Jet lag: a cancer-hazard sleeper?

Epidemiologist Anthony R. Mawson of the Carolinas Health Care System in Charlotte, N.C., hypothesizes that jet lag leads to an increased risk of breast cancer. In the Aug. 22 Lancet, Mawson describes his unusual, untested theory.

A 1995 study showed that Finnish flight attendants had an increased risk of breast cancer, Mawson points out. He wonders if that risk might be attributable to jet lag, as flight attendants frequently cross time zones and suffer a disruption in sleep-wake cycles as a result.

Jet lag interferes with the normal workings of the brain's pineal gland, which produces the hormone melatonin. Indeed, people who try to sleep during daylight hours decrease the gland's secretion of melatonin. Mawson suggests that a drop in melatonin may boost the threat of breast cancer.

"There's quite a bit of data linking melatonin to breast cancer," Mawson says. For example, some studies show that melatonin inhibits the growth of breast cancer cells in the laboratory.

The theory would be easy to test in a large study of female flight attendants, Mawson says. Until such a study is conducted, however, the relationship between this hormone and breast cancer remains cloudy.