Climatic influences on cardiovascular diseases

Table 1 Main studies on the relations between weather and general mortality

Ref.	Setting and population	Year	Main results
Chung et al[11]	Fifteen cities in Northeast Asia	1972-2010	Cold effects had longer time lags (5–11 d) than heat effects, which were immediate (1–3 d). Both cold and heat effects were more significant for cardiorespiratory mortality than for other causes of death
Curriero et al[4]	Eleven large eastern United States cities	1973-1994	Current and recent days' temperatures were the weather components most strongly predictive of mortality. Mortality risk generally decreased as temperature increased from the coldest days to a certain threshold temperature, which varied by latitude, above which mortality risk increased as temperature increased. Strong association of the temperature-mortality relation with latitude, with a greater effect of colder temperatures on mortality risk in more-southern cities and of warmer temperatures in more-northern cities
Fernández-Raga et al[18]	Castile-Leòn, Spain	1980-1988	Temperatures with lower death risk for patients with cardiovascular diseases (16.8°C) are apparently lower than those for patients with respiratory diseases (18.1°C)
Achebak et al[31]	47 major cities in Spain	1980-2015	Reduction in relative risks of cause-specific and cause-sex mortality across the whole range of summer temperatures
Gemmel et al[2]	Scotland, United Kingdom	1981-1993	A 1°C decrease in mean temperature was associated with a 1% increase in deaths 1 wk later
Guo et al[15]	400 communities from 18 countries/regions	1984-2013	Heat waves had significant cumulative associations with mortality but varied by community. The higher the temperature threshold used to define heat waves, the higher heat wave associations on mortality. The association between heat waves and mortality appeared acutely and lasted for 3 and 4 d. Heat waves had higher associations with mortality in moderate areas than in cold and hot areas
Gasparrini et al[22]	305 locations in 9 countries: Australia, Canada, China, Italy, Japan, South Korea, Spain, United Kingdom, and United States	1985-2012	Strong evidence of a reduction in risk over the season. Relative risks for the 99th percentile versus the minimum mortality temperature were in the range of 1.15–2.03 in early summer. In late summer, the excess was substantially reduced or abated, with relative risks in the range of 0.97–1.41
Gasparrini et al[27]	384 locations in Australia, Brazil, Canada, China, Italy, Japan, South Korea, Spain, Sweden, Taiwan, Thailand, United Kingdom, and United States	1985-2012	7.71% (95%CI: 7.43–7.91) of mortality was attributable to non-optimum temperature in the selected countries within the study period, with substantial differences between countries, ranging from 3.37% (3.06 to 3.63) in Thailand to 11.00% (9.29 to 12.47) in China. The temperature percentile of minimum mortality varied from roughly the 60th percentile in tropical areas to about the 80–90th percentile in temperate regions
Aylin et al[5]	Great Britain	1986-1996	Significant association between mortality and temperature with 1.5 higher odds of dying for every 1°C reduction in winter temperature
The Eurowinter Group[1]	Men and women aged 50–59 and 65–74 in north Finland, south Finland, Baden-Württemburg, the Netherlands, London, and north Italy	1988-1992	Percentage increases in all-cause mortality per 1°C fall in temperature below 18°C were greater in warmer regions than in colder regions. High indices of cold-related mortality were associated with high mean winter temperatures (P < 0.01 for all-cause mortality and respiratory mortality; P > 0.05 for mortality from ischaemic heart disease and cerebrovascular disease)
Rocklöv et al[30]	Stockholm, Sweden	1990-2002	A high rate of respiratory and cardiovascular mortality in winter reduced the heat effect the following summer. The cumulative effect per 1°C increase was 0.95% below and 0.89% above a threshold (21.3°C) after a winter with low cardiovascular and respiratory mortality, but -0.23% below and 0.21% above the threshold after a winter with high cardiovascular and respiratory mortality
Ragettli et al[32]	Switzerland	1995-2013	Significant temperature-mortality relationships were found for maximal (1.15; 1.08–1.22); mean (1.16; 1.09–1.23), and minimal (1.23; 1.15–1.32) temperature. Mortality risks were higher at the beginning of the summer. Recent non-significant reduction in the effect of high temperatures on mortality
Chen et al[10]	All deaths among residents in Ontario, Canada	1996-2010	In warm seasons, each 5°C increase in daily mean temperature was associated with a 2.5% increase in nonaccidental deaths (95%CI: 1.3%-3.8%) on the day of exposure (lag 0). In cold seasons, each 5°C decrease in daily temperature was associated with a 3.0% (95%CI: 1.8%-4.2%) increase in nonaccidental deaths, which persisted over 7 d. Cold-related effects were stronger for cardiovascular-related deaths (any cardiovascular death: 4.1%, 95%CI: 2.3%-5.9%; CHD: 5.8%, 95%CI: 3.6%-8.1%). Each 5°C change in daily temperature was estimated to induce 7 excess deaths per day in cold seasons and 4 excess deaths in warm seasons
Oudin Åström et al[24]	Eastern Esthonia	1997-2013	Immediate increase in mortality associated with temperatures exceeding the 75th percentile of summer maximum temperatures, corresponding to approximately 23°C. This increase lasted for a couple of days
Bell et al[21]	Mexico City, Mexico; Sao Paulo, Brazil; Santiago, Chile	1998-2002	Elevated temperatures (in particular same and previous day apparent temperature) are associated with mortality risk
Chan et al[12]	Hong Kong, China	1998-2006	An average 18°C increase in daily mean temperature above 28.2°C was associated with a 1.8% increase in mortality. Non-cancer related causes such as cardiovascular and respiratory infection-related deaths were more sensitive to high temperature
Xu et al[34]	Barcelona, Spain	1999-2006	The effect of three consecutive hot days was a 30% increase in all-cause mortality (RR = 1.30, 95%CI: 1.24-1.38)
Guo et al[23]	Chiang Mai city, Thailand	1999-2008	Both hot and cold temperatures resulted in immediate increase in all mortality types and age groups. Generally, the hot effects on all mortality types and age groups were short-term, while the cold effects lasted longer. The relative risk of mortality associated with cold temperature (19.35°C, 1st centile) relative to 24.7°C (25th centile) was 1.29 (95%CI: 1.16, 1.44) for lags 0–21. The relative risk of mortality associated with high temperature (31.7°C, 99th centile) relative to 28°C (75th centile) was 1.11 (95%CI: 1.00, 1.24) for lags 0–21
Oudin Åström et al[24]	Population over 50 years in Rome, Italy, and Stockholm, Sweden	2000-2008	The percent increase in daily mortality during heat waves as compared to normal summer days was 22% (95%CI: 18%-26%) in Rome and 8% (95%CI: 3%-12%) in Stockholm
Zafeiratou et al[8]	42 Municipalities within the Greater Athens Area, Greece	2000-2012	Significant effects of daily temperature increase on all-cause, cardiovascular, and respiratory mortality (e.g., for all ages 4.16% (95%CI: 3.73%, 4.60%) per 1 C increase in daily temperature (lags 0–3)
Fu et al[14]	India	2001–2013	Mortality from all medical causes, stroke, and respiratory diseases showed excess risks at moderately cold temperature and hot temperature. Moderately cold temperature was estimated to have higher attributable risks [6.3% (95% empirical CI 1.1 to 11.1) for all medical deaths, 27.2% (11.4 to 40.2) for stroke, 9.7% (3.7 to 15.3) for IHD, and 6.5% (3.5 to 9.2) for respiratory diseases] than extremely cold, moderately hot, and extremely hot temperatures
Zeng et al[9]	15973 elderly residents of 866 counties and cities, China	2002-2005	Low seasonal temperatures increase the odds of mortality
Argaud et al[25]	Lyon, France	2003	Independent contribution to mortality from heatstroke if patients used long-term antihypertensive medication (HR, 2.17; 95%CI: 1.17-4.05), or presented at admission with cardiovascular failure (HR, 2.43; 95%CI: 1.14-5.17)
Zhang et al[35]	Wuhan, China	2003-2006	U-shaped relationship between temperature and mortality. Cold effect was delayed, whereas hot effect was acute, both of which lasted for several days. For cold effects over lag 0–21 d, a 1°C decrease in mean temperature below cold thresholds was associated with a 2.39% (95%CI: 1.71, 3.08) increase in non-accidental mortality, 3.65% (95%CI: 2.62, 4.69) increase in cardiovascular mortality, 3.87% (95%CI: 1.57, 6.22) increase in respiratory mortality, 3.13% (95%CI: 1.88, 4.38) increase in stroke mortality, and 21.57% (95%CI: 12.59, 31.26) increase in CHD mortality. For hot effects over lag 0–7 d, a 1 °C increase in mean temperature above the hot thresholds was associated with a 25.18% (95%CI: 18.74, 31.96) increase in non-accidental mortality, 34.10% (95%CI: 25.63, 43.16) increase in cardiovascular mortality, 24.27% (95%CI: 7.55, 43.59) increase in respiratory mortality, 59.1% (95%CI: 41.81, 78.5) increase in stroke mortality, and 17.00% (95%CI: 7.91, 26.87) increase in CHD mortality
Gómez-Acebo et al[7]	Cantabria (northern Spain)	2003-2006	Raising maximum or minimum temperatures by 1ºC was associated with a 2% excess in mortality risk throughout the warm period. No effect in mortality on the cold season
Gómez-Acebo et al[17]	Cantabria (northern Spain)	2004-2005	The higher OR for cancer mortality was seen on the first day of exposure (OR = 4.91; 95%CI: 1.65–13.07 in the whole population). Cardiovascular (OR = 2.63; 95%CI: 1.88–3.67) and respiratory mortality (OR = 2.72; 95%CI: 1.46–5.08) showed a weaker effect
Analitis et al[26]	9 European cities	2004-2010	In the warm season, the percentage increase in all deaths from natural causes per ◦C increase in ambient temperature tended to be greater during high ozone days. For the cold period, no evidence for synergy was found.
McMichael et al[19]	Urban populations in Delhi, Monterrey, Mexico City, Chiang Mai, Bangkok, Salvador, Sao Paulo, Santiago, Cape Town, Ljubljana, Bucharest and Sofia.	2007	Most cities showed a U-shaped temperature-mortality relationship, with clear evidence of increasing death rates at colder temperatures and with increasing heat. Heat thresholds were generally higher in cities with warmer climates, while cold thresholds were unrelated to climate
Rabczenko et al[20]	Warsaw, Poland	2008-2013	Analysis of dependence between temperature and mortality for whole population as well as for subpopulations with respect to sex and age demonstrated its similar U-shape. Comfort varied between 20 and 24°C, with slight tendency to be higher for woman
Can et al[13]	Istanbul, Turkey	2013-2017	Three extreme heat waves in summer months of 2015, 2016, and 2017, which covered 14 days in total, significantly increased the mortality rate and caused 419 excess deaths in 23 d of exposure
Oray et al[16]	Izmir province, Turkey	2016	During the study period, the mean number of ED visits and mortality rates were significantly higher than the previous year's same period [320 ± 30/d vs 269 ± 27/d, (P < 0.01), and 1.6% vs 0.7%, (P < 0.01)]. Although the admission rate was similar between the study period and the other 21 d of June 2016 [320 ± 30/d vs 310 ± 32/d, (P = 0.445)] in-hospital mortality rate was significantly higher [1.6% vs 0.7%, (P < 0.01)]

CHD: Coronary heart disease; CI: Confidence interval; OR: Odds ratio.