Temperatures along the East Coast began fluctuating wildly last month, from winter-like cold one day — which is normal for February — to summer-like hot the next day — which is anything but. This is a portentous harbinger of global climate change, and an irksome turn of events, as it forced people to switch their clothes, thermostats and ceiling fans from one day to another.
As it turns out, such abrupt temperature swings also may be bad for your health. Cardiology researchers in Michigan recently linked extreme day-to-day changes in temperatures to a significant increase in heart attacks, a finding that raises the disturbing possibility of yet another harmful effect of our warming planet on human health.
“Global warming is expected to cause extreme weather events, which may, in turn, result in large day-to-day fluctuations in temperature,” said Hedvig Andersson, a cardiology researcher at the University of Michigan. “Our study suggests that such fluctuations in outdoor temperature could potentially lead to an increased number of heart attacks and affect global cardiac health in the future.”
Many harmful health effects of climate change are well established, ranging from the worsening of seasonal allergies and the spread of infectious diseases, to the deadly impact of heat waves, floods and drought, among others.
Existing evidence also suggests that climate change already is tied to heart problems, from the dangerous effects of air pollution, including from climate-fueled wildfires, to that of stress, a known risk factor for heart disease. In 2016, for example, New Orleans cardiology researchers reported a three-fold rise in heart attacks in the years after Hurricane Katrina struck, likely due to the stress-induced struggles that many residents endured relocating and rebuilding in the aftermath of the storm.
The Michigan scientists, who reported their findings during a recent meeting of the American College of Cardiology, noted there is a large body of scientific evidence showing the detrimental effects of outdoor temperatures on the rate of heart attacks, including high humidity, as well as extreme heat and cold, with cold weather bringing the highest risk. But most of the earlier research has focused on overall daily temperatures. This new study is among the first to look at the relationship between heart attacks and sudden temperature deviations.
Along with overall heating, climate change is expected to produce more extreme weather events, heat waves and cold snaps, depending on where people live. There is some evidence that climate change — and Arctic warming in particular — may be leading to a more meandering jet stream, which is producing greater extremes in heat, rainfall, drought, etc. in mid-latitude regions like the United States, one reason parts of the nation are experiencing such dramatic temperature swings at odd and unexpected times.
“While the body has effective systems for responding to changes in temperature, it might be that more rapid and extreme fluctuations create more stress on those systems, which could contribute to health problems,” Andersson said, adding that scientists still don’t know the precise underlying mechanism that may be at work.
Hitinder Gurm, professor of medicine and associate chief clinical officer at Michigan Medicine — another of the researchers involved in the study — stressed that their findings don’t necessarily prove that sudden temperature fluctuations are the cause of more heart attacks, and people should continue to focus on other contributing risk factors, such as smoking, hypertension and high cholesterol.
“We know that smoking, diabetes, high cholesterol, obesity and lack of exercise are strongly associated with heart disease, and they are modifiable,” he said. “People should focus on these because we know that changing them can make a difference. Currently the best thing a person can do is take care of these. Those are way more important than worrying about temperatures. However, with expected changes in global climate and weather patterns, this is something we need to study because it’s not only the future, but is happening today, and could become an important public health issue.”
The research is based on data from more than 30,000 patients who were treated at 45 Michigan hospitals between 2010 and 2016. All of them had undergone percutaneous coronary intervention, a procedure used to open clogged arteries, after being diagnosed with ST-elevated myocardial infarction, the most serious form of heart attack.
The researchers calculated the temperature fluctuation preceding each heart attack based on weather records for the hospital’s ZIP code, defining daily temperature fluctuation as the difference between the highest and lowest recorded on the day of the heart attack.
Overall, the results showed the risk of a heart attack increased by about 5 percent for every five-degree Celsius jump in temperature differential, or 9 degrees Fahrenheit. Changes of more than 25 degrees Celsius, or 45 degrees Fahrenheit, were linked to a greater increase in heart attack rates compared to a smaller increase with temperature swings of 10 to 25 degrees Celsius, or 18–45 degrees Fahrenheit, according to the researchers.
The effect was more pronounced on days with a higher average temperature. In other words, a sudden temperature swing seemed to have a greater impact on warmer days, the researchers said. Based on their calculations, the researchers predicted there could be nearly twice as many heart attacks on a hot summer day with a temperature fluctuation of 35 to 40 degrees Celsius, or 63 to 72 degrees Fahrenheit, than on days with no fluctuation. “That is a striking increase,” Gurm said.
The researchers adjusted for precipitation totals, day of the week and seasonal trends to isolate the effects of daily temperature fluctuations from other potential environmental factors.
“Generally, we think of heart attack risk factors as those that apply to individual patients and we have, consequently, identified lifestyle changes or medications to modify them,” Gurm said. “Population-level risk factors need a similar approach. Temperature fluctuations are common and [often] predictable. More research is needed to better understand the underlying mechanisms for how temperature fluctuations increase the risk of heart attacks, which would allow us to perhaps devise a successful prevention approach.”