“Sleep that knits up the ravel’d sleave of care,” wrote Shakespeare, and it’s true; sleep refreshes our outlook on life, plus much more besides.

Recent research shows that sleep is essential to repairing physical wear and tear, from healing wounds to building the immune system. Chronic lack of sleep can cause depression and impaired thinking.

How much sleep is enough? Adults need 7 to 8 hours a day. What if you’re one of the 30 percent who have trouble getting that much? Imperfect and addictive medications (including alcohol) can offer temporary help, but you might try eating more carbohydrates before bedtime, or taking naps.

Carbohydrates, like the proverbial glass of milk, put sleep-inducing tryptophan into your bloodstream. And when you nap, you’re going back to the multistage sleep (“polyphasic sleep”) that was universal before the electric light, and still is in siesta-loving Latin countries.

NASA and the U.S. military have supported serious research at the University of Pennsylvania and elsewhere on the power of naps combined with 4 hours or more of “anchor sleep” to maintain successful performance. According to one report, “individual naps should be at least 45 minutes of sleep,” with the aim being to acquire “a daily total of 8 hours.”

If that can’t be done, a “sleep debt” may be significantly repaid by increased sleeping on weekends — but many of us already knew that.