Will Global Warming Increase Heart Disease?

I was surprised to see this article in the International Herald Tribune suggest that global warming might cause increased incidence of cardiovascular death. In particular one statement struck me as being somewhat absurd.

On the sidelines of the European Society of Cardiology's annual meeting in Vienna this week, some experts said that the issue deserved more attention. It's well-known that people have more heart problems when it's hot.

During the European heat wave in 2003, there were an estimated 35,000 deaths above expected levels in the first two weeks of August. In France alone, nearly 15,000 extra people died when temperatures soared. Experts say that much of that was due to heart problems in the elderly worsened by the extreme heat.
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The hardening of the heart's arteries is like rust developing on a car. "Rust develops much more quickly at warm temperatures, and so does atherosclerosis," said Dr. Gordon Tomaselli, chief of cardiology at Johns Hopkins University and program chair at the American Heart Association.

In higher temperatures, we sweat to get rid of heat. During that process, blood is sent to the skin where temperatures are cooler, which opens up the blood vessels. In turn, the heart rate rises and blood pressure drops. That combination can be dangerous for older people and those with weakened cardiovascular systems.

That's interesting. It makes you wonder why all those old people move to Florida if increased heat is actually dangerous for older people. There are problems with this report, and while increased temperatures do cause some cardiovascular problems, they decrease others, and the picture is more complicated than this article would suggest.

First of all, let's address this suggestion that atherosclerosis develops more at warm temperatures. I'm sorry, but this is an absurd statement. First of all, your body thermoregulates, and shifts in external temperature do not cause oxidation in your blood vessels like heating metal. This is a terrible analogy.

Second, research into cardiovascular deaths and temperature shows a mixed bag of effects. In this study of hospitalizations for cardiovascular death in Denver, warmer temperatures correlated with increased MI admissions for those older than 65, but lower admissions for coronary atherosclerosis (contrary to the rust analogy), and pulmonary heart disease. Small increases in relative risk of congestive heart failure admissions and acute MI occurred.

One also has to remember that it isn't necessarily temperature itself causing these admissions, on warmer days people are more active, outside more, and increase their exposure to environmental pollutants, known to increase heart attack risk which are elevated on warm days as well. And as Jonah has recently pointed out, cold weather kills too, especially when areas that are used to mild weather experience cold weather. I can find no published research that suggests in warmer climates there is increased atherosclerosis. If anything, as cold weather tends to make people more sedentary, fat and lazy, evaluations of causes of death in different countries would suggest warmer countries experience less ischemic heart disease, when statistics are age-adjusted. Further, studies in countries like Finland show cold is associated with more cardiovascular mortality, and while heat causes excess deaths as well, it's probably on the order of 10x less. The data across multiple studies suggest the lowest mortality occurs around a temperature of 15 degrees celsius (about 60 degrees farenheit). It also matters what country you are in. A hot day in New Delhi, for instance, is far more deadly than a hot day in London, again showing the importance of air quality, technology, climate control etc., on mortality.

So, will warmer temperatures result in a net increase in cardiovascular deaths? Well, maybe, but mainly through the secondary consequence of increased air pollution that worsens air quality on hot days. The good news is that even in the context of global warming these consequences can be addressed through better technology. The introduction of the catalytic converter is one of the great successes in environmental regulation, greatly improving air quality within a decade in the US. Further emphasis on reducing emissions, especially particulate emissions, and CO, and NO2 from vehicular emissions (since they occur at street level they increase risk more than say, a coal-fired plant out in the country side). Overall the relative increases in risk of cardiovascular events from heat are small, and can be avoided by at-risk individuals by staying indoors when the air-quality is poor, and limiting exertion in warm weather. Far greater improvements in mortality from heat-excess could be achieved in the third world by emphasis on cleaner burning engines, use of catalytic converters, and decreasing ambient air pollution.