Night falls, so you flick on your lights. But a shocking theory has been gaining support in the past few years: that artificial light at night may contribute to breast and prostate cancers, perhaps because it turns down production of the hormone melatonin. Now two studies add weight to that idea.
One, from Israel’s University of Haifa, analyzed satellite measurements of nighttime light and cancer rates in 164 countries. The most brightly lit had the highest rates of prostate cancer, more than double those in the dimmest nations.
Meanwhile, Harvard researchers who tracked more than 18,000 postmenopausal women reported that those with the lowest night time levels of melatonin were about 60 percent more likely to develop breast cancer.
It’s known that light suppresses the brain’s production of melatonin. The hormone may play a role in immunity or help slow the growth of cancer, according to Richard G. Stevens, PhD, a coauthor of the Israeli study. So how can you minimize the possible risk posed by modern lighting — without going preindustrial?
- Sleep in as dark a room as possible. Use room-darkening blinds or shades if you live on a bright, urban street or have a streetlamp outside your window.
- Keep a night-light in the bathroom for midnight visits instead of turning on the overhead. Even brief exposure to light can suppress melatonin. A red bulb is best: Red wavelengths cause a less precipitous drop in levels of the hormone than blue wavelengths, such as those in halogen and fluorescent lighting.
- Eat breakfast by the window. A 20-minute dose of sunlight will reset your natural circadian rhythms and help ensure a healthy night time melatonin peak.