STRESS
July 24, 2010

Can Stress Do a Body Good?

Mice "stressed" by living in stimulating environments fought cancer better, suggesting a little stress may be good for you.

Contrary to intuition and to popular belief, a bit of stress may actually be good for the body. A team of researchers exposed the mice to a little stress – just a little – and then looked at how well their bodies fought off cancer.

The researchers found some significant changes in the bodies of the enriched mice. They weighed 6% less than control mice and had higher levels of stress hormone. They also had lower levels of leptin, a hormone that is involved in hunger but has also been shown to be involved in cancers, including melanoma.

Matthew J. During and his team placed one group of mice in an “enriched environment,” which was essentially community living for mice. These environments were more spacious than their normal cages, and there were plenty of toys and other mice to play (or fight) with. A second group of mice stayed in the old-fashioned, non-stimulating lab cages. All mice were injected with melanoma, which is a highly malignant form of skin cancer, and did not receive any form of cancer treatment.

After three weeks, tumors in the mice living in the stimulating, enriched environment shrank by 43%, and after six weeks they were 77% smaller than mice living in regular cages. In 17% of the enriched environment group, the tumors were completely gone.

How can this be? The researchers found some significant changes in the bodies of the enriched mice. They weighed 6% less than control mice and had higher levels of stress hormone. They also had lower levels of leptin, a hormone that is involved in hunger but has also been shown to be involved in cancers, including melanoma. The researchers outline the entire pathway, and showed that it is likely mediated by a brain chemical called brain-derived neurotrophic factor, or BDNF. Mice who were injected with colon cancer cells instead of melanoma showed similar improvements in cancer-fighting abilities.

If you were wondering whether the mice in the enriched environments were simply more active than control mice, and it was this that led to the better cancer outcome, the researchers thought of this, too. In a follow-up experiment, they gave mice in regular, non-enriched, housing exercise wheels to use as much as they wanted. These mice exercised quite a bit, and after the experiment was over, they weighed less and had more muscle than control mice. But they had lower stress hormone levels and their leptin levels were no different from controls. This finding suggests that the effects of the enriched environments did indeed stem from the extra stress and from changes in the leptin pathway.

What exactly it is about the enriched environments that led to the changes seen in the study is up for debate. It may be that rats are slightly more stressed than normal – but because there of the increased social interaction and play involved, it seems to be a “good” variety of stress. Clearly more research will be needed to tease apart this interesting relationship, and to determine whether it also holds true for humans.

The research was published in the July 9, 2010 online issue of the journal Cell. Matthew J. During is affiliated with The Ohio State University.

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