Many countries celebrate an afternoon siesta, closing shops for lunch and returning in the early evening to resume work after a snooze. In the United States, as many as a third of adults regularly take a midday nap, according to the National Sleep Foundation.

Experts say a short nap in the afternoon can yield many health benefits, from improving your mood to improving your memory. According to WebMD, a nap can be as effective as a good night’s sleep in helping you remember things you learned earlier in the day. Other benefits include improved immune function, lowered blood pressure, and boosted brain power.

According to Gabe Mirkin, M.D., in one study a 45-60-minute nap improved memory recall fivefold. “These results were supported by improved sleep spindles on an EEG brain wave test that signify better memory recalls,” he tells Newsmax. “Naps as short as 10 minutes can revive memory and alertness according to other studies.”

However, to be beneficial for most adults, naps should be short, say experts at the Mayo Clinic. Aim for 10 to 20 minutes only and take them early in the afternoon. Napping after 3 P.M. can interfere with nightly sleep patterns.

The problem with longer naps is that most folks wake up groggy suffering from what the Mayo Clinic calls, “sleep inertia.” Also, people who experience insomnia or poor sleep quality may find that napping exacerbates their problems.

Mirkin, author of The Healthy Heart Miracle, points out that some studies show that people who take naps lasting longer than two hours are far more likely to suffer serious heart disease than those who take shorter naps or no naps at all. And experts at Harvard Medical School add that adults who take long naps during the day may be more likely to have conditions like diabetes and depression.

They add that the urge to sleep during the day may signal that you aren’t getting sufficient, quality sleep at night, which is associated with a higher risk of these conditions. Daytime drowsiness may also be caused by a sleep disorder.

Napping during the day can set up a vicious cycle, making up for lost sleep and then finding yourself unable to fall asleep at bedtime because you slept during the day.

“Limiting naps is one strategy to improve overall nighttime sleep,” says Suzanne Bertisch, M.D., of the Brigham and Women’s Hospital in Brigham, Mass., who is a sleep specialist and adds that large studies have found that napping can have both benefits and harms, depending on the individual.

“If you need to nap during the day, it is important to assess why you may be sleepy enough to fall asleep during the day, especially if you nap regularly,” she says. Track how much sleep you are getting at night. If you aren’t getting enough, improve your sleep habits. The Sleep Foundation has tips to help improve your sleep hygiene.

“If you are already getting at least seven or more hours of sleep at night and are still tired during the day, discuss this with your doctor,” says Bertisch.