While you sleep you are not simply chilling. New findings by Harvard researchers at Brigham and Women's Hospital show that a vast number of hormonal changes and neurochemical reactions occur only while you sleep, and many of these have serious implications for your weight, health and level of fitness. This is why you can't compensate for missed sleep with coffee or vitamins.
"Research shows that you have fewer white blood cells in circulation when you sleep less," says Fran Mason, M.D., co-author of "The Force Program: The Proven Way to Fight Cancer Through Physical Activity and Exercise" and a physician who counsels elite athletes. "These 'natural killer cells' fight infection and represent the front line in your ability to ward off illness. They function best when you make your numbers regarding sleep." She recommends 7-8 hours of sleep a night for adults.
"Meanwhile, markers of inflammation go up as you sleep less," says Mason. Inflammation can be particularly problematic for athletes, causing pain, muscle soreness, arthritis, tendinitis, and other muscle and skeletal problems. Internally, inflammation is linked to asthma, heart disease and a number of other health problems.
Mason points out that sleep deprivation and obesity are often bedfellows because two weight-regulating hormones -- ghrelin and leptin -- are greatly controlled by the amount of time you sleep.
"Ghrelin rises between meals and falls rapidly right after you eat," Mason says. "Ghrelin levels elevate slowly as you sleep; when you don't sleep, ghrelin levels rise more sharply, by as much as 15 (percent) to 28 percent."
Research has linked this increase to a bigger appetite and to weight gain of as much as 5 to 15 pounds.
"Leptin sends messages to your hypothalamus, indicating your total body fat stores," Mason says. "The higher your levels of leptin, the higher your energy stores are perceived to be, and the lower your hunger and appetite will be. Leptin levels increase when you're eating excess calories. Leptin levels also rise when you sleep. When you cut back on sleep, your leptin levels drop almost 20 percent."
This drop due to lack of sleep is perceived by your brain the same way a 30 percent reduction in your caloric intake would be. And it produces the same appetite you'd have if you had cut your food intake by nearly a third. Other studies show that an appetite for calorie-dense foods with high fat and carbohydrate content are elevated when you are sleep deficient.
Sleeping less also alters your thyroid metabolism by decreasing your pituitary gland's production of thyrotropin, a thyroid-stimulating hormone. This may be linked to subtle changes in your resting metabolic rate during the day.
Another bioactive molecule that is altered when you miss sleep is human growth hormone (also known as somatotropin), which helps you maintain muscle mass by promoting protein synthesis, metabolizing fat, and promoting electrolyte and fluid balance. It's produced by your pituitary gland, mostly at night, usually during early deep sleep in lean, well-nourished adults.
Growth hormone deficiency in adults causes abdominal obesity, muscle weakness and a change in body composition. Growth hormone decreases naturally with age, but you can lessen its decline and improve your body composition, muscle mass and strength simply by getting enough sleep. Proper exercise also causes the secretion of more growth hormone, which increases your bone metabolism and metabolism in general, thus bolstering your lean body mass even more.
As you exercise more frequently, you'll need more sleep. But if you don't work out too late in the day, it will also help you sleep better at night.
Eric Heiden, M.D., a five-time Olympic gold medalist speed skater, is now an orthopedic surgeon in Utah. He co-authored "Faster, Better, Stronger: Your Fitness Bible" (HarperCollins) with exercise performance physician Max Testa, M.D., and DeAnne Musolf. Visit www.fasterbetterstronger.com.