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The magic bullet

An occasional restless night is nothing to worry about, but a continuous lack of zzz's can hamper your immune system's ability to function. Though experts often say that sleep requirements vary by individual, a 2009 Carnegie Mellon study found that anything short of seven hours nearly triples your odds of catching a cold—and that means seven straight hours, with no middle-of-the-night wake-ups.

"For many of us, the only quiet time we have to think through things is when we're lying down at bedtime. Unfortunately, problem-solving in bed interferes with sleep," says Leslie Swanson, PhD, a sleep specialist at the department of psychiatry at the University of Michigan, Ann Arbor.