Women who smoke cigarettes inhale a toxin that can trigger ovarian failure, significantly decreasing their reproductive years, scientists said on Sunday in the first study confirming a long-suspected link between smoking and female infertility.
Researchers led by Dr. Jonathan Tilly of Massachusetts General Hospital in Boston said a chemical found in cigarette smoke and some air pollution can trigger early menopause by accelerating the destruction of the egg cells in ovaries.
Tilly and his colleagues studied the effect of Polycyclic Aromatic Hydrocarbons, known as PAH, on female mice over a six-year period. They injected the mice with the toxin and tracked a chain of chemical reactions that triggered the death of the rodents' egg cells.
The toxin attaches to receptors on the surface of the egg cells inside the uterus. That bond triggers a chemical reaction that programs the eggs to die, the study found.
After confirming the effect the toxin had on the mice's egg cells, the scientists placed human ovary tissue under the animals' skin. The eggs began to degenerate within three days after the toxin was injected, the study found.
Tilly said the destructive process is gradual and cannot immediately be detected.
"You don't see any impact [from the chemicals] until many years down the road. The ovaries will continue to work, and the destruction will go on for a while, and boom," Tilly said in a telephone interview.
The findings were published in the journal Nature Genetics.
The toxin forms during the incomplete burning of coal or other substances such as charbroiled meat. PAHs also are used to make tar, some medicines, plastics and dyes.
"It is accurate to refer to them as silent killers because they damage a population of cells, [which] we can't deter until after the fact when it's way too late," Tilly said.
When girls are born, they have a finite supply of eggs that mature and are gradually released during ovulation. Continual exposure to the chemicals causes the eggs to die prematurely, resulting in early menopause, the researchers said.
The average woman begins to experience menopause in her late 40s or early 50s.
Tilly and other scientists are exploring ways to stop or reduce the role these chemicals play in egg destruction. One possible approach being studied involves preventing the receptors on the surface of the egg cells inside the uterus from bonding with the toxin.
"It is certainly a possibility, designing easy ways to protect egg cells is the thrust of our work," Tilly said. "We, in theory, should be able to intervene in that quite nicely."
Researchers also are studying the possibility that smoking by a pregnant woman could damage the ovaries of her developing female fetus and reduce the number of egg cells the child produces in her body.