Photo: Justin Sullivan/Getty Images
The Japanese practice of “Forest Bathing” is gaining popularity – and there’s actual scientific data suggesting that it could improve your health.
Have you ever spent some time in the woods and just felt refreshed afterward? Well, a new report suggests that may be more than just your imagination.
According to a series of studies led by Qing Li, an immunologist at Nippon Medical School in Tokyo, a three-day trip to the forest can raise your body’s natural “killer cell” activity, a key part of the immune system’s defense against tumors and viruses – and the boosting effect can last up to a month. Li has spent nearly two decades researching what the Japanese call “shinrin-yoku,” or “forest bathing.”
The studies were straightforward. In one, 12 healthy men in their 40s took a three-day trip to a forest in Nagano Prefecture. Each day, they walked about 2.5 kilometers, roughly a mile and a half, at an easy pace, with rest breaks whenever they wanted them. Researchers drew blood before the trip, twice during it, and again seven and 30 days after it ended. Natural killer cell activity rose significantly during the trip and stayed elevated a full month later.
Killer cells are specialized white blood cells that identify and destroy infected, cancerous, or otherwise abnormal cells in your body. They’re a critical part of your immune system’s defense against viruses and cancer.
To rule out that any trip away from routine would produce the same effect, Li ran a second version of the experiment. The same men walked the same distance, at the same pace, through a city instead of a forest. Their immune markers did not budge. A follow-up study with 13 female nurses produced similar results to the men’s forest trip, with natural killer cell activity still elevated a week after returning home from the forest.
Li’s theory centers on phytoncides, the natural compounds that pine, cedar, and cypress trees release to fend off insects and bacteria. Air samples taken during the trips confirmed higher concentrations of these compounds in the forest than in the city.
The researchers also measured lower adrenaline and noradrenaline in urine samples during the forest trips, suggesting the subjects were under less physiological stress than on an average working day. Both the drop in stress hormones and the direct exposure to phytoncides appear to play a role in the immune response, though the exact mechanism at work is still being studied.
How to make it count
The subjects in these studies were not training for anything. They walked at a comfortable pace, rested when they wanted to, and covered a modest distance each day, about a mile and a half. There was no set route, no breathing technique, and no instruction beyond being in the forest and moving through it.
These results suggest that you don’t have to be training for a marathon or climbing mountains to enjoy the benefits of simply being outside. The goal is not necessarily exertion, but unhurried time among the trees – ideally over a few days rather than a single afternoon, though even a shorter visit is worth taking if a multi-day trip is not practical. Choose a forest with real tree cover rather than an open park, walk slowly enough to notice your surroundings, and let the trip be about being there rather than covering ground.
Li's own estimate, based on how long the immune response lasted in his subjects, is that one forest visit per month is enough to keep natural killer cell activity elevated year-round. That gives a natural rhythm to plan around: a standing monthly outing rather than a single trip to check off a list.
Where to go
Any forest with substantial tree cover will do, but conifer forests, particularly pine, cedar, and cypress, match the environment used in the research most closely. Here are four national forests, one in each region of the country, that offer that kind of setting with trails suited to an unhurried pace.
In the Northeast, there are dozens of options, and rich tree cover abounds. But the White Mountain National Forest in New Hampshire has extensive pine and hemlock woods with well-marked, gentle trails. The Pinkham Notch Visitor Center is a good starting point, with several short loops nearby that stay level and shaded.
The South is also home to plenty of conifer trees, but one standout spot is Ocala National Forest in Florida. This location is home to the largest stand of sand pine scrub in the world, along with stretches of longleaf pine. The recreation areas at Juniper Springs and Alexander Springs both have easy nature trails and boardwalks, and the forest is open and walkable year-round given Florida’s mild winters. Some of the spring areas charge a day-use fee; check current rates on the Forest Service website before you go.
In the Midwest, vast stretches of forests become a little more difficult to find, but most states have at least some options. Hiawatha National Forest in Michigan’s Upper Peninsula mixes white pine, red pine, and northern white cedar. The Colwell Lake Loop, about two miles, is fully surfaced for accessibility and follows the lakeshore through the trees.
In the West, trees can become a bit more sparse, particularly in low-lying desert areas. But mountains usually mean at least some trees. Coconino National Forest in Arizona contains the largest contiguous stand of ponderosa pine in the world. Several gentle, well-marked trails start within a short drive of downtown Flagstaff, including routes through the Fort Valley area north of the city.
Because the benefit depends on repetition, the forest closest to home may matter more than the one worth flying to. Pick whichever of these fits your routine, and treat it the way you would a standing appointment.
Have you noticed a difference in how you feel after time spent in the woods? Share your experience in the comments.
Comments