CAGEY CONCLUSION: Stress associated with a stimulating living environment appears to protect mice from cancer, according to a new study.
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Stress is often linked to heart disease and other ailments, but a new study suggests that the strains of living in crowded and challenging physical environments might mitigate against cancer. Scientists found that simply placing mice afflicted with cancer in a more complex living environment resulted in a remarkable reduction in tumor growth.
While eating a healthy diet and reducing exposure to carcinogens are certainly important ways to reduce cancer risk, the results show that other components of the environment like an individual's surroundings, social interaction and mental state may also have profound impacts on cancer.
To examine how living conditions might affect cancer development, Matthew During of The Ohio State University Comprehensive Cancer Center and colleagues raised mice in either standard laboratory housing (five mice per cage) or in an enriched environment with more room, a greater number of mice (18 to 20 animals), and more challenges and activities (running wheels, tunnels, toys, mazes and nesting material). Mice were then injected with tumor cells, which led to malignancies in all of the control animals within 15 days. By contrast, the rate of tumor formation in animals living in the enriched environment was significantly delayed, and 15 percent had not developed tumors after nearly three weeks; when tumors were visible, they were 43 percent smaller than the lesions on control animals.
"Up front, we didn't really know whether this would be good or bad for cancer," says During, professor of molecular virology, immunology and medical genetics. "We were amazed that the effect was very pronounced," he adds. The study was published online July 8 in Cell .
The cancer resistance was not simply due to increased physical activity, however, because animals that only exercised more did not experience the same benefits. During says he suspects that the key may lie in the more diverse social encounters experienced by the mice in the enhanced environment.
"These [enriched] environments are somewhat stressful for the animals. They're not in a happy place," During says. "It's a more wild, challenging environment."
Consistent with this, the animals in the augmented setting had a slightly elevated stress hormone level as well as stronger immune systems. During noted that the most consistent and dramatic finding, however, was a nearly 90 percent drop in leptin, a hormone produced by fat that helps regulate metabolism. In humans elevated leptin levels are associated with a greater risk of some cancers, including melanoma, breast and prostate malignancies.
The scientists then traced the leptin decline to a pathway that originates in the brain's hypothalamus. They discovered that animals living in the enriched environment had higher levels of a protein called brain-derived neurotrophic factor (BDNF). To determine the role of BDNF in tumor resistance, the scientists engineered an increase in BDNF in the control mice and found that the leptin levels in the animals decreased, their immune systems were boosted, and their tumors shrank. Conversely, eliminating BDNF in the more stimulated mice blocked their lifestyle's tumor-protective effects. These experiments confirmed that the environment-induced increase of BDNF in the brain and consequent decline in leptin were causatively involved in the observed beneficial effects.
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9 Comments
Add CommentThe article heading is misleading! What the researcher deems as stressful environment for the mice is actually a setting closer to their natural habitat. How does he know what the mice were thinking ("they are not in a happy place")? How does he know that they deemed the enhanced environment stressful? IMHO this study proves that 5 mice per cage in a lab is stressful as they are the ones with more cancer! Logic would follow that the enriched environment mimics the natural, social habitat of mice resulting in happier mice. Happier mice, less chance of cancer - not more stress, less chance of cancer.
Reply | Report Abuse | Link to thisGiven an environment as indicated above, what was happening inside the mice? Were the mice stressed or challenged? Personally, I think that if the situation brought an inspired challenge to the mouse, positive results would surely come about, but if the situation brought undue stress to the mice, an opposite finding would result.
Reply | Report Abuse | Link to this@effnannie
Reply | Report Abuse | Link to this"Consistent with this, the animals in the augmented setting had a slightly elevated stress hormone level as well as stronger immune systems."
So the mice are indeed more stressed in the enriched environment. Also, it was already found that physical activity was not a major factor. And a setting with more mice would of course be more stressful, because of the increased social demands and competition.
Just wondering though, is stress entirely negatively correlated with happiness? Perhaps counter-intuitively, could one be more stressed, but at the same time happier? Then effnannie might have a point, because we would also have to know if the mice in the enriched environment were happier, albeit more stressed out.
@effnannie
Reply | Report Abuse | Link to this"Consistent with this, the animals in the augmented setting had a slightly elevated stress hormone level as well as stronger immune systems."
So the mice in the enriched environment were definitely more stressed out. And 18 mice in a cage is certain to cause greater social competition and demands, and thus more stress. I do not know how many mice are needed to ensure optimum social interaction, and thus, as you say, imitate the natural habitat of these lab mice. And you can't say that the study "proves" that the 5 mice per cage setting is clearly more stressful because of the cancer. The article just said the exact opposite, and while it seems confounding at first, if there is sufficient justification, then there is no reason to disbelieve it. You're arguing from the basis that stress does cause cancer proliferation; it seems that you have had your mind made up before even reading this article. So it wouldn't have mattered what the authors have said.
Just wondering though, is stress completely negatively correlated with happiness? Could one, perhaps counter-intuitively, be somewhat more stressed, but also happier? If the mice were indeed happier despite the challenges, then effnannie would have a point. The major factor would be happiness then (although deciding which hormones to measure would be harder than measuring stress hormones, no?)
Stress follows the Yerkes-Dodson law, which is basically the usual bell curve distribution for the optimal level of arousal for optimal performance given a particular task. On a more general physiological level, it has been well established that chronic under-stimulation of an organism's psychical and mental faculties will lead to atrophying of those systems. The body basically acts as one big efficiency machine, conserving its efforts and resources until absolutely necessary. This is why we need to regularly be "pushed" to grow in both body and mind for optimal health. (However, too much stress, such as high chronic stress, will "break" rather than atrophy these important regulatory mechanisms!)
Reply | Report Abuse | Link to thisThere is even a name for this beneficial level of stress between too little and too much--it is called "eustress." It is what gives you that little burst of urgency, focus, and motivation when you are preparing to do your best on an exam. These little mice have probably found their evolutionarily adapted sweet spot of arousal.
Also, it appears that the operational definition of "stress" in this particular study is simply one measure core measure--the concentration or circulating levels of glucocorticoids in whatever tissue or serum they were using. Glucocorticoids such as cortisol are often talked about negatively, but these steroid hormones are quite important to our normal arousal, energy, and functioning as demstrated by those who suffer from Addison's disease.
Reply | Report Abuse | Link to this"The animals in the augmented setting had a slightly elevated stress hormone level..." and certainly a constrictive response of the vessels throughout the body to elevated stress hormone level. So the question: Why is tumor growth reduced in stressed animals?"- could be answered: ..because the blood supply and oxygen delivery to the tissue is reduced, the chances for fast proliferating of the tumor cells would be slim. On the other hand, stress could accelerate ishemic cardiovascular or cerebrovascular events and led to a lethal outcome even before the tumor impact on survival becomes manifest.
Reply | Report Abuse | Link to thisThe experiment showed that social stress and other challenges increased the levels of BDNF. Removing the BDNF allowed the tumors to grow faster showing a direct cause.
Reply | Report Abuse | Link to thisMeasuring chemicals is easier than attempting to measure the happiness of mice by way of, say, facial expressions, vocalizations, or body language.
In prisons, solitary confinement is used as punishment. So, putting people in stress-free environments without stimulation is certainly a way to make us unhappy.
Other observations support the proposition that social interaction, even if stressful, allows a person to be happier than when placed in isolation. I've made the same observation in dogs, cats, and horses because I can see whether or not they're happy.
Yet, it remains to be seen if happiness itself suppresses tumor growth.
I also argue with the term "stressful" in the title. It seems logical to me that the type of stress is at least as important as its amplitude. We know about stress disorders, and know that major life events increase one's susceptibility to disease and raises the probability of death. But I find it bizarre to imagine that being in an environment that is socially "stressful" because it contains too many "good" things could have the same physiological consequences as the opposite, and I don't think it is just the eustress mentioned by stumpykat. Logic would dictate that hormonal and other chemical profiles would be drastically different--and with obviously different effect--for animals presented with a surplus of all the good things of life compared, say, to those that are being constantly chased and bitten by other animals. I think that the stress of having to choose between having lobster or having rib-eye would be different than that of having to choose which garbage can in which to go dumpster diving.
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