The Truth About Cats: They're Good for Us

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Cats: good for your health?
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THE GIST

- Cats have gotten a bad health rap, as new research suggests they may be beneficial to human health.

- Cats could even help to lower human risk of cancer.

- Cats may harbor T. gondii, but feline ownership does not predict risk of infection with this parasite.

News headlines over the past few years have linked cat ownership to everything from cancer to craziness, but new studies suggest that cats are actually beneficial to human health, and may even reduce our risk for cancer and other diseases.

Reports in this week's issue of Biology Letters, for example, counter the tabloid-suggested link between cats and human brain cancer.

Marion Vittecoq of the Tour du Valat research center and her colleagues conclude that cats should not be blamed for human cancer. In fact, studies show just the opposite.

Vittecoq told Discovery News that "according to our knowledge, studies that have focused on the link between cancer and cat ownership so far have found either no association at all or a reduced risk of cancer in cat owners."

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As an example, she and co-author Frédéric Thomas cite a National Institutes of Health Study by G.J. Tranah and colleagues. It found dog and cat owners have a reduced risk of non-Hodgkin's lymphoma. The longer the duration of pet ownership was, the less chance the individual would suffer from this type of cancer.

Why cats and dogs may benefit human health remains a mystery, but another study from earlier this month provides some intriguing clues. It found that infants having pets at home suffered from fewer respiratory tract illnesses.

"Our findings support the theory that during the first year of life, animal contacts are important, possibly leading to better resistance to infectious respiratory illnesses during childhood," wrote Eija Bergroth and colleagues in the paper, published in the journal Pediatrics.

Countless other studies demonstrate the mental health benefits of pet ownership, particularly for students, seniors and people with chronic illnesses. In such cases, pets can provide much needed comfort and companionship.

Cats have gotten a bad rap over the years, however, for a few different reasons. One is based on old ridiculous superstitions, such as how black cats are bad luck. The other, however, centers on a scientific debate concerning cancer and the protozoan parasite Toxoplasma gondii.

In earlier research, Vittecoq and Thomas determined that there is a positive correlation between this parasite and incidence of brain cancer. Cats can host this bug, and therein lies the "felines are bad for you" media frenzy over the past several months.

But the authors themselves indicate that cats have been mistakenly maligned, due to the other studies supporting the health benefits of cats, the fact that the connection between the parasite and cancer has still not been firmly established.

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Thomas explained that "humans usually get infected through the consumption of undercooked meat, especially sheep, containing asexual stages of T. gondii" or through contact with contaminated soil (which good hygiene remedies). Other studies show that ingestion of the bug in contaminated water, fruit, vegetables, and raw goat milk can lead to infection. The parasite is therefore somewhat similar to E. coli, in terms of transmission routes.

Victoria Benson of Oxford University's Cancer Epidemiology Unit, and her team also have a statement in the latest Biology Letters addressing this matter.

Benson and her team are conducting what's called the "Million Women Study," which investigates a tremendous amount of data concerning middle-aged women from the U.K. The scientists found zero association with incidence of brain cancer and women living with a cat.

"This, however, does not rule out the possibility that T. gondii infection from another source may be associated with brain cancer incidence," Benson and her team write.

If that other source, which may even be another parasite, is found, Thomas says it could "provide a means to reduce the risk of brain cancer, particularly in countries like France where the incidence of brain cancer and T. gondii are both high."