The more trees there are in your surroundings, the less likely you are to get cancer, according to an epidemiological study published by researchers at Nippon Medical School in the Open Public Health Journal.
We wrote recently about another study by the same authors. That was about the effect of walking in an environment with lots of trees versus running in an urban environment. Walking in a leafy area lowers blood pressure and the concentration of stress hormones in the blood more so than walking in the city, the Japanese discovered.
The researchers are studying a phenomenon known as shinrinyoku. In English publications this is translated as 'forest bathing'. As a result of the research done by the group there are now 44 forests in Japan that have been recognised as zone in which forest bathing has a positive effect on health. Thanks to the group’s work, planners have now also saved forests from urban development in Japanese cities.
The researchers suspect that trees emit certain compounds that reduce stress and activate the immune system – and thus in the long term reduce the chance of developing cancer. The substances are called phytoncides. [Immunopharmacol Immunotoxicol. 2006; 28(2): 319-33.] Plants such as oak, fir trees, but also tea bushes and onions, emit these substances to protect themselves against insects, animals and microorganisms. About five thousand phytoncides have been identified; and probably all living plants produce them.
The researchers succeeded in showing that there were raised concentrations of a number of phytoncides in Japanese forests, including alphapinene, beta-pinene, tricyclene, camphene and d-limonene.
In the study that was published in 2008 in the Open Public Health Journal, the researchers collected data on cancer-related deaths in Japan. They looked at the data for each province and corrected for smoking and income. They then looked at the area of forest in each of the provinces, and so discovered that death from cancer was lower the greater the amount of forested area there was in a province.
The researchers found statistically significant effects for lung and breast cancer in women, and in men for prostate cancer, gut and kidney cancer. The figure below shows the relationship between forested area and breast and prostate cancer.
"Forests may partially contribute to decreased SMR of some cancers in Japan", the researchers conclude.
The Open Public Health Journal, 2008, 1, 1-7.