Heart-Stopping Stupidity: Climate Change Isn't Increasing Heart Attacks

“Rise in heart disease may be explained by extreme weather conditions,” ABC News reported last week. Reasonable measures like avoiding cigarettes and eating well help prevent heart disease, the news outlet acknowledged, but “doctors agree that protecting yourself from the impacts of climate change is essential to your heart health.”

ACSH is a family-friendly organization, so I'll put this as gently as possible. ABC news is shoveling an eight-letter word that works well as garden fertilizer. There is no reason to believe that climate change is seriously jeopardizing our heart health.

Here's the first major problem, from the ABC story itself:

It's not clear exactly why temperature shifts are correlated with higher rates of heart attacks. Experts believe that temperature shifts affect the body's ability to regulate normal body temperatures in response to the extreme temperatures.

This may be my ignorance speaking, but why are researchers and journalists presenting this association to the public before they know it's meaningful? If they don't know how temperature shifts impact heart attack rates, they don't know if the correlation is concerning. Is there data showing that “extreme” temperatures are hindering our ability to regulate body temperature? Let's see it. Until we do, there's several reasons to be skeptical of this correlation.

We're good at preventing heart disease

First and most importantly, heart-disease mortality rates have been declining in the developed world for decades. According to a 2017 study,

Since 1978, a sharp decline in mortality rates from CHD and stroke has become unmistakable throughout the industrialized world, with age-adjusted mortality rates having declined to about one-third of their 1960s baseline by 2000.

That trend has continued in recent years. Breaking out some of the results illustrates just how significant the decline has been:

• Adjusted by age, annual heart disease mortality per 100,000 fell by 56 percent from 307.4 in 1950 to 134.6 in 1996.

• Age-adjusted annual stroke rates per 100,000 fell by 70 percent during this same period, declining from 88.8 to 26.5.4

• Annual age-adjusted cardiovascular mortality rates continued to decline, falling 22 percent from 376 to 274 per 100,000 from 1990 to 2013.

• Similar declines have been observed in nearly all regions of the world, especially in high-income North America, Western Europe, Japan, Australia, and New Zealand.

The authors went on to conclude:

In most of these countries, the declines in CVD mortality rates have been phenomenal - more than 70% decline in men and women in the Netherlands; and over 60% decline in the United Kingdom and Ireland - from 1980 through 2009.

Someone could object that we've just gotten better at treating heart attacks over the years, which has cut mortality rates dramatically; climate change could still be contributing to a rise in heart attacks. While plausible, improved treatment isn't the whole story. Countries that have reduced heart-disease mortality have also seen dramatic declines in smoking, improvements in hypertension treatment and control, and widespread use of cholesterol-lowering drugs.

The fact of the matter is this: the impact of heart disease, though still significant, has declined as the global average temperature has trended upward. The same boring risk factors still drive your heart-disease risk; control those variables and your risk plummets. We know this, in part, because the decline in heart disease mortality has decelerated recently while the "Prevalence of obesity, metabolic syndrome, and type 2 diabetes have increased during the past 20 years," the authors of the 2017 paper added. 

It's all heart disease to me

Even researchers who promote the climate-heart attack hypothesis have come close to accepting this important conclusion. The authors of an October 2020 article in Nature Reviews Cardiology argued that temperature increases between 2001 and 2014 had “significant effects” on myocardial infarction risk, but they also acknowledged that

The increased risk was attributable to the greater vulnerability to cardiovascular disease of individuals with type 2 diabetes mellitus or hypertension.

This is a crucial qualifier because news reports often overlook these risk factors, or confuse heart disease with unrelated conditions. The ABC story began with an anecdote about a physician watching a "healthy athlete die of heat stroke." As Medscape notes,

When heat gain overwhelms the body's mechanisms of heat loss, the body temperature rises, potentially leading to heat stroke. Excessive heat denatures proteins, destabilizes phospholipids and lipoproteins, and liquefies membrane lipids, leading to cardiovascular collapse, multiorgan failure, and, ultimately, death.

The imbalance between heat loss and gain is driven primarily by physical exertion; a related outcome called classic nonexertional heat stroke (NEHS) "more commonly affects sedentary elderly individuals, persons who are chronically ill, and very young persons," Medscape adds. But I hasten to repeat that neither of these is heart disease.

We manage heat waves well, too

Looking at the actual numbers in their proper context confirms that neither heat stroke nor heart disease is killing people en masse during heat waves. The EPA estimates that excessive heat has caused or contributed to approximately 11,000 deaths since 1979. Since 1999, the agency reports, "the interaction of heat and cardiovascular disease caused about one-fourth of the heat-related deaths recorded in the 'underlying and contributing causes' analysis ...'" [1]

Crucially, many such deaths have been prevented because past heat waves have incentivized investment in infrastructure that mitigates the danger linked to sweltering summer days. [2] Multiple studies have shown that heat-related deaths tend to decline after large temperature spikes. Parenthetically, cold kills far more people worldwide than extreme heat.

When we compare the relatively small estimates of heat-related death to the annual figures for heart-disease mortality, the picture becomes clear very quickly. Coronary heart disease killed almost 400,000 people in 2020 alone. The contribution of climate change to heart attacks is a (very manageable) drop in the bucket against this backdrop.

Exaggeration has consequences

Activist groups regularly complain about “climate change denial.” But it's not really difficult to see why this skepticism persists: if you inflate the danger people face, you abuse their trust; eventually, they tune you out. Think about that observation in the present context. At the same time that deaths due to heart disease and natural disasters are declining, some scientists and journalists are blaming heart attacks on global warming.

This is the sort of fear-mongering and speculation we've come to expect from fringe environmental groups and kooky politicians; it serves no purpose except to make science communication more difficult. University of Oxford environmental scientist Dr. Hannah Ritchie has issued the very same warning about climate doom and gloom. Let's give her the last word:

… [D]oomsday scenarios play into the hands of climate skeptics. When the world doesn’t end in 10 years, the whole field of climate science takes a hit. People assume this message came from scientists—which it didn’t—and their reputation becomes tarnished. The public loses trust in them.

[1] According to the EPA, the relevant data only became available in 1999.

[2] These adaptations include air conditioning, improved medical care, early-warning systems, and public cooling centers.