Unfriendly cat nips related to depression in owners, study finds

Research and common sense say that pets are good for your health. However, a recent study shows that, unfortunately, this may not always be the case.

Researchers at the University of Michigan and Virginia Tech have found a peculiar correlation between cat bites and depression. Of patients that sought medical attention for cat bites, 41.3 percent were also diagnosed with depression and, to add to the mystery, 85.5 percent of those who had both a cat bite and depression were women.

The study, led by David Hanauer, an associate professor at the University of Michigan Medical School, and published in PLoS One, combed through the electronic health records of the University of Michigan Health System. By looking at 1.3 million patients over a period of 10 years, the researchers were able to analyze correlations between animal bites, depression, gender and age. They also looked at the living situation of patients, recorded as living alone or with other people, to develop a rough estimate of social isolation.

The strongest correlation was between cat bites and depression for women. Of the women who saw a doctor for a cat bite, 47.0 percent were diagnosed with depression at some point in their lifetimes. For men who went to the doctor for a cat bite, the percentage that were diagnosed with depression was only 24.2.

This gender difference was also seen with dog bites. However, the gap was significantly smaller. A woman who presented with a dog bite had 35.8 percent of being diagnosed with depression; a man had 21.1 percent chance.

The research team did not aim to explain the reasons for the relationship between cat bites and depression with their study but they did offer possible explanations.

Cats and other animals are known to respond to changes in their owners’ mental states or responsiveness. It is further known that people who suffer from depression often make less eye contact than those who do not. Because cats can detect and react to human gaze and eye focus, it seems plausible that cats are more likely to bite owners who are already depressed.

However, the causation between cat bites and depression, if there is one, may go in the opposite direction. The researchers refer to a common parasite, Toxoplasma gondii, that is carried by cats. T. gondii can infect humans and produce long-term neurological effects that can cause schizophrenia, obsessive compulsive disorder and personality changes. This parasite has been linked in various studies to depression and depression-like symptoms. Such relation, despite the lack of definitive evidence, suggests that the cat bites may play a role in causing the depression.

Regarding the higher correlation for women, the researchers discuss the well-demonstrated fact that women are more likely to own and care for cats than men are. Women are also more likely to be diagnosed with depression. However, neither of these facts alone explains the numbers in the study. The different personality types associated with “cat people” and “dog people” may be relevant since women are more likely to be “cat people” than “dog people.” “Cat people” tend to have higher level of neuroticism, a trait that has been strongly associated with depression. The particular relationship between neuroticism and depression is unknown, however, and no one has conclusively demonstrated that neuroticism increases the vulnerability or risk for depression.

Pets themselves may, on some occasions, increase the risk of depression. The media has a tendency to report on the many studies that show the therapeutic and mental health-beneficial effects of owning pets. These benefits, which include lowered blood pressure and social support, are well-documented. However, the researchers of this study note that there has been research to the contrary. One study, for example, concluded that among people living alone, cat ownership had no effect on overall loneliness. Another found that, among those with low levels of social support, people who were more attached to their pets had more depression than people who were less attached. Many other studies have been inconclusive on the benefits or drawbacks of having pets, so the relation between cat bites and depression may not be as unbelievable as it first appears.

Depression in whole is a serious public health issue, affecting an estimated 18 percent of U.S. patients. Due to the results of their study, the researchers suggest adding cat bites to the list of warning signs that should prompt a screening for depression. Depression screening is not universal because the disease is often difficult to detect. Many doctors rely on symptoms such as irritableness and hostility, withdrawal from activities, suicidal thoughts and nonspecific somatic pains as cues that the individual may be depressed.

Despite the uncertainty surrounding these results, the researchers say that the correlation between cat bites and depression is strong enough to warrant the incorporation of cat bite data into scientific discussions of depression and to warrant further investigation.