Shunali Khullar Shroff retweetledi
Trees release invisible chemicals into the air to protect themselves from bugs and disease. Turns out those same chemicals also switch on your body's cancer-fighting cells.
They're called natural killer cells. They're a type of white blood cell that patrols your bloodstream looking for cancer cells and virus-infected cells. When they find one, they punch a hole through its outer wall and inject proteins that force the cell to self-destruct from the inside. You're born with them. Unlike most of your immune system, they don't need to be "trained" on a specific threat first. They just attack anything that looks wrong.
The 50% number in this tweet comes from Dr. Qing Li at Nippon Medical School in Tokyo, who has been studying the effects of forests on the human body since 2004. His original 2007 study took 12 men on a 3-day, 2-night forest trip, walking two hours a day. Blood tests showed 11 of 12 had roughly 50% more cancer-killing cell activity afterward. A follow-up with 13 female nurses found the same thing. But the part the tweet leaves out: the boost didn't vanish when they went home. It lasted over 7 days in both groups, and in men, it was still detectable in blood work 30 days later. Li's conclusion is that one forest trip per month could keep these cells running at a higher level year-round.
The obvious next question is whether it's the forest itself or just the vacation. Li tested this directly. A separate group took a city tourist trip with the same amount of walking. No boost to killer cells. No stress hormone drop. Zero effect. Then he ran an even more controlled test: 12 men stayed in a regular Tokyo hotel room for three nights while a humidifier pumped tree oil (from Japanese cypress) into the air overnight. Their killer cells still went up. Their stress hormones still dropped. That isolates the cause to those tree chemicals, called phytoncides. Pine, cedar, and cypress trees release the most. These chemicals were found in forest air but were nearly absent in city air. A 2021 lab study showed that one of these tree chemicals directly switches on killer cells and slows colon tumor growth in mice.
The bigger picture connects these cells directly to cancer risk. An 11-year study published in The Lancet (one of the world's top medical journals) tracked 3,625 Japanese people and found that those with weaker natural killer cells developed cancer at significantly higher rates. A separate study screening for bowel cancer found that people with low killer cell levels were 7 times more likely to be diagnosed. Li's own research across all 47 regions of Japan showed that areas with less forest had higher cancer death rates for lung, breast, uterine, prostate, kidney, and colon cancers, even after accounting for differences in smoking rates and wealth.
The caveats: Li's original studies used small groups (12 and 13 people), and the regional data show a pattern but don't directly prove that forests prevent cancer. No large-scale clinical trial has confirmed that yet. But the chain is consistent: trees release chemicals, those chemicals wake up the cells in your blood that kill cancer, the effect lasts weeks, not hours, and people with more active killer cells get cancer less often.
Japan now has 65 government-certified Forest Therapy sites across the country, each tested and approved based on the physical effects they have on visitors.
All day Astronomy@forallcurious
🚨: Research suggest that just 3 days of camping in the forest can increase the production of cells that kill cancer by more than 50%.
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