Study finds nighttime heat significantly increases risk of stroke

In a recent study conducted by scientists from Helmholtz Munich and the University Hospital Augsburg, led by Dr. Alexandra Schneider, it was shown that night heat significantly increases the risk of stroke. These results could help develop preventive measures that will help the population better protect themselves from the risks associated with climate change and increasingly frequent hot nights. Additionally, knowledge of the effects of hot nights may improve patient care.

“We wanted to understand the extent to which high night temperatures pose a health risk,” says the head of the environmental risk working group at Helmholtz Munich. "This is important because climate change is causing nighttime temperatures to rise much faster than daytime temperatures."

Data on 11,000 strokes over 15 years

In their study, published in the European Heart Journal, the researchers analyzed data from the University Hospital of Augsburg. Her neurology department collected data on about 11,000 strokes over 15 years. Analysis shows that extreme heat at night increases the risk of stroke by 7%.

"Older people and women are at particular risk, and these are mostly mild strokes diagnosed in clinics after hot nights," said study lead author Dr Cheng He. "Our results clearly show that adjustments to urban planning and public health systems are critical to reducing the risks associated with rising nighttime temperatures."

“We were able to show that the risk of stroke associated with high night temperatures increased significantly between 2013 and 2020 compared to the period from 2006 to 2012,” emphasizes Professor Michael Erl, head of the Stroke Department and the Working Group on neurovascular research at the University Hospital Augsburg. From 2006 to 2012, hot nights resulted in two additional strokes per year in the study area; from 2013 to 2020, 33 additional cases were reported per year.

Recommendations for adaptation strategies and urban planning

The researchers plan to make their findings applicable in practical settings. To this end, they are working on recommendations for adaptation strategies for the public and urban planning, such as reducing the intensity of urban heat islands. The goal is to better protect the population from the effects of heat at night.

The study will also serve as a basis for further research to develop targeted preventive measures against factors that contribute to stroke. "The sooner these preventative measures are implemented, the better," says Schneider.

The study results also have important implications for hospitals. They will be able to better adapt to the incidence of strokes in the future: if the weather forecast predicts a hot night, we can expect more stroke patients to arrive at clinics. This allows clinics to plan in advance for increased staffing to care for patients, explains Professor Markus Naumann, director of the Neurological University Hospital in Augsburg.

Background: What are tropical nights?

Tropical nights are defined using the so-called Hot Nights Excess Index (HNE). It measures how much the temperature rises above a certain threshold at night. The threshold is the temperature that is exceeded on only the warmest 5% of nights over the entire study period.

In this study, this value is 14.6°C. If the temperature at night rises above this value, it is classified as a tropical night. The HNE index adds up how many degrees the temperature exceeds this threshold during the night hours to determine the intensity of the heat.