SINGAPORE - People who are more vulnerable to heat stress may face greater challenges as climate change nudges up temperatures in Singapore.

This is where researchers believe a personalised heat advisory will help.

With it, such people will be able to better regulate their time spent doing physical activities outdoors, and avoid heat-related risks such as loss of muscular strength and even heat stroke.

The advisory is one of the aims of a study led by Associate Professor Jason Lee from the Human Potential Translational Research Programme at the National University of Singapore's Yong Loo Lin School of Medicine.

The study will look to establish the thresholds for the vulnerable groups to determine how well they will cope in Singapore's current weather and in scenarios of temperature rise due to global warming.

Prof Lee said: "Excessive heat strain - caused by prolonged activities outdoors - could lead to greater health risks, especially for certain groups of people."

The risks include cognitive impairment, or poorer decision-making abilities, and reduced cardiovascular endurance, making the heart work harder.

In some severe cases, individuals may be at risk of heat stroke, which may lead to damage to one's brains, heart and kidneys.

The study, which is part of the Cooling Singapore project, a research initiative funded by the National Research Foundation, will focus on three vulnerable groups:

- Primary school pupils.

- Adults not acclimatised to Singapore's hot and humid weather, for example, tourists and those leading long-term sedentary lifestyles.

- Those aged 65 and above.

For children, it may be a case of enabling parents to feel confident about their kids going out to play.

Prof Lee said: "Parents... may be overprotective of their children and could be unwilling to let them play outside if they perceive the weather to be too hot.

"But if we could establish the child's thresholds under different climatic conditions, children could then play outdoors safely, say within a stipulated timeframe, while averting possible heat stress."

He noted that children's heat tolerance could have been reduced, as they are now spending a lot less time playing and exercising outdoors compared with before.

In addition, childhood obesity is on the rise - and is often related to poor heat tolerance.

The study will be conducted in a lab setting, with environmental conditions mimicking current and projected temperatures in Singapore.

In order to ensure that these simulated conditions are as realistic as possible, the amount of heat stress an individual may face in direct sunlight will be taken into account.

This is known as wet bulb globe temperature, which measures dry temperatures, humidity, wind speed, and the amount of cloud cover, which influences solar radiation.

Participants will then be asked to do a series of exercises under a range of climatic conditions, where data such as their body temperature, gait and cognitive functions will be gathered and studied carefully.

As different segments of the population tolerate and experience heat differently, the data from the study will be used to derive a personalised heat-health index that incorporates an individual's physical health with real-time climate conditions to identify their thresholds.

This would help them avert the possibility of excessive heat strain.

"At current temperatures, one's physiological threshold may be reached after a 30-minute run, for example. But at a hotter, more humid temperature, the same threshold may have been reached after a 20-minute run. Such information can help people shape their behaviour accordingly as Singapore becomes hotter over time," said Prof Lee.

The advisory will also include some precautions that individuals should take, such as more frequent rest during workouts, or cooling interventions such as cold showers.

The three-year study, which started on Oct 1, will involve about 120 participants.

Once the thresholds for these vulnerable groups have been established, future research work will look at the physiological thresholds for those with diseases such as diabetes and cardiovascular disease, and individuals with disabilities.

For instance, those with spinal cord injuries are known to have their ability to regulate heat affected, due to damaged connections between the body and the brain, Prof Lee said.

Eventually, he hopes to develop an app that would give prescriptive and personalised heat-health advisories targeting different segments of the population.

He said: "This app could be especially useful during the transition months - from rainy or cooler weather to hotter, sunnier weather, where people would need to adapt and make adjustments to their exercise regime, for example."

An algorithm could also be developed, taking into account climatic conditions, clothing and one's physical health, he added.

"Having such feedback could improve the accuracy of our heat-health advisory to both prevent excessive heat exposure and encourage outdoor physical activities at a personalised level," he said.