How Is Natural Killer Cell Function Boosted by Forest Bathing?
Can the aroma of wood essential oils replicate the immune-boosting effects of walking in a forest?
Studies on the effects of “forest bathing,” or shinrin-yoku in Japanese, “a traditional practice characterized by visiting a forest and breathing its air,” have found it “can induce a significant increase in the number and activity of natural killer (NK) cells” that can last as long as a month. And because natural killer cells are one of the ways our body fights cancer by killing off tumor cells, the “findings suggest that visiting forest parks may have a preventive effect on cancer generation and progression.” How? “Why did the forest environment increase human NK activity? What kind of factors in the forest environment activated human NK cells?” What is it about the forest environment?
One thought is that the boost may be related to a reduction in stress. If you measure the amount of adrenaline flowing through people’s systems, did spending time in a forest—but not in a city—lower adrenaline levels? Yes, as you can see at 0:58 in my video Why Does Forest Bathing Boost Natural Killer Cell Function?.
However, if you drip some adrenaline on human blood cells in a petri dish, there does not appear to be any effect on NK cells. The stress hormone cortisol, on the other hand, dramatically suppresses natural killer cell activity, as shown below and at 1:09 in my video. So, might being in the forest lead to less stress and less cortisol, which releases the natural killer cells under its thumb, giving us a boost?
