As the rain in April turns into the beautiful trees, shrubs, grass and flowers of May, we can see that green is good! As we sit gazing out of our window at the marvelous greenery, we wonder, “Is it better to exercise indoors in a gym or outdoors in nature? How else is green good for health?” The US Environmental Protection Agency has estimated that Americans spend 90% of their time indoors. Is this healthy? Should we heed our mothers’ advice and “Go outside and get some fresh air”?
It has been felt for a long time that getting back to nature, spending time in natural environments, had positive mental and physical effects. Being outside supposedly lowered blood pressure, decreased obesity, helped with diabetes, reduced anxiety and depression, lessened stress, and promoted physical activity while combating sedentary leisure time. Because of these effects, doctors have given out nature prescriptions, essentially encouraging patients to get outside. There is even a Japanese practice called “forest bathing” (shinrin-yoku) whereby health benefits are obtained just by sitting in nature. Is there any data to support these health claims? One study of forest bathing showed that the practice increased natural killer cells and other cancer fighting proteins. Researchers theorize that the trees emit compounds that help plants fight disease, but apparently also help humans fight cancer as well. Another study showed that exercising in natural environments reduced stress, decreased anger, lessened depression and improved energy compared to exercising indoors. A different study compared a three-hour mountain hike with walking on treadmill indoors and with sedentary activities. Mountain hiking improved a variety of psychological parameters compared to the treadmill and sitting indoors. A 2019 study looked at nearly 20,000 people in England and found that spending two hours per week in green spaces (parks or other natural environments) improved people’s health and psychological well-being. The two hours could be all at once or spread over the week. The two hours also held for those who were ill or disabled, suggesting the time in nature was the key rather the effect of healthier people outside exercising more often. It seems that exercising outside, in a natural green space, is better than indoors. Even if the data isn’t entirely true, there is no downside risk to being outside except for encountering a few raindrops now and then.
How about living near green spaces? Is there a health benefit? One study looked at the green space of Toronto. They found that people who live in areas with more trees had less hypertension, diabetes, heart attacks and stroke. They found that having 11 or more trees in a city block reduced the risk for cardiac disease. In addition, researchers looked at NASA images of the United States and categorized each county’s greenness (a measure of trees, shrubs and grass). For every 0.1 unit increase in greenness, deaths from heart disease fell by 13 deaths per 100,00 people. This was confirmed in a study from Spain. People who live near green spaces had a 16% reduction in their risk for stroke. The mechanism of benefit of green spaces may be the lower amount of air pollution and better air quality in general in these areas. Green is good!
Another type of green is good for overall health. Green leafy vegetables (for example, arugula, green beans, kale, spinach, asparagus, broccoli, zucchini) have significant health benefits. Three servings a day reduced the risk of diabetes by 13% and lowered the risk for heart disease by 24%. Now there is new information about a different green. Add avocado to the list of healthy greens. People who ate two avocados per week had a 22% lower risk for developing cardiovascular events.
How can we put all this greenness to work for us? With a Green Prescription. The prescription itself is more than just a ticket to get medication at the pharmacy. It is a contract between the doctor and the patient. With that in mind, here is your contract with your doctor and with nature, the Green Prescription:
1) Spend 120 minutes per week outdoors in nature
2) Eat 3-4 servings of green leafy vegetables per day
3) Have 2 avocados per week
Munching on an avocado and some celery sticks while hiking through the forest is optional.
