Review on the role of antioxidant supplementation against oxidative stress: a human and animal approach to male fertility

Male infertility is one important factor among the multifactorial causes of couple infertility, being oxidative stress one of the main related sources. Sperm is a specialized cell extremely susceptible to stress. To understand and mitigate this event, many studies have used different antioxidants, orally or in vitro supplementation, trying to improve sperm quality and function. Considering the extensive available literature regarding approaches and attempts to solve male fertility issues, the aim of this review is evaluating the effects of antioxidant supplementation on sperm, in both humans and experimental models with animals. This review selected original data from PubMed. The keywords used were: antioxidant, sperm, male fertility, antioxidant supplementation, male infertility; and the term "rodents" was added to the descriptors “antioxidant” and “male fertility”. Only studies published in indexed journals, in English, between 2015 and 2019 were included. This review involves i) human sperm and ii) rodent sperm. For the human approach, the search retrieved 496 articles and 80 were included, among which 28 studies were of in vitro antioxidant supplementation, 19 involved oral antioxidant supplementation and the remaining 33 concerned quantification of oxidants and antioxidants already present in the seminal samples. For the rodent approach, 152 articles were retrieved and 52 were included: 3 of varicocele, 11 of diabetes, 10 of therapeutic drugs, 3 of physical exercise, 10 of environmental exposure and 3 of heat stress. The remaining studies involved oxidative stress status in experimental models. Antioxidants use for reproductive purposes is increasing in an attempt to achieve better gametes and embryos. Vitamins C, B and E, selenium and zinc are the most commonly used antioxidants, with remarkable evidences in improving pathophysiological seminal conditions.