- At age 71, one in every seven Americans shows symptoms of age-related dementia or Alzheimer's disease.
- Long-term dog ownership seems to be associated with fewer age-related declines in cognitive ability.
- One factor may be the effect of the "love hormone" oxytocin on brain function.
Some new data suggests that long-term ownership of a dog may help to offset the kinds of cognitive declines that we see in age-related dementia and Alzheimer's disease.
Given the fact that our population is living longer, coping with the reduced mental abilities of older individuals is becoming a larger problem. A recent study suggests that in the U.S., one in seven people, aged 71, is suffering from dementia or Alzheimer's disease. That number increases over time and by age 90 nearly one in three people may be affected. These dementias are characterized by a group of progressive, incurable neurological syndromes associated with irreversible memory loss and diminished cognitive abilities.
Dementia Is Not Inevitable
Research suggests that approximately one-third of dementia cases are associated with causes that can be controlled or modified, including physical inactivity, social isolation, cardiovascular disease, depression and chronic stress. Therefore, to try to reduce the effects of dementia, medical and psychological researchers are studying lifestyle habits that may decrease the likelihood or severity of such conditions. The surprise is that this is where dog ownership comes into play.
Interaction with a pet dog in the household is an important aspect of an older person's lifestyle that could influence their cognitive health. Living with a pet has been shown to have beneficial effects on many aspects of our physical and psychological welfare. Dog ownership is associated with better cardiovascular health, decreased loneliness and lowered likelihood of depression. It is well-established that a pet dog provides emotional support which in turn buffers an individual against the effects of stress. Jennifer Applebaum of the Department of Sociology and Criminology & Law at the University of Florida in Gainesville headed a team of researchers who wondered about whether the positive effects of dog ownership could help offset some of the cognitive declines observed in older individuals.
Tracking Age-Related Cognitive Decline
To study this question the team of researchers gathered data from the University of Michigan's Health and Retirement Study. This is a large ongoing, and continually evolving, data-gathering enterprise which draws upon a nationally representative and diverse group of U.S. adults aged 50 years and older. It is designed to investigate the health, social, and economic implications of aging in the American population. Every two years the survey collects a wide range of data including the medical health, cognitive ability, family status, employment and other factors from the approximately 20,000 individuals enrolled in the study. The scientists try to monitor these people from the age of 50 until the end of their lives, with follow-up measurements on a biennial basis.
To look at the effect of dog ownership on cognitive ability in seniors, a subset of 1,369 people were measured over a six year time span. This involved repeated measurements every other year from 2010 to 2016. The core of this current study is that at each of the four measurement sessions, participants were given four cognitive tests.
There were two numerical tests. The first involved simply counting backwards from a given number, while the second involved subtracting seven from a number and then continuing to subtract from the result until time ran out. The number correct served as the score.
The other two cognitive tests involved verbal memory. The first tested short-term memory where the individuals were asked to listen to a list of words and then repeat back as many as they remembered. The second verbal test was a delayed memory task, where, following the short-term memory test, they were given five minutes of other activities and then had to once again recall the lists that they had heard earlier. Remember, these individuals are being tested every two years, so that if there is any decline in their cognitive ability over the six year span of the tests, it should be visible.
A Long-Term Process
According to the reasoning of the research team, simply having a dog in the room, or petting one before a test should not provide any noticeable cognitive benefit. These scientists hypothesized that it was not a short-term interaction with a dog that makes a difference, but rather the cumulative effect of day-to-day interactions with a familiar pet dog over a sustained period of time which ultimately matters and provides the cognitive benefits. Therefore they divided the data into several analysis groups. Specifically they categorized data from individuals who were 65 years or older, versus those less than 65 years. The second categorization divided the group into people who had owned a dog continuously for five or more years, those who had owned a dog for less than five years, and non-dog owners.
During the first stage of data processing it became quite clear that when the investigators looked at a composite score of the four cognitive tests, there were no effects of pet ownership for individuals aged less than 65 years of age. When they looked at the group who was 65 years or older, however, they found that those who had owned dogs continuously for more than five years had a higher composite cognitive score for each measurement point across the six year test interval, as compared to those people who did not own pets or had owned a pet for less than five years.
The researchers went on to break down the scores further, and found a bit of a surprise. There was very little difference for the numerical tests based upon either age or pet ownership. Instead they found that most of the benefits of dog ownership for their older long-term pet owners came from the marked superiority of the 65 and older long-term pet owners on the verbal memory tests.
A Love Link?
The reason for this benefit from dog ownership is not clear; however the researchers speculate that one factor might have to do with the effect of oxytocin on brain function. Oxytocin is a hormone that is often called a "love hormone", or a "feel-good" hormone, that is released in people when a person has pleasant social interactions, including those interactions that humans may have with their dog. Some recent studies have suggested that oxytocin not only has the emotional effects associated with human/canine bonding, but it also affects social cognition and memory encoding in humans at the neurological level. The extra doses of oxytocin, over a prolonged period of pet ownership might be what's providing the cognitive benefits to seniors.
For whatever reason, based on their data these investigators conclude that "these findings provide early evidence to suggest that long-term pet ownership could be protective against cognitive disparities."
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