The heatwave plan for England says those at high risk include people over 75, babies, young children, people with serious physical or mental illnesses and women. The paper does not explain why women are included in the list, but the UK’s Health Security Agency pointed to a study in the Netherlands that looked at mortality after various heatwaves and found that older women are at higher risk than men. The researchers said the results were not just about age. “When equal ages were taken into account, mortality rates were still 15% higher for women,” the team wrote about their analysis of data from the 2003 heatwave in France. Another study by Dutch and German researchers, looking at 23 years of temperature data from the Netherlands along with daily mortality data, also found gender differences. “Heat-related mortality was higher in women than in men, especially in the older age group (≥ 80 years) under extreme heat,” they said. The team said the findings do not appear to be because older people are more vulnerable to heat and women generally live longer than men. Hein Daanen, professor of exercise physiology at VU University Amsterdam and an author of the study, said the team speculated that reduced sweat production in women may play a role. “Rough, old man [people] they sweat half as much as young men and women half as much as men,” he said. In other words, the study notes, “the ability of older females to lose body heat is the lowest.” The team said stress placed on the cardiovascular system by heat may also be involved. “Cardiovascular strain is reportedly higher in women, possibly explaining the higher risk of mortality in the heat,” they wrote. Among other possibilities, the team notes that older women may be at increased risk because they may be more likely to live alone — a known risk factor in hot weather — and may be less active overall than men, but more likely to be active in the household. “Continuing these activities during hot weather when they are less physically fit puts women at greater risk of overheating and cardiovascular stress than men,” the team wrote. Ollie Jay, a professor of heat and health at the University of Sydney, also noted that studies had shown that peak sweat rates in young healthy women tended to be lower than their male counterparts. “If this is why there are more women in the mortality and morbidity data in the heatwaves, we don’t really know yet. It is also unclear whether there is any interaction of this gender effect with age,” he said. Mike Tipton, professor of human and applied physiology at the University of Portsmouth, said women may be more at risk of heatstroke because they have higher core temperatures after ovulation, while they are often smaller than men and therefore have more surface area in mass. ratio, meaning they heat up faster. But Jay said: “The most likely answer is that it’s a combination of factors and we need to do more research to understand what’s going on.”
