无论你是狂热的背包客，还是喜欢偶尔去公园散步的人，又或者是与大自然的关系介于两者之间，可能都已经感受过大自然带来的“神奇”减压效果。与之相关的“公园20分钟效应”虽然是最近才火起来的，但实际上，早在40年前科学家就发现，这种现象不仅有助于放松身心，还可以加快手术恢复速度。1984年，《科学》（Science）上的一项研究发现，相比窗户面对砖墙，病房窗户可以看到自然景观的患者术后住院时间更短，护士记录中收到的负面评价更少，且使用的强效镇痛药也更少。这些患者身处同一家医院、同一种病房、接受着同一种治疗，他们的术后恢复和健康状况难道仅会因为看到的景色不同而产生差异吗？英国牛津大学（University of Oxford）圣艾德蒙学院（St Edmund Hall）院长、生物多样性教授凯西·威利斯（Kathy Willis）表示，自然对人的影响是全方位的：这既体现在我们可以在户外和室内与植物建立联系，也体现在自然可以通过人的多种感官发挥作用，包括视觉、听觉、嗅觉、触觉，以及一个隐藏的感官，它们都可以接收自然发出的信号，并由此调节我们的健康状态。总体而言，与自然互动的过程会直接触发我们体内三类不同的反应。首先是神经系统，它引发了一系列生理活动的改变，如呼吸频率变化，心跳减慢，血压降低，心率变异性（HRV）提高（HRV的升高表明心脏具有更高的适应能力）等。这些生理指标的变化代表一个人正在变得更放松。同时，接触大自然也会影响我们的激素分泌。比如，与自然互动时，人的肾上腺素水平会下降、唾液淀粉酶活性会变高，这与短期内的压力降低有关。众多心理学实验也表明，当人的感官与自然界的某些元素相互作用时，心理状态会得到改善。其次是那个隐藏感官，也就是肠道。威利斯表示，生物多样性更丰富的自然环境中也含有更多样化的细菌群落，当人们置身其中，身体会适应并移植一些益生菌到体内，触发各种对身体有好处的代谢过程。网上经常有文章称“我们必须每周摄入30种植物”、“多吃腌菜以增加肠道微生物群多样性”等。威利斯说，这确实有道理，其中蕴含了许多非常重要的科学知识。比如高达93%的肠道微生物并非通过遗传先天所得，它与我们的环境及饮食息息相关。如今，我们非常重视饮食，却忽视了环境的影响。近十年来，大量研究开始揭示，在一些生物多样性更丰富的天然环境中，在植物种类繁多、高低错落，化肥没有被滥用的地方，环境空气会充满各种细菌。如果我们身处其中，接触到有机的土壤，就可以将这些细菌摄入体内，让它们定植在肠道上，更好地利用其中的有益成分。2020年发表于《科学进展》（Science Advances）的一项研究也证实了这一观点。研究人员在芬兰的日托班面向幼儿园年龄段的儿童开展了一项对照实验。他们将小朋友们分为两组，一组在装有当地松树林土壤的沙坑中玩耍，另一组则在无菌沙子填充的沙坑中玩耍。研究人员测定了这些孩子的皮肤微生物群和肠道微生物群，以及血液中的免疫生物标志物。28天后，他们发现，在林地土壤中玩耍的孩子肠道内的微生物群显著增加，他们血液中的炎症标志物也显著降低。研究人员后续还在成年人中发现了同样的现象，不论是去山里玩泥巴还是在家里养植物，28天后他们的肠道菌群也发生了类似的变化，对他们的血液产生了积极的影响。因此，除了在饮食上多加注意，多去大自然里走走、和植物“玩耍”、接触森林中的土壤也有利于培养健康的肠道菌群。考虑到许多人正在城市打拼，他们被困在办公楼和钢筋水泥组成的“城市森林”中，接触到可以放肆玩耍的土壤或郁郁葱葱的绿地可能没那么容易。面对这种情况，威利斯也指出了在室内养些植物的好处。在办公室、工位和家里摆一些植物，它们就会将良好的微生物群播撒到空气中。从植物种类上看，不必以量取胜，也不必买那种昂贵的、巨大的异国情调植物，仅需一些吊兰、绿萝这种简单的花草即可，它们长得快、好养活，也能传播一些益生菌。最后，自然界对人体的影响还会体现在嗅觉和循环系统中。空气中的气味实际上是一些挥发性有机分子，它们会从植物里释放到空气中，被我们吸入鼻腔，穿过肺泡，进入血液。我们都知道空气中的污染物会通过这种途径进入血液，但来自大自然空气里的有益分子同样也会走上这条路。在血液中，这些分子会与某些生化途径相互作用，效果堪比服药。以室内植物为例，一些研究表明，当你闻到某些植物的香味时，它会通过影响体内的生化作用改变你的状态。比如，薰衣草释放的气味分子进入血液后可以起到类似于抗焦虑药物的效果，能让你更加放松。如果你想保持清醒，那就去试试迷迭香。
某些植物的气味还可以真正促进生理健康。2024年发表于肿瘤学期刊《肿瘤靶标》（Oncotarget）的一项研究表明，柏科植物的香气不仅能降低人体的肾上腺素水平，还能提升抗癌和……[查看全文]
Nature Affects Our Hormones and Changes Our Microbiome
Rachel Feltman: Happy new year, listeners! For Scientific American’s Science Quickly, this is Rachel Feltman.Whether you’re an avid backpacker, an occasional park stroller or someone whose relationship with the great outdoors falls somewhere in the middle, you probably already know that spending time in nature is a great way to de-stress. But what if leaf peeping could do more than just help you unwind? Well, according to a recent book, the sights, sounds and smells of plant life can have serious impacts on our bodies.My guest today is Kathy Willis, a professor of biodiversity at the University of Oxford, where she also serves as principal of St Edmund Hall. She’s the author of Good Nature: Why Seeing, Smelling, Hearing, and Touching Plants is Good for Our Health.Thank you so much for joining us today.Kathy Willis: It’s a pleasure, absolute pleasure.Feltman: So you’re a professor of biodiversity, and a lot of your work focuses on the well-being of plants and their ecosystems. How did you become interested in how plant life impacts human health and wellness as well?Willis: So that’s right: I’m very much someone who’s always worked at the sort of interface between looking at vegetation and climate change and—very academic. But then I was working on a big international project and they asked me to—part of my role was to pull together the information about the relationship between nature and human health.And as I was trawling through the literature I kept coming across this study published in 1984 in this journal, the top scientific journal, showing that people who looked out of hospital window beds onto trees recovered from gallbladder operations much faster and took less pain relief than those who didn’t. And I thought, “This is really strange.” So people looking on brick walls—how does that work? They’re in a chamber. They’re in a sort of a, you know, a hospital room, so it’s not anything to do with the environment of the room; it was to do with them looking on to something. Was it influencing their health?And so that started me on a very different pathway because I started to look at this paper and realizing that, very clearly, the action of looking at nature was triggering not just mental changes but physiological changes in the body that was improving these recovery rates and effects for human health. And that’s how I started the whole journey of really saying, “Well, what else is there out there? What are the senses, when you interact with nature, [that] have an impact on our health and well-being?”Feltman: That’s fascinating, and your new book, you know, examines how those senses connect us with nature. Can you tell us a little bit about what you found when you went exploring? What does the research say about how we connect to plants and the outdoors?Willis: So it’s both outdoors and indoors, but I’ll start—I can certainly start with outdoors. I mean, so the way I looked at it and the way I started to pull the literature together was looking at the different senses: so our sight, our sound, our smell, our touch, and then there’s a hidden sense, but we’ll talk about that later.But what I found, actually, is that—very much that each of these triggers these different actions in our body, and there are three sort of mechanisms that get triggered when we interact with nature: the three direct ones.But the first one is: it affects our nervous system. So it triggers changes in things like our breathing rate, our heartbeat goes down, our blood pressure goes down, our heart rate variability: it changes to a parasympathetic variability, which is—induces much more physiological calming. But it also affects our hormone system. So you can think about—I mean, I think, for me, it’s more obvious about the heart rate and the breathing, but for example, your adrenaline goes down.Willis: Salivary amylase, which is a hormone that you get in your saliva, which is elevated when you’re stressed, that reduces. And then the—all these psychological experiments show that your psychological state is better when your senses interact with certain aspects of nature.And then there are two other aspects of nature. The first is that when we breathe in the scents, those scents that you get are molecules—they are volatile organic molecules—and they basically become, they become a gas when they come out into the air from the plant. Those molecules pass into our blood. And once across our lung membrane and once in our blood, they interact with certain biochemical pathways in the same way as if you’re taking a prescription drug.And then finally, the other things—and our body takes on those aspects of nature, and it comes inside our body. And actually, we shouldn’t be surprised about that; we know pollution gets into our blood—pollution in the air gets into our blood. But so, so do the good aspects of nature. And finally, what I also found out from looking at this research is that when you’re in a more biodiverse environment, that environment has a much more biodiverse bacterial assembly—the good microbes that we all need—and your body adopts and takes on the signature of that environmental microbiome, which I find, again, fascinating. And as a result of that it triggers all sorts of metabolic processes that are good for us.Feltman: Very cool. And I would love to hear more about that hidden sense you mentioned.Willis: So with the hidden sense, I mean, you know, with—we’re constantly being bombarded—I don’t know [if it’s] the same for you [laughs], but I, every time I open the newspaper here, I see another thing about how we must eat 30 plants a week and we should eat pickled vegetables and everything else to increase your gut microbiome. And that is true. I think there’s a lot of real very, very important science in there.But what I learnt from looking at this is, first of all, that up to 93 percent of our gut microbiome is not inherited; it’s to do with our environment and what we eat. Now, we think about what we eat, but we don’t think about our environment. But a lot of work started about 10 years ago where they started to show that people that live in a more biodiverse environment—where you’ve got greater diversity of plants, different heights of plants, etcetera, etcetera—and more organic environments, so not using whole loads of fertilizers, that those environments, if you measure the air in those environments, they’re full of all these bacteria that we’re busily [laughs] chomping our way on, you know, food to try and get into our gut. And once we’re in those environments or we’re touching that organic soil, we adopt the signature, so we adopt all those good microbes, and it gets into our guts.Now why is that important? Because then there’s a very—some beautiful study’s been carried out on kindergarten-age—so, you know, children go to nursery school, or play school, in Finland where they, basically, they, for 28 days, they—one group played in a sandpit [where] they poured in soil from the, the local pine forest, and the other group had sterile sand. And they measured their skin microbiota, they measured their gut—so through their poop—but then they also measured their bloods. And what they found was that after 28 days those that had played in the soil had this hugely elevated microbiome in their gut.But the really critical thing in there is they measured their inflammatory markers in their bloods, and their inflammatory markers were right down. And they found the same with adults, adults playing with soil or adults even sitting in a room with a green wall: after 28 days they’d adopted that microbiome. But also, it’s affecting their bloods in a really good way. In the same way as we’re being told our diet—we ought to, with our diet, you know, eat more plants because it will do this—you can do that with your environment as well.And I find that really, really fascinating. So as well as eating 30 plants a week we should be interacting with the plants daily in order to build up good bacteria in our gut.Feltman: That’s really striking research, and I think it’s a great segue to—you know, many of our listeners might not have easy access to soil to play in or lush green spaces. What does the research say about harnessing those positive powers of plants in the outdoors when we’re stuck indoors or in urban environments?Willis: You can absolutely do it indoors. And I—it’s transformed the way I—my offices and where I work and even my home because what it’s shown [is] if you have plants in your office, you get all the benefits. For example, having a, a vase of roses on your desk.But on top of that plants in the room will seed the air with the good microbiota. And so something as simple as a spider plant—it doesn’t have to be something exotic and large; it can be a—something that reproduces rapidly like the spider plants. They’ve shown that those actively seed the air with this good microbiome.But then again, indoors, there’s some beautiful studies showing that when you smell certain plant scents it affects how you are. So lavender makes you more relaxed because it—once it’s in your blood it interacts with the biochemical pathways as if you’re taking an antianxiety drug. So if you want to be more relaxed or want to go to sleep, you can diffuse lavender in your bedroom. If you want to be more awake, you should have rosemary.And if you want to really do something that’s good for you, what they’ve shown is that the Cupressaceae family, when you smell that, not only does it decrease your adrenaline hormone, but it also elevates the natural killer cells in your blood...[full transcript]
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