In clinical practice, doctors often recommend the use of vitamin E, multivitamins, coenzyme Q10 and Toluen for women of advanced age and for patients with reduced ovarian function or poor egg or embryo quality. Why is this? In this article, we will briefly introduce the reasons for this. 1. Aging and oxidative stress The ovaries are the first part of the female reproductive system to age. Egg quality declines significantly as women age, leading to an increased rate of aneuploidy in embryos developed from aging oocytes, an increased rate of miscarriage, and an increased incidence of birth defects in the offspring. Although the mechanism is not yet clear, numerous studies have shown that age-related decline in egg quality is associated with oxidative stress damage. Oxidative stress-induced oxidative damage to biomolecules plays an important role in the aging process. Oxidative stress (OS) is a pathological process in which the body produces too much reactive oxygen species (ROS) and/or the body’s antioxidant capacity decreases and ROS scavenging is insufficient, leading to an increase in ROS in the body and causing oxidative cellular damage. 2, reactive oxygen species (ROS) ROS is an important product of normal aerobic metabolism, and as a signaling molecule of redox reactions, affects cellular functions by regulating intracellular metabolites and signal transduction pathways. Under normal conditions, the production and clearance of ROS maintain a dynamic balance so that ROS are maintained at low levels necessary for cellular function. However, as the aging process progresses, the mechanisms that maintain intracellular homeostasis are gradually impaired, leading to excessive ROS production and/or impaired cellular antioxidant mechanisms, resulting in the accumulation of ROS. Large amounts of ROS act on intracellular lipids, proteins, peptides, nucleic acids and other biomolecules, leading to loss of cell membrane integrity, changes in protein structure and function, and nucleic acid damage; in turn, the accumulation of this oxidative damage can cause cellular senescence, further accelerating the production of ROS, forming a vicious cycle. 3, the effect of ROS on eggs and embryos There are two main sources of ROS in oocytes and embryos: one is from endogenous factors, such as the process of cellular whistling and apoptosis; the other is exogenous factors, such as obesity, malnutrition, smoking, alcohol consumption and environmental pollution can cause the accumulation of ROS and cause oxidative stress damage. The large amount of ROS puts the mitochondria in a high oxidative stress environment and increases the rate of mitochondrial DNA mutations, which in turn leads to structural changes in the oocyte. Oxidative stress damage in oocytes can also lead to abnormal meiosis or arrest of oocyte meiosis, induce premature cell regulation, and affect oocyte maturation. Oxidative stress damage to embryos can lead to a decrease in the number of embryonic cells and an increase in the rate of fragmentation, causing embryonic development to stall or even apoptosis. 4.Antioxidants There are two types of antioxidants in human body, namely enzymatic antioxidants and non-enzymatic antioxidants, which constitute the internal and external antioxidant stress protection system of human body, and inhibit the oxidative stress response in the body by synergistically scavenging the excess ROS. Enzymatic antioxidants include catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). Enzymatic antioxidants exert antioxidant effects by neutralizing excess ROS and effectively eliminating oxygen radicals produced by cells during metabolism. Non-enzymatic antioxidants include vitamin C, vitamin E, L-carnitine, pyruvate, taurine, cysteamine and glutathione. Human follicular fluid and oviductal fluid contain large amounts of non-enzymatic antioxidants, which can protect oocytes from ROS-induced damage. 5. Application of antioxidants Oxidative stress damage in oocytes and embryos is associated with a decrease in the antioxidant capacity of the body due to aging, in addition to increased oxidative stress. Given that oxidative stress may play a key role in the age-related decline in egg quality, many studies have demonstrated through animal experiments that antioxidant treatment can improve egg quantity and quality. It was found that after 12 months of L-carnitine antioxidant treatment in mice, the number of sinus follicles increased significantly compared to controls, spindle and chromosome abnormalities were significantly reduced, and more litters were produced than in controls. In another study, acetylcysteine (NAC) was added to the drinking water of mice, and after 2 months of antioxidant treatment, the quality of fertilized eggs and early embryonic development were significantly better in the experimental group than in the control group. Although basic studies have shown that antioxidant treatment can delay oocyte aging and improve oocyte quality, the findings from clinical studies are not yet consistent. It is currently believed that antioxidants such as vitamin C, vitamin E, coenzyme Q10, L-carnitine, melatonin, and resveratrol may play a role in improving ovarian function and egg quality, and may be used as adjunctive medications in patients with advanced age and hypovarianism.