In the mid-1980s doctors noticed that many patients recovering from heart attacks had a particular type of arrhythmia. What's more these arrhythmias were asymptomatic, meaning the patients had no idea they had it. Doctors suspected that these arrhythmias were responsible for
causing subsequent heart attacks, but they had no evidence. So in 1986 clinical researchers recruited hundreds of patients into the Cardiac Arrhythmia Suppression Trial (CAST). They hypothesized that a new class of drugs
would suppress these arrhythmias, reduce the likelihood of subsequent heart attacks, and save lives.
Six years later the data were all in and showed conclusively that arrhythmia drugs effectively suppressed asymptomatic arrhythmias (w00t!). Unfortunately, that was only the first part of the hypothesis. The drugs actually tripled the risk of dying from another heart attack. (Doh!)
So the hypothesis didn't pan out, but that's what makes it science. Another group of researchers looked deeper into the data, and found some interesting things. They calculated that if you've had a heart attack, your chance of dying within a year is about 5%. Unless you have a dog, then your likelihood of dying drops by a factor of 5, down to 1%. Dogs help people survive heart attacks. Unfortunately for cat fanciers, the feline data was less conclusive. Similarly, an Australian survey study of 1000 Australians showed that owners of dogs (and cats this time too), made fewer visits to doctors offices, were less likely to be on heart medication and had fewer sleep difficulties. However, kangaroo ownership didn't help at all.
In addition, the CAST data showed that having good social support also increased survival, as did low levels of anxiety. So dogs, social support, and low anxiety help prevent death from heart attacks. These all sound like a diverse set of causes, but is there possibly a common thread between them? For the answer we look to the parenting practices of rats. (But I mean obviously the answer is yes, otherwise why would I pose the question?)
You may recall from my last article that rat mothers lick their babies (some more than others), and that this releases the neurotransmitter/hormone oxytocin in the babies (Educational Sidenote: whether it's considered a neurotransmitter or a hormone just depends on if it's found in the brain/nervous system or in the rest of the body. Oxytocin is found in both places). Rats who get licked a lot as kids grow up to be less anxious and less stressed.
Oxytocin works similarly in humans, and while it may be particularly necessary in childhood, even during adulthood it is important. Oxytocin is released by physical touch (hugs, kisses, handshakes, massages, breast-feeding ... that sort of thing), and possibly even through social interaction. One study showed that girls release oxytocin when talking to their mother. Importantly, oxytocin reduces stress and the levels of stress hormones, and has many other positive effects.
So how does this relate to having a dog? A group of Japanese researchers wanted to know just that, so they examined changes in oxytocin levels when people played with their dogs. The study found that when dog owners had a strong relationship with their dog, playing with their dog increased oxytocin. Another study from South Africa showed that petting a dog, even a strange dog, not only increased oxytocin, but dopamine and endorphins as well*.
Looking again at the heart attack survival data, we start to see a connection between the factors influencing survival: dog ownership, social support and low anxiety/stress. Playing with dogs and interacting with people both release oxytocin, which reduces anxiety and stress. And it doesn't just stop there. Physiologically, oxytocin can lower blood pressure and heart rate. In rats oxytocin has also been shown to improve the healing of heart tissue after a heart attack.
Some of these effects are caused by oxytocin acting as a hormone directly on the heart. But many of the effects, like reductions in stress and anxiety, are caused by oxytocin acting as a neurotransmitter in the brain. Either way, oxytocin is good for you. It reduces anxiety, and the stress response. Given that chronic stress is one of the biggest causes of poor health, it's clear how beneficial oxytocin can be.
Humans are social animals. So I guess it's not that surprising that having support from other humans, and other animals, has positive health benefits. Hopefully you also take away from this article the fact that there is not always a clear divide between physical health and mental health.
So if you have heart attack, reach for your poodle. Well, reach for the phone first (or your LifeAlert), then maybe reach for the Aspirin, then reach for the poodle.
*Correction (5/14/12): This post originally included a reference to serotonin that was not corroborated by primary literature, and has been removed.
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