to their widespread presence and cumulative toxicity [7] . These metals are released into the environment through industrial emissions, vehicular exhaust, and improper waste disposal practices [7] [8] . Once absorbed, they accumulate in reproductive tissues and exert toxic effects by disrupting hormone synthesis and testicular function [6] [9] .

Heavy metals contribute to male infertility primarily by promoting the excessive production of reactive oxygen species (ROS), leading to oxidative stress and cellular damage [10] . ROS—including superoxide anions, hydrogen peroxide, and hydroxyl radicals—damage lipids, proteins, and nucleic acids, thereby compromising sperm function [11] [12] . While physiological ROS levels are essential for processes such as sperm capacitation and the acrosome reaction, elevated ROS levels disrupt mitochondrial membrane potential, reduce motility, and trigger apoptosis in germ cells [12] - [14] .

The antioxidant defense system—comprising enzymatic components (e.g., superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx]) and non-enzymatic molecules (e.g., coenzyme Q10 [CoQ10], glutathione, vitamins C and E)—is vital for neutralizing oxidative stress [15] . However, heavy metals impair this defense system by inhibiting antioxidant enzyme activity and depleting intracellular antioxidant reserves [16] - [18] . This oxidative imbalance leads to impaired spermatogenesis, abnormal sperm morphology, and reduced motility—all key parameters associated with male infertility [19] - [21] . Numerous epidemiological and experimental studies have confirmed that exposure to heavy metals significantly compromises semen quality and disrupts reproductive hormone levels [22] - [24] .

Given the oxidative pathogenesis of metal-induced infertility, antioxidant supplementation has emerged as a promising therapeutic strategy [21] [25] . CoQ10, zinc, and D-aspartic acid are among the most extensively studied compounds in this context. CoQ10 serves as both a mitochondrial electron carrier and a lipid-soluble antioxidant, enhancing sperm motility and ATP production [26] [27] . Zinc, a cofactor for multiple antioxidant enzymes, stabilizes sperm chromatin and supports testosterone biosynthesis [28] [29] . D-aspartic acid stimulates the release of gonadotropins and testosterone by acting on the hypothalamus and Leydig cells [23] [30] .

Despite evidence supporting the individual benefits of these compounds [8] , few studies have evaluated their combined efficacy, especially in this specific case of men exposed to occupational heavy metals. Therefore, the present study aims to evaluate the therapeutic potential of a combined antioxidant supplementation regimen—including CoQ10, zinc, and D-aspartic acid—in improving semen quality among men with documented environmental heavy metal exposure.

This randomized controlled study investigated the impact of a three-month antioxidant supplementation—CoQ10 (ubiquinol), zinc, and D aspartic acid (D Asp)—on semen quality. The primary finding was a statistically significant improvement in progressive sperm motility in the supplemented group compared to controls, whereas no significant differences were observed in the other parameters, such as semen volume, sperm concentration, total sperm count, morphology, and leukocyte presence. These findings are consistent with previous clinical trials and in vitro studies [8] , which consistently identify motility as the most responsive semen parameter to antioxidant supplementation [32] .

CoQ10 and zinc are essential for mitochondrial function and redox balance, directly supporting sperm motility by enhancing ATP production and reducing oxidative damage [12] . D-Asp plays a role in stimulating the hypothalamic–pituitary–gonadal axis and supporting spermatogenesis, contributing to functional sperm output [33] . A recent randomized, double-blind, placebo-controlled trial by GamalEl Din et al. (2025) found a significant increase in progressive motility and testosterone levels in men receiving a similar combination of 2660 mg D-Asp, 200 mg ubiquinol, and 10 mg zinc over three months [32] . Complementary observational data from Gvozdjáková et al., 2015, using an ubiquinol-containing multi-ingredient regimen (without D-Asp or zinc), reported improvements in semen quality and oxidative-stress biomarkers (higher seminal CoQ10 and α-tocopherol, lower oxidative markers), although the absence of a control arm and the different composition limit direct comparability [34] . These results mirror our findings and support the biological plausibility of the observed effects.

Additional evidence from in vitro studies confirms that this antioxidant combination helps preserve sperm motility, reduces lipid peroxidation, and mitigates DNA fragmentation, even in cryopreserved or incubated samples [35] [36] . Supplementation of sperm culture media with zinc, d-aspartate, and coenzyme Q10 could protect sperm from oxidative stress damage during in vitro handling in assisted reproductive technologies [8] . Meta-analyses and systematic reviews further reinforce the efficacy of CoQ10 in improving motility, though effects on concentration and morphology remain inconsistent across studies.

Despite a trend toward improved sperm count and concentration in our supplemented group, these differences did not reach statistical significance—likely due to the small sample size and relatively short intervention duration. Moreover, our study did not assess clinical outcomes such as natural conception or live birth, limiting broader conclusions regarding fertility potential.

The growing body of evidence supports the targeted use of antioxidant supplementation, particularly in cases of idiopathic male infertility or isolated asthenozoospermia [37] . Future studies should include larger sample sizes, longer follow-up periods, dose–response evaluations, and clinical endpoints such as time to pregnancy or assisted reproductive success rates. Additionally, combining supplementation with lifestyle modifications may further enhance outcomes.

Our findings support the role of coenzyme Q10, zinc, and D-aspartic acid supplementation in improving progressive sperm motility—an essential determinant of male fertility—in men occupationally exposed to heavy metals. Although other semen parameters showed variable and non-significant changes, the direction of effects and coherence with prior in vivo and clinical evidence point to a biologically plausible, motility-focused benefit. These results should be interpreted with caution: exposure was inferred from occupational category rather than quantified with blood or seminal metal levels, preventing an exposure–response analysis and potentially introducing non-differential misclassification; the study was small, single-center, and of short duration with a single-blind design; and we did not assess clinical fertility endpoints or mechanistic biomarkers such as redox status or sperm DNA damage. Within these constraints, the supplement was well tolerated, and the improvement in progressive motility appears clinically meaningful. Future research should confirm these findings in larger, double-blind, placebo-controlled cohorts, incorporate biomarker-based exposure assessment and mechanistic readouts, extend follow-up to fertility outcomes, and explore dose–response effects and stratification by baseline motility and exposure intensity.

A.P. conception and design, F.S. and S.N. data collection and interpretation, F.S. wrote the manuscript. A.P. provided suggestions and revised the manuscript for final submission. All authors have read and agreed to the published version of the manuscript.