Heatstroke and heat-related illnesses: What are the dangers and why you can be at risk even in colder weather

SINGAPORE — With heatwaves persisting around the world from Europe to Southeast Asia, doctors are advising people to be vigilant about their health. 

Be it heat exhaustion or heatstroke, people who are vulnerable need to take extra care.

At least 30 people have died from heatstroke in Thailand this year, while two such deaths were reported in Malaysia.

Temperatures have gone above 40°C in parts of Asia and last month, it went above 50°C in Mecca, Islam’s holiest city, killing more than 1,000 pilgrims, news reports said.

In India, six students collapsed in one day in May when it was 50°C.

Although there has been no reported deaths in Singapore, one doctor said that more people are seeking emergency treatments at the hospital.

Dr Ian Mathews, senior consultant at the Emergency Medicine Department of the National University Hospital (NUH), told TODAY: “Over the last 12 months, there has been a more-than-twofold increase in heat-related illnesses such as heatstroke and heat exhaustion (seen at) our emergency department.”

There were 42 cases seen from June last year to May this year, which is more than double the 19 cases reported in the same period of the previous year. 

He said that it is reasonable to infer that the increase in heat-related cases at NUH indicates a similar trend in other hospitals in Singapore. 

Dr Mathews also believes that there is a link between the warming climate and the uptick in heat-related illnesses

Data from the Meteorological Service Singapore showed that temperatures in Singapore are rising twice as fast as the global average at 0.25°C a decade. 

The weather agency attributed the accelerated rise in temperatures for Singapore to urbanisation, since eight out of the 10 warmest years on record were in the 21st century, while all 10 warmest years took place from 1997 onwards. 

Last year was the fourth warmest year on record for Singapore. 

WHY IT MATTERS

Associate Professor Jason Lee Kai Wei said that heat stress has many indirect impacts, including:

• Heat-induced aggression
• A higher likelihood of risk-taking due to compromised decision-making
• Reduced physical activity that leads to a host of physical and mental health problems
• Increased risk of myopia (short-sightedness)

Assoc Prof Lee is the director of the Heat Resilience and Performance Centre at the Yong Loo Lin School of Medicine in the National University Singapore (NUS).

There is also increasing evidence that rising temperatures will cause air quality to worsen. 

If heat-related illnesses continue to rise, Singapore’s healthcare system, already under strain, could reach a tipping point, he added. 

Therefore, it is crucial to address this early through widespread education and preventive measures at both individual and national levels.

WHAT IS HEATSTROKE AND HEAT EXHAUSTION?

It is important to first understand the difference between heatstroke and heat exhaustion. 

Even though both have potentially severe consequences if left untreated, there are differences in their signs and how they affect the human body. 

1. Heat exhaustion

This is defined by the United States’ Centers for Disease Control and Prevention as the body’s response to an excessive loss of water and salt, usually through perspiring.

Symptoms include headache, nausea, dizziness, weakness and irritability. 

Heat exhaustion can progress to heatstroke, which happens when the body can no longer control its temperature. 

2. Heatstroke

A classic heatstroke is triggered by prolonged exposure to high heat and humidity.

An exertional heatstroke is caused by intense physical activity in hot and humid conditions. 

Either way, when it happens, the body’s temperature will rise rapidly and one may fail to expel heat through perspiration. 

When the body’s core temperature go as high as 41°C, it can trigger body-wide organ failure and loss of consciousness.

A person experiencing heatstroke may also experience an altered mental state, Dr Mathews said.

As one of the most serious heat-related illnesses, heatstroke can be life-threatening if not promptly recognised and treated. 

Lesser-known signs to look out for include nausea, vomiting, flushed skin, rapid breathing, racing heart rate, muscle cramps, and weakness.

Identifying these symptoms early is crucial in preventing a heatstroke case from escalating.

WHO ARE AT RISK OF HEATSTROKE AND HEAT-RELATED ILLNESSES

1. People engaged in physical activities

• Delivery riders, construction workers, firefighters and military personnel are vulnerable to exertional heatstroke because they have to perform strenuous tasks outdoors and in the heat for long hours
• Athletes, too, and people who work out regularly to keep fit should be mindful
• Those whose jobs involve wearing gear that restricts perspiration from evaporating, such as people working in mascot costumes and healthcare workers donning personal protective equipment

2. Infants and children

Assoc Prof Lee from NUS said that classic cases of heatstroke, which occurs after prolonged exposure to high heat and humidity, usually affect infants and the young.

Speaking on the increased risk of heatstroke in toddlers and young children, Dr Mathews from NUH explained that their smaller bodies absorb heat more quickly. 

They also perspire less than adults and do so only at higher body temperatures. 

Besides that, they may have a higher core temperature than older children and adults, making them more prone to exertional heatstroke, especially when they are playing and having prolonged physical education classes outdoors.

Adults should monitor them because young children are unable to articulate well when they are in physical distress.

3. People who are unfit and have health conditions

People with poor fitness, are obese or have diabetes, cardiovascular diseases and respiratory conditions may also be susceptible to heatstroke.

Senior citizens with chronic diseases and on a regimen of chronic disease medications should take greater care because they are at risk of non-exertional heatstroke.

At an older age, they are not as attuned to their body’s need for water due to a blunted thirst response, so they drink less water than the average active, younger adult.

When dehydrated, their bodies are more prone to respond poorly to heat stress.

And if they take certain medications, Assoc Prof Lee said that these may further hinder the body’s ability to lose heat and regulate its core temperature to optimal levels. 

Such medications include diuretics and anticholinergics, Dr Mathews said. 

Diuretics, typically prescribed to patients with heart conditions, for instance, work to remove extra fluid and salt out of the body. Anticholinergic drugs are commonly used to treat ailments such as allergies, an overactive bladder, insomnia and depression.

Those taking such medication should pay attention when they are under prolonged exposure to heat.

Another thing to note is that although the core symptoms of heatstroke are similar regardless of age, there may be subtler symptoms such as confusion and lethargy among older adults and young children.

WHAT ARE THE MISCONCEPTIONS ABOUT HEATSTROKE

A common misconception about heatstroke is that it occurs only during physical exertion, Dr Mathews said.

However, you can get a heatstroke even with light activity or at rest, especially if you are among the vulnerable groups. 

Another misconception is that drinking water alone is enough to prevent heatstroke. 

Hydration is crucial, but it must be paired with proper acclimatisation to heat (see below) and other preventive measures.

Assoc Prof Lee said that heat stress can affect the body not just through the environment, but also through one’s attire and the activity being done. 

In relation to this, he warned that people should not only be careful during the times of the year when temperatures are at their highest.

This is because the body can still heat up when one is doing physical labour or activity during cooler periods in a humid place such as Singapore.

Exertional heatstroke cases are higher during such times due to the widespread perception that it is safe to exert oneself more.

A study by researchers from the Duke-NUS Medical School analysed data from patients primarily diagnosed with heat-related illnesses from 2008 to 2020 at the emergency department of the Singapore General Hospital.

They found that cases occurred most commonly on weekends especially Sundays when people tend to take part in sporting or outdoor activities, as well as in December, which is one of the cooler months here. 

A significant number of cases in December coincided with the day of an annual year-end marathon.

WHAT TO DO IF SOMEONE IS HAVING A HEATSTROKE 

Knowing how to respond in a heatstroke emergency and what preventive measures to take can minimise severe outcomes and save lives.

Dr Mathews advised that if someone near you appears to be experiencing heatstroke:

• Immediately move the person to a cooler environment
• Remove excess clothing
• Apply cool, wet cloths to the skin or immerse the person in cool water
• If the person is conscious, giving the person some fluids is also essential
• As soon as possible, call for emergency medical help because heatstroke can escalate rapidly

Treatment for heatstroke is generally consistent across age groups, but older adults may need to be monitored more closely due to potential underlying health conditions.

WAYS TO PREVENT HEAT STRESS, AVOID A HEATSTROKE

Dr Mathews recommended:

• Avoiding strenuous activities during peak heat hours (usually lasting from 11am to 4pm)
• Wearing lightweight and light-coloured clothing

For other preventive measures:

• Hydration is obviously important
• Give yourself or people you are minding work-rest periods where needed
• Fitness conditioning and heat acclimatisation are ways to build your body's resilience to heat stress

Assoc Prof Lee emphasised the importance of keeping fit and acclimatising to the heat.

Heat acclimatisation is about improving one’s heat tolerance by gradually increasing the intensity or duration of activities done in a hot setting. 

Children, seniors and healthy adults alike can be heat-acclimatised in accordance with their bodily limits.

However, before they do so, it is important to ensure a decent level of aerobic fitness. 

This is because one needs to exercise to generate a certain amount of body heat before building heat acclimatisation. 

Assoc Prof Lee recommended engaging in more aerobic or endurance-based exercises to “heat-proof” the body.

Doing so trains the heart to pump blood more efficiently and raise one’s thermal tolerance.

You may also gradually build up a tolerance to heat by having shorter heat exposure sessions and incorporating rest and recovery between these sessions. 

“In general, it takes about two to three weeks to get fully heat-acclimated," he said.

“After that, we generally advise all to be aerobically active every other day — not more than 48 hours being sedentary is recommended — in order to maintain their heat acclimatisation status.”

Ideally, heat acclimatisation should be done in a way that is naturally sustainable.

For example, it may be tempting to switch on an air-conditioner as soon as it feels hot at home, but Assoc Prof Lee warned against overcooling a room and suggested turning on the fan and keeping one’s home ventilated instead.

“People can hide in an air-conditioning environment for a while, but it is also good to allow the body to physiologically acclimatise to the rising temperatures so that the body can work to combat and dispel heat more effectively.”