7 Most Convincing Reasons to Get 7 Hours of Sleep

Clock in your seven hours of shut-eye—no less—and avoid a striking 62 percent increase in breast cancer risk, finds an eight-year Japanese study of 24,000 women. The theory: Without adequate sleep, the light-sensitive pineal gland doesn't secrete enough hormone-regulating melatonin. That's a problem, because our bodies use melatonin to suppress the hormone estrogen—which, unchecked, may stimulate (cancerous) breast cell division.