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Heat stress in the summer in Israel increases the risk of stroke, especially a week after its occurrence

"Previous studies have shown a connection between temperature and the occurrence of various diseases. In a stroke, apparently, the heat causes a low fluid balance which leads to changes in the brain including dilation of blood vessels, a decrease in blood volume and an increase in the risk of clots. This usually happens to those who are also in a risk group," the researchers explain

The climate crisis: if we are all to blame - then none of us is to blame. Image: depositphotos.com
The climate crisis: if we are all to blame - then none of us is to blame. Image: depositphotos.com

The effects of the climate crisis on public health are many and varied. Among climate changes, extreme heat is apparently the most significant cause of the increase in morbidity and mortality. A study conducted at the School of Public Health and the School of Environmental Sciences at the University of Haifa, which combines climate, health and policy, found a link between summer weather and stroke. The research was carried out by the researchers Prof. Galit Weinstein (epidemiologist who deals with cognitive and brain diseases), Prof. Mia Negev (researcher of health, environment and climate resilience), Prof. Shlomit Paz (climatologist, researcher of climate change and its effects), Shiraz Vared (doctoral student) and Thilah Yoeli (Masternative).

Stroke is a major cause of morbidity and mortality in old age. It is usually caused by the blockage of a cerebral blood vessel by a blood clot or embolism and disruption of the blood supply to the brain. Thus the damaged brain area, the one that suffers from a lack of blood and oxygen, loses its functional capabilities, and thus the function of the organs it controls may be affected.

What is the question? Does high temperature increase the risk of stroke?

"Previous studies have shown a connection between temperature and the occurrence of various diseases. In a stroke, apparently, the heat causes a low fluid balance which leads to changes in the brain including dilation of blood vessels, a decrease in blood volume and an increase in the risk of clots. This usually happens to those who are also in a risk group," explains Prof. Weinstein.

In their study, which won a research grant from the National Science Foundation, the researchers sought to examine the relationship between ambient temperature, humidity and heat load and the risk of stroke during the summer season in Israel. They also checked whether these relationships change in relation to socio-demographic characteristics and background morbidity.

The researchers used data on stroke cases from 2014 to 2019 from the Ministry of Health's National Stroke Registry. A total of 31,000 stroke cases were recorded over six summer seasons (early June to late September) over five years. These data were merged with climate conditions data collected through a meteorological satellite for that period by Prof. Itai Kellogg from the Department of Environmental Sciences, Geoinformatics and Urban Planning at Ben Gurion University. The climate data included temperature, humidity and the interaction between them (for the purpose of defining the degree of heat load) and were measured for each square kilometer in Israel. These data were cross-referenced with the residential addresses where the stroke cases occurred. In this way it was possible to assess the degree of morbidity in each area with high resolution.

"The temperature of the day of the stroke was compared to the temperature of the other days (for example if the stroke occurred on a Wednesday, the temperature of that day was compared to that of every other Wednesday in the same month and year). In this way, we effectively neutralized all the other risk factors for stroke, such as blood pressure, diabetes, smoking, inactivity and exposure to air pollution, and we were only left with the relationship between heat stress and the risk of stroke," explains Prof. Weinstein.

It was found that each of the tested climate indicators was positively and significantly related to the risk of stroke, independently of the other variables. Thus, among other things, it was found that each additional degree increased the risk of stroke by 15%. It should be noted that the strongest relationship between temperature, humidity and heat load and the risk of stroke was found when these indices were measured a week before the stroke; Moderate heat stress was associated with a 20% higher risk of stroke after one week and extreme heat stress was associated with a 23% higher risk of stroke after one week, compared to days when there was no heat stress. "It may be so because the pathological process in the brain caused by the heat load lasts for several days until the stroke occurs. In other words, there may be a window of time of about a week that allows for an intervention that will help prevent the stroke," Prof. Weinstein notes. It was also discovered that the relationship between heat stress and the occurrence of stroke was similar in socio-demographic strata and in different background diseases.

In the qualitative part of the study, which included focus groups of people at risk (aged 65 and over), it was found that they are almost unaware of the health risk inherent in climate change, of stroke symptoms and the need to go to the hospital when they appear.

It turns out that most of the people at risk are almost unaware of the health risk inherent in climate change, the symptoms of a stroke and the need to go to the hospital when they appear.

As part of the study, the researchers also held an expert workshop in collaboration with decision makers from the Ministry of Health to promote a policy to reduce the risk of stroke in the summer. The workshop presented the research findings and policy tools that exist in the world to reduce exposure to extreme heat, including: raising awareness among vulnerable populations about the risks associated with extreme heat and providing tools for self-defense (such as information transfer and workshops), opening air-conditioned cooling centers such as libraries and community centers to the general public (especially in areas where multiple elderly residents and populations living in poverty), home visits and support services for lonely, vulnerable, and chronically ill elderly by professionals or volunteers, urban planning and infrastructure improvement (expansion of shaded areas, tree planting and appropriate construction), training for health professionals, and ongoing research and monitoring On the effect of extreme heat on the elderly population.

"In the health system in Israel, there is almost no policy that deals with preparing for climate change and extreme heat waves, and it is desirable to learn how other countries (such as England and Italy) implement it and thus reduce excess morbidity and mortality," concludes Prof. Negev.

Life itself:

Prof. Galit Weinstein, married + three daughters, lives in Ramat Yishai. She likes to engage in research and publish articles and in her spare time she enjoys reading books, learning Arabic and exercising. Mia Negev

Prof. Mia Negev, married + two, lives in Kfar Saba. Loves working in academia ("I fell in love with academic research at the Arava Institute for Environmental Studies") and combining research, teaching and guiding students. In her free time she enjoys spending time with her family, hiking, going to the beach, reading books, learning Arabic, swimming, running and doing yoga. Shlomit Paz

Prof. Shlomit Paz, married + four, lives in the settlement of Hosheya in the Lower Galilee. She has been researching the climate crisis and its effects for many years. Engaged in basic and applied research and loves to teach and guide students. In her spare time she enjoys nature walks, reading and swimming.

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