Sperm motility is one of the factors necessary for male fertility. Motility refers to the movement of sperm in a forward motion from vagina to the fallopian tube, where the egg is fertilized. In addition to smoking being a general health risk, studies in the lab and observed in humans show smoking reduces sperm motility. Limited clinical research exists on mechanism of action and future research presents a challenge due to the ethics of exposing nonsmokers to the harmful effects of smoking.
Sperm Motility
When pregnancy is not achieved within one year with unprotected sex, one of the infertility tests for males determines the quantity and quality of sperm, including sperm motility. Sperm movement relies on a biochemical reaction for propulsion of the tail. Factors associated with reduced sperm motility include reduced energy available, increased oxidative damage resulting in sperm defects and the presence in seminal fluid of leukocytes.
Toxic Substances
Tobacco smoke contains a mixture of approximately 4,000 chemicals, with several known to be toxic or carcinogenic. Research published in the "International Journal of Fertility and Sterility" in 2009, shows cadmium, nicotine and its metabolite cotinine reduce sperm motility in the laboratory. In addition to the toxic substances directly released from tobacco, oxidative damage from reactive oxygen species may damage sperm. According to a study published in "Fertility and Sterility" in 2002, male smokers seeking treatment for infertility at the Cleveland Clinic showed a 107 percent increase in reactive oxygen species levels in the semen.
Insulin-Like Growth Factor-I
The presence of certain factors in the male reproductive organs produce healthy sperm. According to a study published in "BJU International" in 2009, insulin-like growth factor-I in the semen is associated with the presence of motile sperm. The sperm collected from smokers in the study contained lower levels of insulin-like growth factor-I and fewer motile sperm.
Increased Leukocyte Activity
Higher leukocyte levels in semen correlate to both cigarette smoking and infertility. White blood cells, also called leukocytes, circulate in the blood to protect against infection or inflammation. According to a study published in "Fertility and Sterility" in 2002, leukocyte concentration in semen increased 48 percent in smokers. Although the mechanism of action remains undetermined, the authors suggest possible activation of the immune system by chemical mediators or the presence of defective sperm caused by toxic substances in cigarette smoke.
Lower Antioxidant Levels
Cells in the sperm membranes and around the flagella contain numerous double bonds susceptible to attack by reactive oxygen species. While the body produces antioxidant enzymes to protect against cell damage, antioxidant levels decrease in smokers. Research published in "Andrologia" in 2006, indicates reduced sperm motility may be associated with smokers' lower levels of the antioxidant ascorbic acid. A study published in "Biological Trace Element Research" correlated the increased presence of reactive oxidant species in seminal plasma from tobacco exposure with increased oxidative damage and corresponding low levels of glutathione, an antioxidant enzyme produced in the body.
Biochemical Reaction Changes
Sperm movement requires ATP and phosphorylating creatine shuttle to power the flagella, known commonly as the tail, for forward motion. According to a study published in "International Journal of Fertility and Sterility" in 2008, three particulates present in tobacco smoke inhibited creatine kinase activity in sperm samples. Exposure to cadmium resulted in a 65 percent reduction in creatine kinase activity. Nicotine produced a 44 percent reduction in creatine kinase activity and cotinine, the metabolite of nicotine, produced a 39 percent inhibition of creatine kinase activity.
References
- "International Journal of Fertility and Sterility"; In Vitro Inhibition of Human Sperm; MA Ghaffari, PhD et al; Nov-Dec 2008
- "Fertility and Sterility"; Effect of cigarette smoking on levels of seminal oxidative stress; RA Saleh, M.D et al; September 2002
- "BJU International"; Seminal plasma cotinine and insulin-like growth factor-I; A Hassan et al; June 2008
- "Andrologia"; Effect of smoking on seminal plasma ascorbic acid in infertile and fertile males;T Mostafa et al: December 2006
- Biological Trace Element Research; High Levels of Cadmium and Lead in Seminal Fluid; AR Kiziler et al; December 2007
