Longer days — at least for me — mean time for long evening workouts, but I need to be careful. Enthusiasm for exercise is fabulous, but athletes can sabotage their fitness goals if it causes them to hit the sack much later.
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 have serious implications for your weight, health and fitness. This is why you can't compensate for missed sleep with coffee or vitamins.
Blood and sleep
In another study, the number of antibodies in the bloodstream produced in response to the flu vaccine was lower after six nights of partial sleep deprivation.
"Research shows that you have fewer white blood cells in circulation when you sleep less," says Dr. Fran Mason, 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 frontline in your ability to ward off illness. They function best when you make your numbers regarding sleep." She recommends seven to eight 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.
Weight and sleep
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.
Hormones and sleep
Sleeping less also alters your thyroid metabolism by decreasing your pituitary gland's production of thyrotropin, a thyroid-stimulating hormone.
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-wrote "Faster, Better, Stronger: Your Fitness Bible" (HarperCollins) with exercise performance physician Max Testa, M.D., and DeAnne Musolf. Visit fasterbetterstronger.com.