Science has transformed our society and culture. One of the remarkable aspects of science is the effect over years: as more is discovered, so our pool of knowledge gets bigger and bigger. In theory, at least, this should lead to the human race gradually becoming more informed, and closer to the "real" truth of the world around us.
I've recently come across a new scientific paper which investigated the reputed benefits of dog ownership to human health by gathering and analysing the combined research of the past seventy years. This has significantly added to our understanding on the benefits brought to us by pets.
For a long time, there have been hints that dog ownership may be associated with decreased cardiovascular risk, but up until now, the research has sometimes seemed ambivalent. A series of studies suggested associations of dog ownership with lower blood pressure levels, improved lipid profile, and diminished sympathetic responses to stress. These results were enough to persuade the American Heart Association to issue a statement in 2013 which concluded that "dog ownership is probably associated with decreased cardiovascular risk'. But other studies were less certain, claiming that the overall impact of living with a dog was neutral.
The paper that I read recently was a systematic review and meta-analysis, titled "Dog Ownership and Survival". This has added definite evidence to the debate, by reviewing a very high number of studies, published between 1950 and 2019.
The background to this is that animal companionship, in particular dog ownership, has become increasingly common. It's estimated that two thirds of Irish homes own a dog. The recognised health benefits of dog ownership include reduced risk of asthma and allergic rhinitis in children exposed to pets in their early years, improvement in well-being and alleviation of social isolation in elderly individuals, and increased physical activity in people of all ages. I've always said that doctors should write prescriptions for pet ownership for some people.
Despite these benefits, the definite evidence for an impact of dog ownership on actual mortality has been frustratingly conflicting. There has been a lack of randomised clinical trials evaluating the impact of dog ownership on cardiovascular disease prevention: this is the gold standard for evidence. It's like doing an experiment: give half of the people dogs, and watch what happens.
One trial of this type was done recently: an interventional study of nearly fifty people with high blood pressure involved choosing a random selection of them to acquire a pet. This showed that pet owning was linked to lower blood pressure when faced with mental stress six months later. In addition, among dog owners, the act of petting a dog has been specifically been shown to lower blood pressure levels when compared with other activities.
Other interventional studies have been more difficult to do, especially when looking at overall mortality. That is why the authors of this recent paper decided to tale a different research approach: an evaluation of as much observational data as they could find.
They carried out a detailed long term analysis of all past studies that have looked at the association of dog ownership with cardiovascular mortality. They started out with over a thousand research papers over seventy years, but narrowed these down to just ten that were specific enough, and high enough quality, to be included: these studies included data from nearly four million people, making the results very significant.
The researchers compared the number of deaths in dog owners (so-called "exposed group") to the number of deaths in individuals who do not own dogs ("control group"). The results are remarkable: dog ownership conferred a 65% risk reduction for mortality following myocardial infarction, as well as a 31% risk reduction on cardiovascular mortality overall.
This is enough evidence to strongly support dog ownership as a way of helping people to be healthier and live longer.
Why is dog owning so positive in these ways? The simplest answer is to suggest that the physical activity of dog walking brings benefits. It is true that dog owners walk significantly more than non-owners, and are more likely to achieve recommended level of physical activity .
My own sense is that the benefits come from far more than just physical exercise: owning a dog changes your life in a wide range of positive ways, from making you more social (everyone who has a dog knows that you're far more likely to stop to talk to other dog owners when on walks), to making your home more cosy (there is a huge difference between coming home to a cold empty house, or being greeted by a friendly, enthusiastic dog). There's the positive psychological impact of a dog forcing you to look outwards rather than inwards. I could write an entire column about the many ways that a dog makes you feel better.
So it isn't all about heart disease. But given that this is such a common cause of mortality in our culture, the positive effect of dogs on survival is a message well worth spreading. Tell all your friends!