Hence, healthy blood vessels are of crucial importance for proper erectile function. The focus here is on the endothelium, a thin layer of cells that line the inner wall of the blood vessels. Endothelial cells are the main protagonists in the regulation of blood flow, blood pressure and coagulation. There are indications that raised levels of oxidized LDL cholesterol, trigly-cerides and homocysteine in the blood may increase the risk of endothelial dysfunction (1). Consequently, if micronutrients with antioxidant effects are able to maintain a normal vascular tone by reducing vascular oxidative stress, this could be generally important for preventing vascular diseases and, more specifically, for preventing erectile function disorders.
Several studies have described the benefit of antioxidant vitamins C and E for improving general endothelial function in both healthy subjects (2) and in high risk groups (3, 4). Trials have also indicated that these vitamins could prevent endothelial dysfunction caused by raised levels of homocysteine in the blood (5). One recent study furnished evidence that vascular endothelial function could be dependent on vitamin D status: low blood levels of vitamin D were associated with vascular endothelial inflammation (6). Further-more, it has been demonstrated that food supplements with vitamin D can improve vascular endothelial function (7).
Additionally, blood flow is regulated by nitric oxide (NO), which causes blood vessels in the body to expand and thus lowers blood pressure. NO also relaxes the blood vessels in the penis, allowing the corpus caver-nosum to fill with blood in response to sexual arousal. Studies have shown that omega-3 fatty acids can stimulate endothelial release of NO. Moreover, antioxidants can increase NO production and delay NO breakdown. There are also indications that folic acid, vitamin C, vitamin E and calcium can support the biochemical processes leading to NO release. Certain food supplements could therefore favorably influence erectile function (8).
Another important feature of reproductive health is male fertility. Healthy and motile sperm is essential for this. Sperm contain a large number of mitochondria that provide energy, but that can also cause oxidative stress in these cells. It is imperative that sperm cells be protected against oxidative damage: it is postulated that 30 to 80% of male subfertility cases are due to the damaging effects of lifestyle-related oxidative stress (9, 10). Supporting the body’s own antioxidant protection through food supplements containing the relevant micronutrients can improve sperm quality in affected men (11, 12). Vitamin E (13) and coenzyme Q10 (14, 15) have been identified as particularly effective antioxidants for the protection of sperm; the former can even protect against the DNA damage that occurs when frozen sperm is thawed (16). Food supplementation with coenzyme Q10 and lycopene was also associated with improved sperm quality (17). Furthermore, there are indications that increasing the intake of selenium, an antioxidant trace element that appears to protect the proteins in the sperm cell membrane against oxidative damage, could increase the quantity and the quality of sperm (18). A sufficient supply of zinc and folate, which is involved in spermatogenesis, also appears to be important (19). Thus researchers found a link between increased DNA damage and a low concentration of folate in semen (20). Moreover, a variation (polymorphism) in the methylentetrahydrofolate reductase (MTHFR) gene, which has a central function in folate metabolism, could be the cause of an increased risk of idiopathic male infertility (21).
Vitamin A plays a key role in spermatogenesis. One study showed that aging men, men with an increasing body mass index and smokers have lower vitamin A and vitamin E concentrations, and that this, in turn, is associated with reduced semen quality (22).
Vitamin D, too, obviously influences male semen cells. The results of one study showed that higher vitamin D levels were associated with better sperm motility and an increase in intercellular calcium concentration (23). Furthermore, there are indications that a lack of vitamin D could be linked to impaired function of the testes which produce sperm and the male sex hormone testosterone (24, 25).
An adequate intake of long-chain omega-3 fatty acids (PUFAs) also seems to be essential for good sperm quality: the membranes of healthy sperm are plentifully supplied with PUFA. Since these fatty acids are very vulnerable to oxidative stress, they need antioxidants to protect them against damage (26). A lower concentration of PUFAs has been observed in the sperm of infertile men.
Further studies are needed to more accurately investigate the influence of micronutrients on male reproduc-tive health. Vitamins A, E, D and folic acid, as well as PUFAs, are generally among the micronutrients that are often difficult to adequately obtain from average dietary habits.