Houston, Texas, USA : Heart attacks happen more frequently in winter, a major Swedish study has confirmed. The research which was published today in JAMA Cardiology found the incidence of heart attacks in a sample of more than one-quarter of a million people increased with lower air temperature, lower atmospheric air pressure, higher wind velocity and shorter sunshine duration.
They saw the most pronounced association with air temperature. An increase in 7.4℃ was associated with a 2.8% reduction of heart attack risk.
The study involved more than 274,000 Swedes who had heart attacks between 1998 and 2013. Researchers looked up the weather on the day of each heart attack, to see if certain conditions appeared to make people more prone to heart problems.
Air temperature had the most profound effect on heart attack risk, with risk greater when the temperature dropped below 32 degrees F. But short days of sunshine, brisk winds and lower air pressure also were linked to increased risk.
Researchers found “an increase in heart attacks in low temperature, strong wind, low sunshine duration and low atmospheric pressure,” said senior author Dr. David Erlinge, head of cardiology at Lund University in Sweden.
The observed increase in heart attack risk could be due to weather’s effect on the circulatory system, Erlinge explained.
“We know that cold and wind cause the body to contract the blood vessels of the skin to preserve temperature and energy,” Erlinge said. “This causes the heart to pump against higher resistance, which increases the stress on the heart and may trigger a heart attack.”
Reduced physical activity, dietary changes and depression are other behavioral factors that could influence seasonal heart attack risk, the researchers added.
Folks also might be more prone to respiratory infections and flu during this type of weather, and those illnesses are known risk factors for heart attack. For example, it’s been shown that a respiratory infection can cause a six-fold increase in the risk of heart attack, the researchers noted.
If you’re concerned about your heart health, take the time to slip on a sweater or jacket during brisk days, or bundle up when the mercury takes a deep dive, Erlinge said.
“If you are at high risk, you may avoid going out in really cold, windy weather,” Erlinge added.
However, the news isn’t all worrisome.
The risk of heart attack decreased about 3 percent for every 45-degree Fahrenheit (F) increase in minimum air temperature, the study reports.
“It’s important to note the overall effect here is quite modest,” said Dr. Usman Baber, an assistant professor of cardiology at the Icahn School of Medicine at Mount Sinai in New York City.
However, the study can’t prove a cause-and-effect relationship, and Baber noted that many other factors may also be at play.
“I suspect the basis for this observed association is going to be more complex than that,” Baber said. “Physiology may play a role, but other factors like patient behavior that varies with weather might play a role.”
“When weather changes, people may behave differently,” Baber continued. “Maybe they are more stressed. Stress plays a major role in heart attack risk. Maybe people don’t take medications as frequently.”
Doctors have long acknowledged heart attacks are more likely to occur in cold weather. Every medical student over the past five decades has seen medical artist Frank H Netter’s classical illustration of a middle-aged man clutching his chest as he steps out of a warm building into a cold winter’s night.
Not all heart attacks are typical but in the mind of Netter and his medical advisers of the time, there is nothing more typical than that.
It is well documented that heart attack rates rise soon after a major natural disasters such as an earthquake, volcanic eruption or tsunami. These probably bring forward the timing a heart attack that was going to happen anyway as there are slightly fewer heart attacks a few weeks later.
But natural disasters are of course unpredictable, so we can’t prepare for them in the same way as some natural rhythms: night and day, summer or winter, wet or dry seasons. This is why research that confirms something we can plan for is a risk factor is important.
Predicting heart attacks
Reasons for why someone is prone to a heart attack are clear. These are obvious risk factors such as high blood pressure, abnormal cholesterol, smoking or diabetes as well as unseen underlying genetic and environmental factors. But the the reasons for the timing of heart attack are more difficult to understand.
Atherosclerosis, the underlying disease process leading to blockage of a coronary artery and heart attack, develops over many decades. There appears to be randomness to when thrombosis, the blood clot that forms in a vein or artery and causes the final and sudden event, occurs. It can occur during sleep, emotional stress and extreme physical activity – but more commonly, it occurs when not much is happening at all.
Then there are other people with advanced coronary artery disease who have never had a heart attack. If we knew more about the short-term triggers, we could help people with coronary disease avoid some of them. And if we knew some of the longer-term influences on rates, we could tailor scarce resources in the emergency and health systems to be ready for peak periods.
Why is winter riskier?
There is a clear association between cold and artery function (the vessels that deliver oxygenated blood from the heart to other parts of the body). This can be illustrated by a common physiology lab manoeuvre known as the cold pressor test. People are asked to put their forearm into iced water. Blood pressure rises immediately because arteries constrict, presumably to maintain core body temperature at normal levels.
Simple hydrodynamics tells us constriction is more profound and impacts more on the flow through a tube – in this case a coronary artery – at points of obstruction. In a few people with coronary disease the cold pressor test is enough to cause the artery to spasm and for flow to cease until the artery relaxes again.
But there are other factors that make heart attack more likely in winter than in summer. In many places, air pollution is more common, and evidence is accumulating that certain particles in the air are related to heart disease. Winter is also flu season, which makes people already at risk of heart disease more vulnerable.
And our life is very different in winter than in summer. Studies performed by myself and my colleague Dr. Gillian Deakin while she spent a year on a polar station in Antarctica demonstrated this. In winter it is always dark, and the weather prevents expeditioners doing much outside activity; they tend to put on weight and drink more alcohol.
Inevitably emotions are high when a disparate group is confined to a small area for a long time and away from their families and other everyday supports. Not surprisingly, their heart health was not the same as when they arrived. Blood pressure was higher and the metabolic pattern of their blood less healthy. This was remedied with a regular supervised exercise program.
In summer there was a general feeling of “joie de vivre” as expeditioners conducted most of their work activities for the year. These often involved long hikes, moving large items of equipment and other physically demanding tasks. More light and milder weather allowed more time for outside leisure activities too as they explored the extraordinary Antarctic landscape and fauna.
Their blood pressure and metabolic profile improved markedly. The same exercise program they had undertaken in winter did little to improve these further as they were already at peak or near peak fitness.
What about heat?
This is an extreme example of what happens to many of us in temperate climates across the seasons and most smaller studies have reported a similar pattern to Sweden. Sudden variations in temperature also seem to be associated with heart attacks.
In Sweden and Antarctica there are very cold winters and much warmer summers. What about in the tropics where extreme heat is a defining climatic feature. A study in Pakistan also found a winter peak in admissions to coronary care units in winter. However, there was another peak in mid-summer when temperatures were highest.
So, by all means keep warm and comfortable in winter but get out and do something too. Look after your risk factors and see your doctor regularly for a heart check.
Citation : David Erlinge, M.D., Ph.D., cardiology head, Lund University, Lund, Sweden; Usman Baber, M.D., assistant professor, cardiology, Icahn School of Medicine at Mount Sinai, New York City, JAMA Cardiology
A second study in Taiwan also found that when temperatures fall, heart attack risk may rise:
When temperatures fall, heart attack risk may rise
Colder weather may raise the risk for a heart attack, a preliminary study suggests.
Researchers in Taiwan found that heart attack rates fluctuated seasonally, with more occurring in winter than summer. When the temperature fell below 59 degrees Fahrenheit, heart attacks increased dramatically, the study authors said.
“When the temperature drops, people at high risk of a heart attack should be put on alert for symptoms such as chest pain and shortness of breath,” said study author and cardiologist Dr. Po-Jui Wu.
For the study, the researchers analyzed health records from more than 40,500 Taiwanese heart attack patients from 2008 to 2011.
That information was then stacked up against two other databases. One contained information about nearly 920,000 adults who had never had a heart attack, while a second tracked local weather patterns collected by the Taiwan Central Weather Bureau.
The researchers found that colder weather, changes in weather, and strong winds each were tied to increased heart attack risk the next day.
The study couldn’t prove a cause-and-effect relationship. However, the researchers advised taking public health measures to alert high-risk patients—perhaps via smartphone messaging—when problematic weather changes are coming.
“At-risk groups include people who had a previous heart attack, the elderly, or those with risk factors such as diabetes, high blood pressure, smoking, obesity, and sedentary lifestyles,” said Wu, of Kaohsiung Chang Gung Memorial Hospital in Kaohsiung City, Taiwan.
The findings were presented this week in Taiwan at a meeting of the Asian Pacific Society of Cardiology.
“Heart attacks can cause people to die suddenly, so it is essential to urgently seek medical assistance when symptoms occur,” Wu added in a news release from the European Society of Cardiology.