shield immunity Archives - Amazing Health Advances

Forest Bathing to Boost Anticancer Immunity

The AHA! Team — Wed, 30 Jul 2025 06:38:14 +0000

Michael Greger M.D. FACLM via Nutrition Facts – Spending time in a forest, or even anticipating it, significantly lowers levels of cortisol (a stress hormone), more so than being in an urban area. Natural killer cells are one of the ways our body fights off cancer, and visiting a forest can induce a significant increase in both their numbers and their activity. I’ve previously shown how exposure to nature can have self-reported psychological benefits, but there was a dearth of data on changes in objective measurements, so I was excited to see this paper on the effects of forest bathing, “a traditional practice characterized by visiting a forest and breathing its air,” on levels of the stress hormone cortisol in the participants’ saliva. The level of cortisol in our saliva is considered an indicator of our stress level, and study participants’ salivary cortisol levels were significantly lower after walking in a forest or even just hanging out in one (“forest watching”), compared to walking or just being in a city, as you can see at 0:49 in my video Boosting Anticancer Immunity with Forest Bathing. However, the same effect was found before they went to the forest, too. Indeed, “forest bathing, in particular forest watching, was associated with significantly lower cortisol levels both before and after this practice if compared with visiting an urban area.” Therefore, it appears that just the thought of spending time in a forest relieves stress. So, “when comparing the effects of forest bathing versus urban visiting, the anticipated placebo effect…may play a more important role in influencing cortisol [stress] levels than the actual experience” of being in the forest. I was ready to dismiss this as just another nebulous psychological effect until I read this: “Studies on the effects of ‘Shinrin-yoku’ [forest bathing] on the immune function showed that visiting a forest can induce a significant increase in the number and activity of natural killer (NK) cells,” one of the ways our body fights off cancer. That got my attention. It all started with this study: Twelve men were taken on a long weekend trip to walk in the forest, and nearly all of them (11 out of 12) showed higher natural killer cell activity afterward. It wasn’t just a little increase either; they had about a 50 percent increase in NK cell activity after the trip compared to before they went to the forest, as you can see at 2:00 in my video. Now, exercise alone can affect immune function, but “there were no significant differences in walking steps before and during the trip.” The study participants were just walking in a forest instead. However, they were taken on a trip somewhere, which introduced other variables, so what about randomizing them to go on a city trip versus a forest trip? If there were some special forest effect, how long would it last? Do you have to walk in the forest every day? Before jumping into all that, let’s first see if it works in women, too. This study had the same kind of set-up, and the same kind of results: a significant boost in natural killer cell activity from walking in the woods. What’s more, this time, the participants were retested a week later, and their natural killer cell activity was still up. When they were retested a month after the trip their levels were back to baseline, as you can see at 2:45 in my video. So, walking in the woods once a week should do it, but the study involved a multi-day trip. Who can go to the forest all weekend, every weekend? How about just a day trip? The title gives it all away: “A Day Trip to a Forest Park Increases Human Natural Killer Activity and the Expression of Anti-Cancer Proteins in Male Subjects.” The same results and the same big jump measured the day after the trip compared to before and with the same staying power, as you can see at 3:08 in my video. And, natural killer cell activity was still boosted a week later. “This suggests that if people visit a suburban forest park once a week on a day trip, they may be able to maintain increased NK activity” and a boost in anticancer immune function. I’m still not convinced, though. How can you attribute the benefit to the forest itself, when all you have are before and after data? To make the case that nature had anything to do with it, you’d need a control group of study participants who took the same kind of trip but went somewhere else instead. And here we go. Again, the study title says it all: “Visiting a Forest, but Not a City, Increases Human Natural Killer Activity and Expression of Anti-Cancer Proteins.” By the end of the forest trip, the participants experienced a boost of 80 percent in NK activity after forest bathing, compared to only a 10 percent bump for the city walkers, as shown below and at 3:58 in my video. Both trips were matched for physical activity, alcohol, and sleep, too— other factors and behaviors that can affect immune function. So, we’ve got confirmation of boosted immunity, but only on the forest trip, “indicating that forest bathing does indeed enhance human NK activity.” Moreover, the researchers found that “the increased NK activity and numbers of NK cells induced by a forest bathing trip lasted more than 7 days, even 30 days, after the trip.” As you can see below and at 4:26 in my video, NK activity was still up a week later and even a bit up a month later. “This suggests that if people visit a forest once a month, they may be able to maintain increased NK activity. This may be important in health promotion and preventive medicine.” Now that we know that forest bathing induces a real effect, the next question is, Why? What is it about forests that give us the boost? (You can imagine Big Pharma wondering if it can be made into a pill.) We’ll find out next. The video I mentioned at the start is Are There Health Benefits of Spending Time in Nature?. Stay tuned for the follow-up post: Why Does Forest Bathing Boost Natural Killer Cell Function?. For other ways to improve immune function, check out related posts below. Key Takeaways Spending time in a forest, or even anticipating it, significantly lowers levels of cortisol (a stress hormone), more so than being in an urban area. Forest exposure is associated with a notable increase (around 50 percent) in NK cell activity, which plays a role in fighting off cancer. After a single forest trip, NK cell activity remains elevated for up to a week, and, in some cases, positive effects last up to a month. A day trip to the forest can be enough to maintain elevated NK cell activity if done weekly or monthly. Studies comparing forest versus city exposure confirm that forest environments uniquely boost immune function, independent of other factors like exercise and sleep. To read the original article click here.

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Immunity of Recovered COVID-19 Patients Could Cut Risk of Expanding Economic Activity

AHA Publisher — Sat, 09 May 2020 07:00:42 +0000

Georgia Institute of Technology via Newswise – While attention remains focused on the number of COVID-19 deaths and new cases, a separate statistic – the number of recovered patients – may be equally important to the goal of minimizing the pandemic’s infection rate as shelter-in-place orders are lifted. The presumed immunity of those who have recovered from the infection could allow them to safely substitute for susceptible people in certain high-contact occupations such as healthcare. Dubbed “shield immunity,” the anticipated protection against short-term reinfection could allow recovered patients to expand their interactions with infected and susceptible people, potentially reducing overall transmission rates when interactions are permitted to expand. New modeling of the virus’ behavior suggests that an intervention strategy based on shield immunity could reduce the risk of allowing the higher levels of human interaction needed to support expanded economic activity. The number of Americans infected by the novel coronavirus is likely much higher than what has been officially reported, and that could be good news for efforts to utilize their presumed immunity to protect the larger community. Serological Tests However, there are two important caveats to the strategy. The first is that the duration of immunity to reinfection by SARS-CoV-2 remains unknown; however, individuals who survived infections by related viral infections, like SARS, had persistent antibodies for approximately two years – and those who survived infection to MERS had evidence of immunity for approximately three years. The second issue is that determining on a broad scale who has antibodies that may protect them from the coronavirus will require a level of reliable serological testing not yet available in the United States. “Our model describes ways in which serological tests used to identify individuals who have been infected by and recovered from COVID-19 could help both reduce future transmission and foster increased economic engagement,” said Joshua Weitz, professor in the School of Biological Sciences and founding director of the Interdisciplinary Ph.D. in Quantitative Biosciences at the Georgia Institute of Technology. “The idea is to think in advance about how identifying recovered individuals could help serve the collective good, using information collected on neutralizing antibodies in new ways.” A paper describing the modeling behind the concept of shield immunity was published May 7 in the journal Nature Medicine by a team of researchers from Georgia Tech, Princeton University and McMaster University. The researchers studied the potential impacts of presumed immunity among recovered persons using a computational model of COVID-19 epidemiological dynamics, building upon a SEIR (susceptible-exposed-infectious-recovered) framework. In a population of 10 million citizens, for example, the model predicts that in a worst-case transmission scenario, implementation of an intermediate shielding strategy could help reduce deaths from 71,000 to 58,000, while an enhanced shielding plan could cut deaths from 71,000 to 20,000. The model also suggests that shielding could enhance the effects of social distancing strategies that may remain in place once higher levels of economic activity resume. Identification of individuals who have protective antibodies against the novel coronavirus has begun only recently. Antibody tests are not 100% specific, implying that tests can lead to false positives. However, targeted use of antibody testing in groups with elevated exposure will lead to increases in positive predictive value, even with imperfect tests. The serological antibody test differs from widespread polymerase chain reaction (PCR) testing being done to determine whether people are actively infected with the virus. Identifying Recovered Individuals Among healthcare professionals, serological testing could identify recovered individuals who might then be able to interact with patients with reduced concern for infection. Other recovered individuals could be used to help reduce transmission risk in nursing homes, the food service industry, emergency medical services, grocery stores, retailing and other essential operations. Across society, the relatively small number of individuals with immunity could substitute for people whose immunity status isn’t known; reducing transmission risk both for recovered individuals and those who remain immunologically naive. “We want to think about serology as an intervention,” Weitz said. “Finding out who is immune to the coronavirus could make a big difference in trying to reduce the risk to people who would be vulnerable by interacting with someone who could pass on the disease.” Serological testing to identify those with immunity might begin with healthcare workers, who may be more likely to have been infected by the coronavirus because of their exposure to infected persons, Weitz said. Because so many infections do not produce the distinctive COVID-19 symptoms, it’s likely that many people have recovered from the illness without knowing they’ve had had it, potentially expanding the pool of recovered persons. “There may be a deeper pool of individuals who can help within their own fields and other fields of specialization to reduce transmission,” Weitz said. “The reality is that people within high-contact jobs probably are likely to have a higher incidence of infection than other groups.” But using antibody information about individuals would create potential privacy issues, and require that those individuals make informed decisions about accepting additional risks for the greater good of the community. “What this model says is that if we could identify individuals who are immune, there is a chance that some individuals would not have to reduce their level of interaction with others because that interaction would be less risky,” he added. “Rather than trying to keep reducing interactions, which is helpful for reducing transmission but bad for what it does for the economy, we might be able to maintain interactions while reducing the risk, combined with other mitigation approaches.” Ultimately, addressing the pandemic will require development and mass production of a vaccine that could boost immunity levels beyond 60 percent in the general population. Until that is available, Weitz believes that shield immunity could become part of the approach to the challenge. “We don’t have a silver bullet,” he said. “Until we have a vaccine, we will have to use a combination of strategies to control COVID-19, and shield immunity is potentially one of them.” To read the original article click here.

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