Imagine being in a sauna for a few hours. Then imagine getting out of it and walking straight into a giant freezer for another few hours. Do this several times a day and continue the routine for a couple of months. Some people say that’s what spending summer in Japan is like.

Japan’s summer months are notoriously hot and muggy, which can lead to a range of health problems. Natsubate (summer fatigue) leaves people feeling tired, lethargic and/or sleep-deprived. Many people lose their appetite and become irritated, while others suffer digestive problems such as diarrhea, constipation and/or giddiness.

Originally referring to a condition brought on by prolonged exposure to the sweltering summer heat, these days natsubate starts early even in late June for some people, because of sudden changes in the weather and freezerlike air conditioning in trains, buses and buildings.

Dr. Takao Matsumoto, deputy director of Tokyo Rinkai Hospital in Edogawa Ward, Tokyo, who occasionally sees patients with heat-related illnesses, says summer fatigue is primarily caused by perspiration problems. Body temperature rises in hot weather, and the body tries to cool itself via perspiration. But when exposed to the heat for too long, some people’s bodies become incapable of making such adjustments.

Matsumoto noted that natsubate should not be taken lightly. If left unattended, it can lead to dehydra- tion, cramps and heat stroke.

“Many people start having problems when the temperature rises to around 25 degrees,” Matsumoto said. “Ideally, the temperature differences between outdoor air and indoor air should be kept within 5 degrees.”

So what can we do to avoid the summer’s perils? Matsumoto and other experts offer the following no-nonsense tips:

Carry clothes that are easy to put on and take off: Many offices are excessively air-conditioned. Bring a cardigan or a long-sleeved shirt to your office and wear it when you feel cold. To counter the air conditioning, some office workers nowadays bring to their offices a yutampo (hot-water bottle), which many Japanese traditionally use to make their futon warm in the winter. You can buy yutampo at a drug store for a few thousand yen apiece. Another tip is to ask your office to turn their air conditioning down (which conserves energy, too.)

Get enough sleep: It might sound elementary, but sleep is indeed essential to avoid and recover from natsubate. If you have problems going to sleep because of the heat, place a bag of ice on your pillow for a few minutes, or turn on an air-conditioner with a timer, making sure that it switches off after several hours. Turning air conditioning on throughout the night is often a cause of natsubate.

Work out regularly: People who can sweat effectively are less likely to suffer from natsubate because their bodies are better conditioned to accommodate temperature changes. Regular exercise can prepare people for that. It also helps them build stamina to survive the summer.

Diet is key

Keiko Kamachi, a registered dietitian and associate professor of nutrition at the Kagawa Nutrition University in Tokyo, meanwhile, says a regular, balanced diet is key to staying healthy through the summer.

“Eat three meals regularly,” she said. “You can also choose to have food that makes you less likely to feel tired.” Summer vegetables such as tomato, eggplant and cucumber contain antioxidants that help protect against ultraviolet light, Kamachi says. Local summer fruits such as suika (watermelon) and nashi (pears) are rich in the minerals that are lost due to perspiration. Natsumikan (summer tangerine), rich in potassium and magnesium, is also good because its citric acid helps people recover from exhaustion, she said. The key, however, is not to gorge on any particular food item but to “eat a little bit of all (of them),” according to Kamachi.

When you are tired, try taking B vitamins, as they help the body convert food into energy, both Matsumoto and Kamachi say. Not that popping a pill is going to work magic.

“Vitamin supplements can irritate the stomach, so it is better to get B vitamins through regular food,” Kamachi says.

Foods rich in B vitamins include pork, soybeans and milk. Soba noodles are also known to be rich in B vitamins, she said, noting that when you have soba, you should also drink the sobayu (the hot water used to boil the noodles) served at most soba restaurants after the meal.

The use of food to ease summer exhaustion dates back to the eighth century in Japan, when the poet Ootomono Yakamochi recommended a suffering friend eat eel to regain his strength, and people in different regions of the country have developed their own particular remedies, often using food locally grown or produced. Junko Yokota, a travel consultant who lives in the Aizu region in western Fukushima Prefecture, says that it has long been a common practice for families in her area to pick ume plums that naturally grow in their gardens and put them in jars with rock sugar. Local plums a brand known as Aizu-takada ume make great plum juice, she says, noting that, when she was a girl, her grandmother would make her drink a glass of the homemade nectar every day during the summer.

“Plums are picked in June and placed in jars, and a year later they are ready to be served,” Yokota said. “You would drink the juice, and then eat the plum as well. It’s probably thanks to those plums that I have never experienced natsubate.”

Stay cool as a cucumber soup

Suffering from the heat? Want to try a Japanese solution to a Japanese problem?

Masahiro Kumamoto, a 46-year-old owner of a seafood-products store in Miyazaki Prefecture, western Japan, says he cannot do without a bowl of hiyajiru (cold miso soup poured over cold rice), to deal with the region’s notoriously hot summer. It has traditionally been a “work-time dish” among farmers and fishermen. A self-confessed hiyajiru otaku (obsessive fan), Kumamoto, whose store is named Kumaya Shokuhin, offers the following recipe for hiyajiru, which he claims, if properly cooked, is a culinary experience as rich as the French soup vichyssoise.

The method

1. Choose the type of fish you want to use. The most common fish used in many households is iriko (dried small fish). Fry the iriko in a pan, then crush them with a mortar. You can also use hiraki (fish cut open and dried), in which case grill them and separate the flesh from the bones.

2. To create a soup, fill a sauce pan with water, add katsuobushi (dried bonito shavings) and kombu seaweed and let the water boil for a few minutes.

3. Spread miso on tin foil and heat it for several minutes, giving it a nice roasted flavor.

4. Put the fish and some mashed-up tofu into the soup and bring it to the boil. Add the miso little by little, using a touch more of the paste than usual, because sliced cucumber (to be added later) thins out the taste.

5. Now the most time-consuming part: Let the soup cool to room temperature. Add the cucumber, chopped oba (Japanese basil) and ground sesame seeds. Prepare a portion of rice as usual.

6. Cool the soup in the refrigerator for at least an hour. Cool your rice to room temperature. Finally, don’t forget to chill your rice bowls in the refrigerator.

KEYWORDS Japan heat wave