Night falls, so you flick on your lights. But a theory has been gaining support in the past few years that artificial light at night may contribute to cancer, perhaps because it slows production of the the hormone melatonin. Now two studies add weight to the idea.
One, from Israel's University of Haifa, analyzed satellite measurements of night-time 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.
So how can you minimize the possible risk posed by modern lighting? Sleep in as dark a room as possible. Use blinds or shades if you live on a bright street. 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 of the hormone.