**4. The multifaceted role of vitamin C as a powerful antioxidant**

Antioxidants constitute molecules capable of impeding or decelerating oxidative harm inflicted upon cells by free radicals. Free radicals, characterized by their instability, pose a threat to cellular integrity and are implicated in the onset of diverse ailments, encompassing cancer, cardiovascular diseases, ovarian damage, and neurodegenerative disorders. Antioxidants function by neutralizing free radicals through the donation of electrons, thereby diminishing their potential to induce harm. The incorporation of antioxidant-rich foods and supplements into one's diet has been correlated with a myriad of health advantages. Antioxidants play a crucial role in alleviating reactive oxygen species (ROS) and providing protection against oxidative stress [37, 74–77].

Vitamin C is renowned for its robust antioxidant properties. This vitamin plays a crucial physiological role in safeguarding against various oxidative damage-related diseases, including cancer, atherosclerosis, heart attacks, strokes, arthritis, cataracts, and the aging process. These conditions are primarily driven by the presence of free radicals. One of the most intriguing aspects of vitamin C's function lies in its in vivo antioxidant effects. Its biochemical structure involves two oxygen atoms bound together by a double bond and three hydroxyl groups connected to its carbon atom. This structure allows vitamin C to act as a powerful antioxidant, protecting our cells from damage caused by free radicals [27].

Vitamin C is part of antioxidant complexes, collaborating with other nonprovitamin A carotenoids like vitamin E, β-carotene, lutein, and lycopene, in addition to flavonoids and selenium. However, it is important to note that debates regarding the results of clinical studies in this area persist. Another fascinating characteristic of vitamin C is its dual role-it can act as both a pro-oxidant and an antioxidant within cells, and this dual function depends on the concentration of vitamin C. The antioxidant role of vitamin C is multifaceted, employing various mechanisms to prevent lipid oxidation. It effectively neutralizes superoxide, hydroxyl radicals, hypochlorous acid, and other free radicals and oxygen-derived species by donating electrons to them. Furthermore, vitamin C converts into less reactive semidehydroascorbate and

dehydroascorbic acid radicals, effectively reducing oxygen and carbon-centered radicals [78]. Vitamin C is also capable of regenerating essential base antioxidants. Despite being hydrophilic and unable to penetrate the lipid environment of lowdensity lipoprotein (LDL), vitamin C enhances the action of lipophilic antioxidants by regenerating them. For example, it elevates plasma levels of β-carotene and vitamin E, safeguarding LDL from oxidation by converting tocopherol radicals into their reduced, antioxidative form. Due to these remarkable effects, vitamin C is often lauded as both an anticarcinogen and a protector against atherosclerosis [56, 79].

Vitamin C's significance extends beyond its antioxidant properties. Its potent electron transfer capability plays a pivotal role in various aspects of cellular function and health [80]. It actively participates in immune responses, cellular metabolism, and enzymatic reactions, while also contributing to the maintenance of the body's redox balance [81]. The effectiveness of the immune system relies on a resilient and wellprotected redox system, in which vitamin C plays an essential role [45]. Furthermore, vitamin C is recognized for its capacity to effectively scavenge free radicals in both plasma and cell membranes. It can also elevate nitric oxide levels through oxidative defense and endothelial nitric oxide synthase activity [82].

Vitamin C's benefits extend to skin health as well. Studies have shown that both dietary intake and supplementation of vitamin C increase its presence in skin cells and enhance the skin's antioxidant defense mechanisms [83, 84]. Daily supplementation with 500 mg of vitamin C has been reported to maintain adequate levels of reduced glutathione (GSH) in the bloodstream, enhancing overall antioxidant defense [85].

Several studies have suggested a potential relationship between ascorbic acid and female fertility [86]. Levine and Morita found that ascorbic acid deficiency may contribute to infertility by causing atrophy of ovarian follicular atresia and premature resumption of meiosis [87]. Therefore, maintaining sufficient antioxidant concentrations is crucial to protect oocytes and all follicles from excessive ROS and, consequently, oxidative damage. This is of paramount importance in preserving gamete quality and supporting reproduction within the reproductive systems [88].
