The benefits of heart disease

Via Jerry Coyne: a delightful paper arguing that depression is an evolutionary adaptation. I was so enamored of the argument that I applied it to another medicalised and unfairly demonised condition: heart disease.

Heart disease seems to pose an evolutionary paradox. Research in the US and other Western countries estimates that between 30 to 50 percent of people will die of cardiovascular disease at some time in their lives. But the heart plays crucial roles in promoting survival and reproduction, so the pressures of evolution should have left our hearts resistant to such high rates of malfunction. Cardiovascular disorders should generally be rare — why isn’t heart disease?

Perhaps heart disease should not be thought of as a disorder at all. In an article recently published, we argue that heart disease is in fact an adaptation, a state of health which brings real costs, but also brings real benefits.

One reason to suspect that heart disease is an adaptation, not a malfunction, comes from research into lipids. “Hundreds of publications on research with pigs as human models have reported scientific information on cardiovascular physiology, obesity, stress,…diabetes, drug metabolism,… as well as many aspects of nutrition. Dental characteristics,…cardiovascular anatomy and physiology, and digestive anatomy and physiology of the pig and human are similar, as well as lipoprotein and cholesterol metabolism.” Even though pigs are ungulates occupying a very different ecological niche to early humans, this similarity of function suggests that lipid metabolism is so important that natural selection has preserved it. The ability to “turn on” heart disease would seem to be important, then, not an accident.

This is not to say that heart disease is not a problem. People with heart disease often have trouble performing everyday activities, they can have long periods of being unable to work, they tend to withdraw from many social activities, they are lethargic, and they often lose the ability to take pleasure from such activities such as exercise and sex. Some can plunge into severe, lengthy, and even life-threatening bouts of heart failure.

So what could be so useful about heart disease? People with heart disease often reduce their level of physical activity. As they reduce their exercise level, less demand is made of the heart. Thus heart disease often results in people placing less stress on their heart, thus reducing their risk of heart disease. This may explain why heart disease is so evolutionarily important.

But is there any evidence that heart disease is useful in preventing heart attacks? For one thing, if physical inactivity were harmful, as most clinicians and researchers assume, then bouts of heart disease should be faster to resolve when people are given interventions that encourage physical activity. However, the opposite appears to be true. Several studies have found that physical activity increases the risk of acute heart attacks, and they suggest that this is because increased cardiovascular demand can create acute lack of oxygen to heart tissue.

There is another suggestive line of evidence. Various studies can be misinterpreted to find that people with heart disease, being more prone to obesity, are better at floating. Yet drowning would seem to have been precisely the kind of problem important enough to drive the evolution of such a costly process. Consider a woman who discovers herself in the middle of the Pacific Ocean. Is the woman’s best strategy to ignore her situation, or to try to swim to Easter Island, or to simply give up and sink? In vivo experiments indicate that floating people are more likely to survive long enough to be rescued.

Heart disease is nature’s way of telling you to reduce the load on your heart. Therapies should try to encourage physical inactivity and atherogenesis rather than try to stop it. It is also essential, in instances where there is resistance to a sedentary lifestyle and high-fat diet, that the therapist try to identify and dismantle those barriers.

When one considers all the evidence, heart disease seems less like a disorder where the heart is malfunctioning. Instead, heart disease seems more like the vertebrate eye—an intricate, highly organized piece of machinery that performs a specific function.

Perhaps heart disease should not be thought of as a disorder at all. In an article recently published, we argue that heart disease is in fact an adaptation, a state of health which brings real costs, but also brings real benefits.
One reason to suspect that heart disease is an adaptation, not a malfunction, comes from research into lipids. Hundreds of publications on research with pigs as human models have reported scientific information on cardiovascular physiology, obesity, stress, dermatology, teratology, toxicology, immunology, behavior, hemodynamics, renal physiology, experimental surgery, gastroenteritis, diabetes, drug metabolism, and perinatology as well as many aspects of nutrition. Dental characteristics, renal morphology and physiology, eye structure and visual acuity, skin morphology and physiology, cardiovascular anatomy and physiology, and digestive anatomy and physiology of the pig and human are similar, as well as lipoprotein and cholesterol metabolism. Even though pigs are ruminants occupying a very different ecological niche to early humans, this similarity of function suggests that lipid metabolism is so important that natural selection has preserved it. The ability to “turn on” heart disease would seem to be important, then, not an accident.
This is not to say that heart disease is not a problem. People with heart disease often have trouble performing everyday activities, they can have long periods of being unable to work, they tend to withdraw from many social activities, they are lethargic, and they often lose the ability to take pleasure from such activities such as exercise and sex. Some can plunge into severe, lengthy, and even life-threatening bouts of heart disease.
So what could be so useful about heart disease? People with heart disease often reduce their level of physical activity. As they reduce their exercise level, less demand is made of the heart. Thus heart disease often results in people placing less stress on their heart, thus reducing their risk of acute heart attacks. This may explain why heart disease is so evolutionarily important.
But is there any evidence that heart disease is useful in preventing heart attacks? For one thing, if physical inactivity were harmful, as most clinicians and researchers assume, then bouts of heart disease should be faster to resolve when people are given interventions that encourage physical activity. However, the opposite appears to be true. Several studies have found that physical activity increases the risk of acute heart attacks, and they suggest that this is because increased cardiovascular demand can create acute lack of oxygen to heart tissue.
There is another suggestive line of evidence. Various studies can be misrepresented to find that people with heart disease, being more prone to obesity, are better at floating. Yet drowning would seem to have been precisely the kind of problem important enough to drive the evolution of such a costly process. Consider a woman who discovers herself in the middle of the Pacific Ocean. Is the woman’s best strategy to ignore her situation, or to try to swim to Easter Island, or to simply give up and sink? In vivo experiments indicate that floating people are more likely to survive long enough to be rescued.
Heart disease is nature’s way of telling you that you’ve got clogged arteries. Therapies should try to encourage physical inactivity and atherogenesis rather than try to stop it. It is also essential, in instances where there is resistance to inactivity and high-fat diet, that the therapist try to identify and dismantle those barriers.
When one considers all the evidence, heart disease seems less like a disorder where the heart is malfunctioning. Instead, heart disease seems more like the vertebrate eye—an intricate, highly organized piece of machinery that performs a specific function.

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