Four-month operational heat acclimatization positively affects the level of heat tolerance 6 months later

Heatwaves and human sleep: Stress response versus adaptation

The World Meteorological Organization considers a heatwave as "a period of statistically unusual hot weather persisting for a number of days and nights". Accompanying the ongoing global climate change, sharp heatwave bouts occur worldwide, growing in frequency and intensity, and beginning earlier in the season. Heatwaves exacerbate the risk of heat-related illnesses, hence human morbidity and mortality, particularly in vulnerable elderly and children. Heat-related illnesses present a continuum from normothermic (prickly heat, heat edema, heat cramps, heat tetany) to hyperthermic syndromes (from heat syncope and heat exhaustion to lethal heat stroke). Heat stroke may occur through passive heating and/or exertional exercise. "Normal sleep", such as observed in temperate conditions, is altered during heatwaves. Brisk excessive heat bouts shorten and fragment human sleep. Particularly, deep N3 sleep (formerly slow-wave sleep) and REM sleep are depleted, such as in other stressful situations. The resultant sleep loss is deleterious to cognitive performance, emotional brain function, behavior, and susceptibility to chronic health conditions and infectious diseases. Our group has previously demonstrated that sleep constitutes an adaptive mechanism during climatic heat acclimatization. In parallel, artificial heat acclimation procedures have been proposed in sports and military activities, and for the elderly. Other preventive actions should be considered, such as education and urban heat island cooling (vegetation, white paint), thus avoiding energy-hungry air conditioning.

Machine learning analysis and risk prediction of weather-sensitive mortality related to cardiovascular disease during summer in Tokyo, Japan

Climate-sensitive diseases developing from heat or cold stress threaten human health. Therefore, the future health risk induced by climate change and the aging of society need to be assessed. We developed a prediction model for mortality due to cardiovascular diseases such as myocardial infarction and cerebral infarction, which are weather or climate sensitive, using machine learning (ML) techniques. We evaluated the daily mortality of ischaemic heart disease (IHD) and cerebrovascular disease (CEV) in Tokyo and Osaka City, Japan, during summer. The significance of delayed effects of daily maximum temperature and other weather elements on mortality was previously demonstrated using a distributed lag nonlinear model. We conducted ML by a LightGBM algorithm that included specified lag days, with several temperature- and air pressure-related elements, to assess the respective mortality risks for IHD and CEV, based on training and test data for summer 2010-2019. These models were used to evaluate the effect of climate change on the risk for IHD mortality in Tokyo by applying transfer learning (TL). ML with TL predicted that the daily IHD mortality risk in Tokyo would averagely increase by 29% and 35% at the 95th and 99th percentiles, respectively, using a high-level warming-climate scenario in 2045-2055, compared to the risk simulated using ML in 2009-2019.

The effects of heat exposure on tropical farm workers in Malaysia: six-month physiological health monitoring

Farmers in tropical countries have been impacted by slow-onset heat stress. By comparing the nature of farming activities performed by conventional farmworkers and agroecological farmers, this study examined the changes in physiological health in responses to heat exposure through a six-month longitudinal study. Throughout the six-month follow-up period, the heat stress index (HSI), physiological strain indices (PSI), and physiological health parameters (BMI, blood glucose level, blood cholesterol level, uric acid level) were measured and repeated every two-month. Physiological parameters were recorded twice daily, before and during their first lunch break. This study found that slow-onset heat stress affects farmers differently. The health of agroecological farmers is more resistant to slow-onset extreme temperatures. Pre-existing metabolic health effects from pesticide exposure make conventional farmers more susceptible to extreme temperatures, delaying their bodies' adaptation to rising temperatures.