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Smoking and Reproduction
Nov 1, 2013

Harming our bodies or health is a betrayal against this incredible gift. One of the major ways people harm the body is through smoking cigarettes.

Smoking harms human health in countless ways. It is one of the main causes of many diseases, such as lung and throat cancer, along with cardiovascular and respiratory track diseases, such as chronic bronchitis. According to the latest report from the World Health Organization, smoking remains the fourth of the top ten risks that threaten human health. Approximately 20-30% of adult fatalities are caused by ailments contributed to by smoking. Recent studies have shown the negative effects smoking has on human reproductive functions.

Effects on fallopian tubes

Smoking has a negative impact on female reproductive organs; this impact is determined by how long, and how much, a woman smokes. It may cause infertility by damaging the fallopian tubes that serve as a ground for the egg to be fertilized by sperm. In many studies, the risk of damage to the fallopian tubes was very high – this danger increases if a woman starts smoking a pack a day before the age of 18.

Effects on female hormones

Many toxic substances in cigarette smoke, including nicotine, directly inhibits the activity of the enzyme called aromatase, which plays a major role in the synthesis of the female hormone (estrogen) in the ovaries. Depending on the biological function, estrogen can be found in three different forms: as estrone, estriol and estradiol. Polyaromatic hydrocarbons found in cigarette smoke stimulate the microsomal cytochrome P-450 enzyme system that degrades hormones in the liver and, consequentially, increases conversion of estradiol with high biologic activity into estriol with the lowest activity. Alkaloids, one of the harmful substances found in cigarette smoke, were discovered to prevent production of progesterone in the ovaries. This plays a role in preparing the womb and in continuation of the pregnancy during the first three months. Therefore, smoking leads to progesterone deficiency during the early stages of pregnancy, causing miscarriages.

Effects on the maturation of the egg

The concentrations of the FSH hormone that is involved in the maturation of reproductive cells in the ovaries are especially high in young female smokers. In other words, a resistance develops against the FSH hormone in the ovaries and higher FSH hormone levels are required for the maturation of the egg. Thus, fertilization problems and missed periods can occur because of an absent reproductive cell. During the treatment of such patients with insufficient egg cell maturation, there is a 50% decrease in the success of the implantation (placement of the fertilized egg into the womb) and the continuation of the pregnancy in smokers when compared to nonsmokers. This means smoking significantly reduces ovarian functions, and ovarian stimulation becomes inadequate at earlier ages in women.

The negative effects of smoking on the reproductive system are also observed during the implementation of reproduction methods such as in vitro fertilization and assisted fertility technologies. The presence of high androgenic hormone levels (pre-metabolites of gender related hormones: androstenedione, DHEAS and testosterone/SHBG) in female smokers has been found to decrease the possibility of pregnancy during in vitro fertilization efforts.

Effects during pregnancy

There are many harmful consequences of smoking during pregnancy, especially for older women who are pregnant. Some of these consequences are premature birth, miscarriage, retardation of development, inadequate baby weight, perinatal mortality, ectopic pregnancy, placental praevia, and placental abruption. Placental praevia is the abnormal placement of placenta in the womb. In this case, depending on the excessive bleeding that occurs after the eighth month of gestation, the lives of the mother and fetus become imperiled, and fetal development is hindered. Placental abruption occurs depending on the premature separation of placenta from the womb, causing excessive bleeding that can also endanger the lives of the mother and baby.

In pregnant smokers, the postnatal ratio of infant mortality and disability increases as a consequence of deficiencies involving lung function and nerve development. These effects are directly proportional to how much a woman smokes. There are also negative impacts when a pregnant woman is exposed to second hand smoke by a spouse or close friend. Harmful metabolites of nicotine reach the baby via the placenta. Furthermore, nicotine is degraded slowly in the liver of a pregnant woman. Inadequate baby weight is related to smoking dosage and time.

Due to smoking in the early stages of pregnancy, the hormone levels of estriol, estradiol, progesterone and hCG, hPL which is secreted from the placenta, have been found to decrease. This reduction, which is observed in parallel with the amount of smoking, can result in miscarriages.

Toxic polyaromatic hydrocarbons have been found to accumulate at elevated ratios in the wombs of women who were exposed to cigarette smoke for a long time. During pregnancy, this situation leads to the deterioration of sertoli cells located in the reproductive glands of male fetuses. These glands assist in sperm production during adulthood, and damage to them can therefore cause a reduction in sperm generation.

An insufficient placental development occurs because of the negative effects of nicotine, cadmiums, and polyaromatic hydrocarbons damage the reproduction of trophoblast cells that make up the placenta. This situation explains the increasing miscarriage ratios among female smokers.

The free T4/TSH ratio in the serum of the umbilical cord, which connects the fetus to the placenta, increases in the babies of smokers compared to those of nonsmokers. This means that in babies of smokers, the thyroid glands may become overactive during birth. Depending on a mother's smoking habits, this hyperactivity of the fetal thyroid increases the metabolic speed and the amount of consumed oxygen in the body, thus leading to the inadequate development of fetus.

Menopause occurs two-to-four years earlier due in women who smoke, as compared to non-smokers. This is due to the aging of the eggs. The risk of entering menopause before the age of 45 in women who quit smoking at least ten years prior is 87% less than smokers who don't quit. Therefore, the earlier a woman stops smoking, the lower the risk of early menopause.

Effects of smoking on men

In research studies, it has been discovered that smoking has many harmful effects on testicular development and functions. These effects can be summarized as follows:

  • Reduction of semen volume and quality, increase in its adhesiveness, delay in its becoming liquid, and resulting deformation of the sperm.

  • Reduction in the number and mobility of sperm cells.

  • Delayed sperm nucleus maturation, deteriorated DNA integrity.

  • Decrease in the production of testosterone from Leyding cells.

  • Decrease in the egg fertilization capacity of the sperm.

As a consequence of these negative effects, male infertility can occur. As the amount of daily cigarette consumption increases, the number, strength, and types of anomalies also increase. In a study conducted in 2010, smoking has been showed to decrease zinc levels in the seminal plasma. As a result of this decrease, oxidative agents populate and DNA breaks take place, thus causing a disruption of sperm functions and infertility. Zinc deficiency at the same time leads to the destruction of seminiferous tubule cells where sperm cells are produced. Paternal smoking generates negative results during the application of assisted fertility methods (such as in vitro fertilization). The damage in the sperm DNA of the father can disrupt the embryo development. The risk of anomalies, cancer, and genetic diseases increases for the fetus.

Cigarette smoking clearly occupies a position as one of the worst enemies of mankind because of its destructive effects on the body. In this case, it does not make any sense to try finding excuses for smoking, for it is harmful to the body that has been loaned to us as a gift and a temporary property.

Cihanoglu is a professor of medicine in KATU, Trabzon, Turkey.