Eating large meals at dawn and dusk in observance of Ramadan can reset a person’s biological clock. (SHAYNA BRESLIN/ASSOCIATED PRESS)

For millions of Muslims worldwide, the holy month of Ramadan is a time for cutting back. Daily fasting, a tradition that involves eating and drinking only before sunrise and after sunset, is meant to take attention off worldly indulgences and refocus energy into worshiping God.

But fasting can be taxing healthwise, particularly when Ramadan, which follows the lunar calendar, falls in August. During the holy month, which this year began Aug. 1, temperatures in the Washington area occasionally creep over 100 degrees and daylight lasts more than 13 hours. Studies show that fasters tend to experience more headaches, fatigue and daytime dehydration than usual; the long, hot days of August can compound those issues, especially for anyone working outdoors.

“In the U.S. we have air conditioning everywhere, but if you are a construction worker or you’re working outside all day, [fasting] is very difficult to do,” said Syed Rizvi, who has observed Ramadan for many years. “The day is so long and hot this year,” said Rizvi, chief of psychiatry at Upper Chesapeake Medical Center in Har-ford County. “At the end of the day you don’t even worry about the food, you worry about the water.”

Talat Benson, a Southeast Washington resident who emerged from afternoon prayer service at Masjid Muhammad in Northwest on a relatively cool and breezy day recently, noted that “you don’t want to do too much. You want to make sure it’s easy on yourself.”

While daytime hunger and thirst are just the most obvious consequences of the Ramadan fast, there can also be more subtle health effects, said Qanta Ahmed, an associate professor of medicine at the State University of New York at Stony Brook who studies sleep disorders.

Several studies have shown that people’s sleep patterns change during Ramadan. One small 2001 study in Morocco showed that not only did it take the eight participants longer to fall asleep during the month of fasting, but they also generally got less dream sleep or deep sleep, which is often needed to feel fully rejuvenated the next morning.

Ahmed, who has fasted during Ramadan for 12 years, said she observed similar changes in her own sleep patterns, but until she read the study recently she had not made the sleep-Ramadan connection. She said many people tend to overlook such small but important changes.

Eating large meals at dawn and dusk instead of three balanced meals throughout the day can reset the body’s biological clock, which affects the “ability to time your body temperature and your sleep,” she said.

Muslim populations in some countries change their work schedules to accommodate daytime fasting. Stores are often open later for people to run their errands, for instance, and those with full-time jobs try to adopt lighter schedules, said Ahmed, who has worked in Saudia Arabia.

But countries where Muslims are not a majority, including the United States, are not as accommodating, she said. Ahmed said she tries to take naps throughout the day to catch up on lost shut-eye. Rizvi said he finds the first week of his fast “difficult, but you kind of adjust to it” after that.

Some Muslims who fast say there can be health benefits and not just costs.

Jerome Johnson, 29, of Northwest, said he tends to eat less overall during the fast. He also mostly stops smoking for the month. Although he normally smokes around three cigarettes a day, he has only touched one or two since Ramadan started.

Ahmed said she loses eight to 12 pounds each Ramadan.

The Koran advises those who aren’t young, fit and healthy during Ramadan to forgo the daily fast and either make it up at a later date or give to charity. Several Muslim doctors said they advise patients with chronic illnesses and those who are pregnant or nursing babies to not fast.

“There are people who have conditions that make them critically ill or seriously ill, where going without food would be harmful for them,” said Saleem Arshed, a holistic health coach in New Jersey. He said he has clients with such chronic illnesses as diabetes who nonetheless want to fast for Ramadan.

Arshed said he can help most of them adjust their diets so they are able to fast without damaging their health, but he has come across a few exceptions. “If they’re in a condition where it’s really critical, I usually recommend that they not fast,” he said.

But for many Muslims, the spiritual benefits make the Ramadan fast worth doing. “A lot of Muslims actually consider it as a gift,” Rizvi said. “They get an extreme sense of accomplishment and sense of satisfaction” from observing Ramadan.