The summer we grew up with is not the summer we live in now

Why older bodies fail at heat, why most Japanese heatstroke deaths happen indoors, and the short protocol that keeps a household through the season.

The Japanese summer is different than it was when I was young. Not by feel — by the numbers. Tokyo’s average August temperature has risen about two degrees Celsius since the 1970s, and the frequency of days above 35°C keeps climbing. What used to be a hot summer is now an ordinary one, and what used to be an ordinary summer would today be considered mild.

None of this would matter much if human bodies had adjusted at the same pace. They haven’t, and older bodies especially haven’t. Heatstroke has become the largest weather-related killer in Japan, and the majority of the fatalities are people over 65, indoors, often alone. Most of them said, in the last coherent hours of their lives, some version of “I’m fine, it isn’t that hot.”

What follows is what I want every person over 65, and every family member of a person over 65, to know about this.

Why older bodies fail at heat

Five specific changes make heat regulation less reliable with age.

Sweat glands work less efficiently. You have as many of them as you did at forty, but they produce less sweat per stimulus, so the evaporative cooling that keeps a younger person safe doesn’t kick in as strongly.

The thirst signal weakens. The brain circuit that says “you need water” becomes muted. Older adults can be substantially dehydrated without any subjective thirst.

Total body water is lower. Muscle holds water; fat doesn’t. As muscle mass falls with age, so does your reserve of water. The same fluid loss that produces mild discomfort in a young person produces symptoms in an older one.

Heat perception itself becomes less sensitive. The skin’s sensors for temperature dull. You may not feel that the room is hot until your core temperature is already rising.

And medications complicate all of the above. Diuretics increase water loss. Blood pressure medications alter the skin’s ability to shed heat. Anticholinergic drugs reduce sweating. Most people on multiple medications are more heat-vulnerable than they realize.

The Japan Ministry of Environment’s heatstroke ambulance data shows that more than half of emergency transports for heatstroke are people 65 and over, and most of those cases occur indoors. This is not a story about people collapsing on the sidewalk. This is a story about people sitting quietly in their living rooms.

Prevention, in the order that matters

Drink water on a schedule

Don’t wait for thirst. Set a target — 1.2 to 1.5 liters of water a day, more if the temperature is above 30°C — and drink small amounts steadily throughout the day. Every hour, a glass. A bottle of water on the desk you have to see. A cup by the reading chair. Do not rely on the thirst signal.

Water with a pinch of salt, or oral rehydration solution, or lightly-salted soup, is more effective than plain water when it’s very hot, because you also lose sodium through sweat.

Use the air conditioner

The single largest preventable factor in Japanese indoor heatstroke deaths is refusal to run air conditioning. There’s a generational reluctance — the sense that it’s wasteful, or unhealthy, or something one endures. That reluctance is killing people every summer.

Run the air conditioner. Aim for a room temperature of 26 to 28°C. If the electric bill is a concern, note that emergency ambulance transport, hospitalization, and hospital care are all vastly more expensive than the cooling.

Combine the AC with a fan to circulate air more effectively. Set a nighttime timer so the room stays cool during sleep. The overnight hours are when many heatstroke deaths occur.

Time your outings

Early morning before the temperature climbs, or late afternoon after it starts falling. If you must be out at midday, wear a wide-brimmed hat, light-colored breathable clothing, and walk in the shade wherever possible. Rest frequently.

Check on your neighbors

Solo-living older adults are the highest-risk group. If you know an elderly neighbor, ring the doorbell during a heat wave. If a family member lives alone, call to check in each day.

Recognizing heatstroke

The early signs are easily written off as fatigue or ordinary discomfort. Do not.

• Dizziness, faintness on standing, or facial flushing.
• Muscle cramps, especially in the legs.
• Fatigue, nausea.
• Severe headache. Confusion. Vagueness in responses.
• Skin hot to the touch, and no sweating despite the heat.

The last one is particularly dangerous: when the body stops sweating in the heat, cooling has essentially failed. This is a medical emergency.

First response

1. Move to a cool place. AC-conditioned indoors, or deep shade at minimum.
2. Loosen tight clothing. Cool the neck, armpits, and groin — the large blood vessels near the surface — with ice packs or cold wet towels.
3. If the person is conscious and can swallow, give them oral rehydration solution or diluted sports drink. Slowly.
4. If they are unconscious, cannot swallow, or aren’t responding when you speak to them, call 119 immediately. Do not wait for improvement.

Two common mistakes

Assuming heatstroke only happens outdoors. Most fatal cases in Japan happen indoors. If the room is above about 28°C, indoors offers no meaningful protection.

Assuming that alcohol or beer will help. Alcohol is a diuretic. It accelerates dehydration. In a hot environment, an evening beer is not a coolant. It’s a risk factor.

A short protocol for the summer

• Water on a schedule. 1.5 liters daily minimum in hot weather.
• Air conditioner running when the room is above 28°C. Period.
• Check the daily WBGT reading, published by the Ministry of Environment. Above 28 is caution; above 31 is danger.
• Outings early or late, not midday.
• A daily call to any elderly family member living alone.

None of this is heroic. All of it works. The Japanese summer has changed, and the response to it needs to change too. The people paying the biggest price for cultural stoicism about air conditioning are the ones this article is written for.