The interplay between climate change and ageing: A systematic review of health indicators

Interestingly, one main report of the selected articles is that forms of ambient temperature variability have a very strong effect on health outcomes. For example, findings from an exami- nation of the relation between seasonal temperature variability and emergency hospital admis- sions for respiratory diseases reported an HR of 1.20 (95% CI 1.08–1.32) for total incident respiratory diseases, 1.15 (95% CI 1.01–1.31) for pneumonia and 1.41 (95% CI 1.15–1.71) for COPD per 1˚C change in wintertime temperature variability [49]. This is particularly interest- ing because climate changes imply not only the increase of average ambient temperatures, but the frequency of extreme temperatures but also the variability of temperature within days, sea- sons, and years. In fact, Shi et al. found that a 1˚C increase in summer and winter mean tem- perature corresponded to an increase of 2.46% (95% CI: 2.33–2.59) and 1.46% (95% CI: 1.42– 1.50) in the death rate, respectively. On the other hand, a 1˚C increase in temperature variabil- ity yielded a 3.71% (95% CI: 3.21–4.22) and 0.59% (95% CI: 0.37–0.81) increase in annual deaths in summer and winter, respectively [48]. Also, it is important to highlight that non-optimum temperatures, both high and low, con- tributed to an increased risk of all-cause mortality [40, 42, 45, 48]. A study in Bulgaria between 2000 and 2017 reported that 12.3% (95% CI: 7.3–16.8) of deaths in that period were due to non-optimum temperatures. The temperature-attributable mortality was from moderate cold

(10.9%; 95% CI: 5.8–15.6), followed by moderate heat (1.1%; 95% CI: 0.5–1.6), extreme cold (0.6%; 0.4–0.7) and extreme heat (0.3%; 95% CI: 0.1–0.4) [45]. Furthermore, the majority of the selected articles analysed individual covariates or possible effect modifiers on morbidity or mortality. The most common included were gender, socio- economic status, and education level. Depending on the climate change phenomenon and health outcome studied, females presented a higher or a lower risk compared to men. For example, in contrast to men, in the findings of Shi et al., women were more sensitive to increased summer mean temperature but less to increased season temperature variability [48]. Contrarily, a low socioeconomic status was frequently associated with a higher health risk. A low individual socioeconomic status or poverty was correlated with an increased risk of dementia hospitalization related to a higher mean winter temperature and increased tempera- ture variability [10]. The effect of ENSO in increasing mortality risk was also higher in families who had a low income per capita [52]. In the same way, a low education level was associated with the aggravation of health outcomes. For instance, the relative risk of respiratory admis- sions on smoke-wave days compared with non-smoke-wave days was higher for people living in areas with less educated individuals (RR = 1.13, 95% CI: 0,97–1.31) comparing to those liv- ing in areas with higher educated individuals (RR = 1.06, 95% CI:0.98–1.14) [43].

Importantly, effect modification by different age subpopulations among older adults was also frequently considered. The most relevant findings were the following. Younger age groups (65–74 and 75–84 vs >84) were at higher risk for hospitalization due to dementia relating to a higher mean winter temperature or increased temperature variations [10]. Individuals aged 78 years or older had an increased risk of renal/heat/respiratory hospitalizations 6 days following extreme heat compared to individuals aged 65–77 years, 15% (95% CI: 11–19) and 7% (95% CI: 4–10), respectively [41]. Individuals aged 75 or over showed a higher all-cause mortality risk to changes in 1˚C in seasonal mean temperature [48]. Finally, individuals aged 85 and over, compared to the 65–84 age group, had a greater burden of temperature-related mortality due to cold or hot temperatures [45]. Discussion Although the impact of climate change on human health is widely acknowledged, it remains difficult to attribute morbidity and mortality to the changing climate. Nevertheless, we showed PLOS ONE Climate change, ageing and health PLOS ONE | https://doi.org/10.1371/journal.pone.0297116 April 24, 2024 11 / 17