Where no medical reason is diagnosed for infertility, modern science assumes that infertility is primarily caused by diet and lifestyle.
Being 10kg overweight increases the risk of infertility by 10%. Particularly the increase in abdominal fat leads to a reduction of free, biologically active rate of testosterone.
Smoking affects sperm density, sperm motility (movement) and sperm morphology (appearance). A direct effect on testicular function and spermatogenesis is suspected. Metabolites of cigarette smoke components may induce an inflammatory reaction in the male genital tract, which in turn can result in oxidative damage to the sperm due to reactive oxygen radicals.
Severe chronic alcohol abuse can be directly toxic to the testes. It manifests itself in spermatogenesis arrest including Sertoli cell-only syndrome as well as abnormal sperm motility and morphology
Dietary deficiencies can lead to the development of nutritional deficiencies and subsequently to reduced sperm quality. Vitamins and micronutrients, in particular, which the body must get from food, serve as a cofactor for the enzyme reactions and have an antioxidant effect.