Night Lights Are Killing Us?

Man, what, are teddy bears next? The Lancet reports on a survey of studies that, combined, seem to show that night lights are causing cancer (registration required, but free):

Among the many different patterns of shift-work, those including nightwork are the most disruptive for the circadian clock.

Six of eight epidemiological studies from various geographical regions, most notably two independent cohort studies of nurses engaged in shift-work at night,2,3 have noted a modestly increased risk of breast cancer in long-term employees compared with those who are not engaged in shiftwork at night. These studies are limited by potential confounding and inconsistent definitions of shift-work, with several focused on a single profession. The incidence of breast cancer was also modestly increased in most cohorts of female flight attendants,4 who also experience circadian disruption by frequently crossing time zones. Limitations of studies in these flight attendants include the potential for detection bias, proxy measures of exposure, and potential uncontrolled confounding by reproductive factors and cosmic radiation.

Several different rodent models have been used to test the effect of disruption of the circadian system on tumour development. More than 20 studies investigated the effect of constant light, dim light at night, simulated chronic jet lag, or circadian timing of carcinogens, and most showed a major increase in tumour incidence.

OK, so it’s not literally night lights – it’s waking up in bright surroundings at odd hours, which throws off your circadian rhythms… which somehow leads to an increased risk of tumor growth. Having bright lights on at night shuts down the body’s secretion of melatonin, the sleepy hormone that also appears to fight cancer. Similar results have been found in people who’ve lost their pineal glands – the part of the brain that produces melatonin.

There’s a subscriber-only version (with well-linked references and sources) at Science News.

Sleep well.