by Nigel Barber Ph.D.: Dogs improve health behavior more than they change health directly…
It was startling to read recent exaggerated claims that owning a dog could increase life expectancy by about 10 times as much as being married. The findings provide a cautionary tale in how scientific results are interpreted.
The News May Be Too Good
The results of a recent study published by the Mayo Clinic suggest that some people live much longer if they are dog owners. The study populations were Swedish heart attack and stroke patients.
This means that the findings tell us little, or nothing, about the general population. It is a truism of statistical inference that the results for a specific population cannot be extended to different populations.
Even so, the numbers are startling. The study reports that heart attack and stroke patients live more than 20 percent longer if they are dog owners compared to non-dog owners.
To put this in context, we are dealing with a boost to health that is an order of magnitude greater than the lifelong benefit of being married.
As such, it seems too good to be true. While the study seems to have been rigorously conducted, it is possible that something went wrong.
Once again, basic statistical inference could be in play. One anomaly of the study was extremely low dog ownership rates of study participants. At less than 5 percent, the dog ownership rates were strikingly low in a country (Sweden) where 24 percent of the population owns dogs according to recent surveys.
The criteria of dog ownership may have been too restrictive, introducing a distortion in the study if the population of dog ownership among heart and stroke patients was under-represented and non-representative.
Whatever about this clinical population, there are good reasons for believing that dog ownership can confer health benefits.
The Nitty Gritty of How Dogs Affect Health
Owning any pet may well confer psychological benefits and improve somatic health. Yet, the focus on dogs is not difficult to explain.
To begin with, dogs are mostly very generous with their affection. They provide positive interactions that are reliable and have little to do with how the owner feels, or acts. Unconditional affection is the gold standard by which intimate emotional relations among people are judged.
Such relationships protect us against loneliness and depression so that dog ownership can produce beneficial psychological outcomes.
Another key reason that dog ownership contributes to health is that it makes people more physically active. This helps explain why health researchers have zeroed in on canine companions rather than other common pets, such as cats.
Most cats do not need to be walked and most also show limited affection. The affection expressed by cats is also less predictable, evidently depending upon how the individual animal feels at a specific time. These factors may be why cat ownership attracts less attention from health researchers.
What of the evidence for health effects from dogs?
Health Effects in a Random Sample of Czechs
Given that dog owners walk more and spend more time outdoors in pleasant natural scenery, one might expect them to have better cardiovascular health. That is indeed the case.
That conclusion is widely known and was confirmed in a high-quality study conducted in the city of Brno in the Czech Republic (Czechland).
This study improved over others by randomly selecting subjects and conducting lab measurements related to cardiovascular health. Using this superior methodology, researchers found substantial health advantages among dog owners.
Yet, the benefits of dog ownership on health disappeared when controlling for age, activity level, and socioeconomic status of the participants.
Reading between the lines, it appears that much of the health advantages of dog ownership overlap with the benefits of exercise in improving cardiovascular health. Owning a dog motivates owners to get more exercise so that they can expect to be healthier.
While owning a dog generally contributes to health, it can also have downsides.
How Dog Ownership Can Undermine Health
Dog ownership can be a source of health problems. To begin with, older people are more vulnerable to tripping and falling particularly when walking an enthusiastic large canine. Dogs have short lives compared with people so that their loss is a cause of recurrent bereavement that can trigger depression in vulnerable individuals.
Domestic dogs suffer a great many illnesses that are almost as expensive to treat as human health problems. Even when healthy, a dog is a drain on finances that may be a significant burden for low-income households. Financial strain is a major source of stress in people’s lives and can undermine health.
The responsibility of caring for a pet can be socially isolating if owners feel obliged to stay at home to care for their animals. Social isolation is also a threat to health.
Despite such problems, the recent findings suggest that dog ownership can boost health substantially. This benefit probably reflects higher levels of physical activity.