Specifically, he studies natural killer immune cells, called NK cells, which protect us from disease agents and can, like cortisol and hemoglobin, be reliably measured in a laboratory. A type of white blood cell, they’re handy to have around, since they send self-destruct messages to tumors and virus-infected cells. It’s been known for a long time that factors like stress, aging, and pesticides can reduce your NK count, at least temporarily. So, Li wondered, if nature reduces stress, could it also increase your NK cells and thereby help you fight infections and cancer? To find out, Li brought
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