Can you catch up on missed sleep?
Nicholas Eveleigh/Getty By Catherine de Lange DESPITE our best intentions, we don’t always get enough sleep. So what happens when we party until dawn or shave off a couple of hours each night? The need to sleep is controlled by a two-tier system. The circadian clock relies on light to keep your sleep/wake pattern within around 24 hours. Then there’s sleep drive or sleep pressure. The longer you are awake, the more a chemical called adenosine builds up in your brain, sending signals that increase your desire for sleep (see diagram). “After 16 hours it should be at a screaming level that means you have to fall asleep,” says Matthew Walker, who researches sleep at the University of California, Berkeley. “When you do, the pressure valve is released.” Caffeine keeps you perky by blocking adenosine receptors in the brain, but the effects of overriding the sleep drive quickly show themselves. Being awake for 24 hours will leave you with the same level of cognitive impairment as having a blood alcohol content of 0.1 per cent – more than the drink-drive limit in several countries. Chronic lack of sleep takes a toll, too. In one study, researchers followed students who slept just 4 hours a night for six nights in a row. They developed higher blood pressure, increased levels of the stress hormone cortisol and insulin resistance, a precursor to type 2 diabetes. They also produced half the normal number of antibodies in response to a flu vaccination. Fortunately,