Date Published: July 17, 2018
Publisher: Public Library of Science
Author(s): Holly Ching Yu Lam, Juliana Chung Ngor Chan, Andrea On Yan Luk, Emily Ying Yang Chan, William Bernard Goggins, Madeleine Thomson
Abstract: BackgroundAcute myocardial infarction (AMI) is the leading cause of death among people with diabetes mellitus (DM) and has been found to occur more frequently with extreme temperatures. With the increasing prevalence of DM and the rising global mean temperature, the number of heat-related AMI cases among DM patients may increase. This study compares excess risk of AMI during periods of extreme temperatures between patients with DM and without DM.MethodsDistributed lag nonlinear models (DLNMs) were used to estimate the short-term association between daily mean temperature and AMI admissions (International Classification of Diseases 9th revision [ICD-9] code: 410.00–410.99), stratified by DM status (ICD-9: 250.00–250.99), to all public hospitals in Hong Kong from 2002 to 2011, adjusting for other meteorological variables and air pollutants. Analyses were also stratified by season, age group, gender, and admission type (first admissions and readmissions). The admissions data and meteorological data were obtained from the Hong Kong Hospital Authority (HA) and the Hong Kong Observatory (HKO).FindingsA total of 53,769 AMI admissions were included in the study. AMI admissions among DM patients were linearly and negatively associated with temperature in the cold season (cumulative relative risk [cumRR] [95% confidence interval] in lag 0–22 days (12 °C versus 24 °C) = 2.10 [1.62–2.72]), while those among patients without DM only started increasing when temperatures dropped below 22 °C with a weaker association (cumRR = 1.43 [1.21–1.69]). In the hot season, AMI hospitalizations among DM patients started increasing when the temperature dropped below or rose above 28.8 °C (cumRR in lag 0–4 days [30.4 versus 28.8 °C] = 1.14 [1.00–1.31]), while those among patients without DM showed no association with temperature. The differences in sensitivity to temperature between patients with DM and without DM were most apparent in the group <75 years old and among first-admission cases in the cold season. The main limitation of this study was the unavailability of data on individual exposure to ambient temperature.ConclusionsDM patients had a higher increased risk of AMI admissions than non-DM patients during extreme temperatures. AMI admissions risks among DM patients rise sharply in both high and low temperatures, with a stronger effect in low temperatures, while AMI risk among non-DM patients only increased mildly in low temperatures. Targeted health protection guidelines should be provided to warn DM patients and physicians about the dangers of extreme temperatures. Further studies to project the impacts of AMI risks on DM patients by climate change are warranted.
Partial Text: Extreme ambient temperature has been reported to be associated with adverse health outcomes worldwide  and has also been linked to worsening of diabetes mellitus (DM) conditions and increased mortality [2–8]. A worldwide meta-regression study found a positive association between glucose intolerance and outdoor temperature . Studies from the United States [2–4] and Sydney, Australia  found positive associations between temperature and DM-related complications and mortality, while studies from the Philippines  and China [7,8] found increased DM mortality at both high and low temperatures. Climate change, which is leading to higher average global temperatures , and the rising prevalence of DM have been suggested to pose a “dual threat” in increasing the disease burden .
While AMI admissions in Hong Kong increased when temperatures dropped in the cold season for both DM and non-DM patients, admissions among DM patients showed a higher temperature threshold and a significantly stronger association with temperature in the cold season. In the hot season, the number of AMI admissions among DM patients increased significantly with rising temperatures above 28.8 °C, but no increased risk with high temperatures was seen for the non-DM group. The increased relative risk for DM patients with lower temperatures was higher than for the non-DM group for all subgroups. The greater sensitivity to low temperature for DM patients was more apparent in the group below 75 years old, males, and first-admission cases. In the hot season, no obvious increased relative risk was observed among non-DM patients in all subgroups at high temperatures. DM patients demonstrated higher relative risks than non-DM patients in most of the subgroups. Patients <75 showed statistically significantly different sensitivities to high temperatures between the DM and non-DM groups in the hot season, with a higher increased relative risk for the DM group. Our study found that AMI admissions increased more sharply for DM patients relative to non-DM patients during extreme temperatures, with between-group differences being particularly strong for low-temperature associations. The results showed robust association of increased risk of AMI hospitalizations among DM patients at low temperatures in both seasons and high temperatures in the hot season. By contrast, we only found mildly increased risk among non-DM patients at low temperatures, and no increase at high temperatures. The difference in sensitivity of admission numbers to temperature between DM and non-DM patients were more obvious for patients younger than 75 years old. Findings of this study should be taken into account when drafting targeted health policy against extreme temperatures and planning patient care for people with diabetes. Further studies from regions with differing climates examining effect modification of AMI–temperature associations by DM status are needed. Future studies projecting the possible effects of rising temperatures on AMI incidence among DM patients should be considered. Source: http://doi.org/10.1371/journal.pmed.1002612