Doctors have known for more than 20 years that smoking cigarettes can cause early menopause in women, leading to early onset of many health problems.

As this ScienCentral News video reports, researchers at Harvard Medical School have discovered exactly how chemicals in tobacco lead to lower fertility.

Baby on board

Every woman’s genetics and lifestyle combine to produce a unique body chemistry. Therefore, a woman might smoke without noticing any fertility problems and may get pregnant easily into her early forties. However, it’s possible that smoking during pregnancy can cause a fertility problem for her baby.

Chemicals found in tobacco smoke, known as polycyclic aromatic hydrocarbons (PAHs), activate a set of events in egg cells (oocytes) that lead to the cell’s death by a bursting process known as apoptosis. Dr. Jonathan Tilly, Director of the Vincent Center for Reproductive Biology at Harvard Medical School, found that PAHs killed the developing egg cells in the fetuses of mice. Tilly found that the pathway for this cell death is the same in humans as in mice, which he calls "clear evidence to indicate that [women who smoke during pregnancy are] damaging their unborn fetus."

A normal woman starts at birth with about one million immature eggs, about 70 percent of which die before puberty. Only 400 to 500 actually mature and are released during ovulation over the course of a woman’s reproductive years. A woman whose mother smoked while she was pregnant may have problems conceiving even if she herself never smoked, due to the smaller number of viable eggs she starts with at birth.

Not to mention that smoking during pregnancy increases the risk of low-birthweight babies, stillbirths, and infant mortality. Babies of smokers, whether their mothers smoke during pregnancy or after, also experience more lung problems and asthma than those born to non-smokers. Secondhand smoke from new fathers also affects pregnant women and their babies, so fathers shouldn’t consider themselves off the hook.

Lastly, all women—smokers or non-smokers—are exposed to PAHs in the environment. Many industries produce PAH byproducts, and car exhaust contains them as well. Tilly feels that environmental and occupational exposure to these chemicals is a small but not insignificant risk.

Those horrible hormones

Because these chemicals in tobacco smoke kill eggs, they can lead a woman to menopause earlier. Menopause occurs when a woman’s egg supply runs out and the ovaries stop producing estrogen and progesterone. When chemicals kill eggs early, a woman reaches menopause early. This may not seem like a problem (for some it may even seem like a blessing), except that the loss of estrogen brings about myriad associated health problems.

The loss of estrogen contributes to osteoporosis (bone weakening), heart disease, and eye disease such as glaucoma. Estrogen may help protect against some cancers, although it could also increase the risk of others.

Additionally, emotional symptoms like anxiety or depression can accompany menopause, as a woman can be devastated by the loss of her youth and ability to have children.