Your Memory is Wiped
A study in Sleep found that people's accuracy on working-memory tasks dropped by about 15 percent while they pulled an all-nighter. Sleep helps your brain consolidate information, so without that recovery time, you're unable to file away important data.
Your Waistline Expands
"Some research has suggested that sleep restriction over many years may affect metabolism, increasing the risk of obesity and type-2 diabetes," says Siobhan Banks, Ph.D., an assistant professor of psychiatry at the University of Pennsylvania. In fact, a 2007 Canadian study found that people who sleep only five or six hours a night increase their likelihood of being overweight by 69 percent, compared with those who habitually sleep seven or eight hours.
You Get Sicker
University of Chicago researchers found that antibodies in sleep-deprived people who'd received a vaccine were about 50 percent weaker than those in well-rested people. Wake up early for that flu shot and it may not protect you so well. Harvard researchers also found that blood levels of C-reactive protein, a marker of heart-disease risk, can spike if you skip the sheets for just a few hours.
Your Cancer Risk Rises
During sleep your body produces melatonin, a hormone that helps regulate your sleep cycle. Interrupt sleep and you interrupt melatonin synthesis, which can be a problem. A 2007 University of Texas study review concluded that not only does melatonin detoxify harmful, cancer-causing free radicals, but in doing so it actually creates more antioxidants. Melatonin may also boost the effectiveness of vitamin C, another antioxidant. A good snooze could goose your morning OJ's potency.