Infertility is defined as the failure to achieve pregnancy after at least 12 months of regular, unprotected sexual intercourse. About one in seven people in Europe is infertile. Of these, 35-40% are women, 35-40% are men and 10-20% are mixed (both men and women).
Although the most common factors in infertility are tubal factor, endometriosis, polycystic ovary syndrome, ovulation disorders, age etc. (in women), and erectile dysfunction and abnormal semen parameters (in men), lifestyle and daily habits also affect the fertility of both men and women, as well as the fertility of the children who are born.
Smoking is one of the most common human habits and remains a global phenomenon. According to the World Health Organization, 30% of men over the age of 15, and 40-50% of men of reproductive age (20-40 years), are smokers. In women, these rates are roughly similar.
The negative effects of smoking on health, such as on the cardiovascular and respiratory systems, are well known, but many people do not realise that smoking also affects fertility.
Many studies report an association between smoking and delayed conception in couples where the man smokes. Smoking affects semen parameters such as motility, morphology and concentration of spermatozoa through oxidative stress and the damage caused to sperm DNA. Interestingly, male fertility can be affected even when semen parameters are normal.
Components of tobacco smoke, such as nicotine, cadmium and carbon monoxide, have been associated with increased oxidative stress in spermatozoa.
Also, direct toxic damage to the testes in smokers can affect the normal function of the hypothalamic-pituitary-gonadal axis, leading to disruption of endocrine function and spermatogenesis in the testes. Smoking affects the secretory function of the Sertoli and Leydig cells in the testes, thereby causing the reduced semen quality observed in smokers.
Smoking, both active and passive, has been shown to be capable of causing erectile dysfunction.
Varicocele is the abnormal dilation of the venous plexus near the upper and lateral part of the scrotum. It is very common, found in about 15% of the general male population and in about 40% of infertile men. The combination of smoking and varicocele is associated with a semen effect 10 times greater than that observed in men who have a varicocele but do not smoke, and a five times greater effect in men who smoke but have no varicocele.
Women who smoke need more time to achieve pregnancy compared with the rest of the population. Infertility rates among female smokers are roughly double those among non-smokers. This is because the components of tobacco affect ovarian function and therefore egg quality, as well as endometrial function.
There is also evidence that the reproductive period is shorter and that menopause occurs one to four years earlier in women who smoke. Smoking may reduce the frequency of the menstrual cycle, which can lead to endometrial dysfunction as well as ovulation disorders. Various toxins released during tobacco combustion have been detected and identified in the ovary and/or follicular fluid, as well as in the endometrial cells of smokers.
The effects of smoking on fertility also show up in assisted reproduction treatments, such as IVF. Women who smoke often need higher doses of medication during treatment, a smaller number of eggs is retrieved at egg retrieval, they have a lower fertilisation rate due to egg quality, and lower pregnancy rates compared with IVF patients who do not smoke.
Although more studies are needed to understand in depth the mechanisms by which smoking affects the fertility of men and women, it is considered advisable to encourage couples to stop smoking before they start trying to conceive.
Oxidative stress plays an important role in the pathophysiology of infertility. Studies of dietary supplements and antioxidants generally show a beneficial effect on ovarian and testicular function. However, their mechanism of action, as well as the optimal way and dosage of taking them, is unknown.