by Alison O'Donoghue

Created on: July 01, 2008

Cigarette smoking and its effects on semen quality

The association between cigarette smoking and semen quality has been extensively studied in studies conducted across the world. Interestingly, the results of these studies are not consistent while some trials have found an association between cigarette smoking and impaired semen quality, in others, no link has been identified. Some investigators have found current smoking to have most impact on semen, whereas others conclude that maternal smoking has a greater influence.

What constitutes normal semen quality?

World Health Organization parameters are used to define normal semen characteristics. The volume of the ejaculate should be more than 2 ml, the sperm concentration should be more than 20 million/ml and, at least 50% should be moving normally. Less than 15% should have abnormal forms and there should be less than 1 million white blood cells per ml of ejaculate.

How does smoking affect semen quality?

The mechanism behind the deleterious effects of smoking on semen quality is not fully understood. It may be due to any or all of the following: (1) an impact on levels of hormones such as testosterone; (2) a reduction in blood supply to the testicles; (3) a direct toxic effect upon sperm from the many chemicals in cigarette smoke, leading to sperm DNA damage.

Study results are conflicting

A large study in Denmark examined the relationship between smoking and semen characteristics and hormone levels in a cohort of more than 2,500 healthy men (Ramlau-Hensen et al, 2007). The sperm concentration, the semen volume, the total sperm count and the percentage of motile sperm all decreased as number of cigarettes per day increased. After adjusting for other factors which might impact on semen quality, men who smoked more than 20 cigarettes per day had a 19% lower mean sperm concentration and a 29% lower total sperm count than non-smokers. Interestingly, another large study performed in normal healthy men in 5 European countries including Denmark found no association between current smoking habits and semen quality (Jensen et al, 2004). However, the study investigators found than men who had been exposed to cigarette smoking in utero had reduced sperm concentrations and sperm counts, a smaller testis size, and fewer motile and morphologically normal sperm compared with men who had no smoking exposure before birth.

The effect of cigarette smoking on semen quality has also been studied in men undergoing fertility investigations. In a study in Switzerland (Kunzle et al, 2003), cigarette smoking was associated with a significant decrease in sperm density, total sperm count, total number of motile sperm and percentage of normal sperm forms.

The best approach?

While further studies are needed to definitively assess the effect of cigarette smoking, it seems sensible to advise men to abstain from smoking to avoid possible impairment of fertility, especially if they are part of an infertile couple, and to advise pregnant women to avoid smoking, not only because it may cause adverse birth outcomes, but also because the reproductive health of the child may be affected.

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