Welcome back to the Nature Podcast. This week, how effective is red light therapy? And is obesity plateauing? It depends where you look. I'm Nick Petrochow. And I'm Benjamin Thompson. First up on the show, reporter Maren Huntsberger has been finding out about the science, or in some cases lack of it, behind a popular therapy. Have you seen these new red light masks? They're these slightly robotic-looking full-face masks with holes for your nose and mouth, and they shine red light onto your skin. If you believe the claims on social media, they'll help you get rid of wrinkles, reduce inflammation, treat pain, and improve sleep. Or you could get a full-body red light therapy treatment for better muscle recovery, reduced joint pain, and even slowed aging. That's what the ads say, anyway. If you're like me, you're probably feeling a little skeptical right now. And you're probably right to be. In November of last year, the UK's Advertising Standards Authority banned a number of adverts that claimed devices sold for home use could treat conditions like acne and rosacea. So is all of this red light stuff just pseudoscience? Turns out, maybe not. A recent feature article in Nature reports that there's a whole load of research going on right now, showing evidence of real, and in some cases quite dramatic, physiological effects caused by exposure to specific types of red light. I decided to speak to some of the researchers quoted in the feature and found I wasn't the only one who started off pretty skeptical of the whole thing. I was having coffee with a colleague about 20 years ago, and he said to me, I found this new method that can be neuroprotective, that can save cells from distress. And I said to him, what is it? and he goes, red light treatment, and I laughed at him. This is John Mitrofanes, a neuroscientist at the University of Grenoble Alps in France. And over the last 20 years, John has done extensive research on this topic, in particular, looking at the impact of red light on the brain. So it's been shown to be positive in animal models of Alzheimer's disease, Parkinson's disease, and aging. So this isn't just vague claims about healthier skin. This is something that could impact a serious neurological condition. But let's back up a little bit. What exactly is red light therapy? It is specific, very specific wavelengths of light that can be used to stimulate cells. And cells have receptors for this wavelength of light. And if that cell is in distress, that light will help that cell make more energy and, in essence, be healthier. Studies have found that unhealthy cells are more likely to benefit from these specific red wavelengths. The exact mechanism still isn't completely understood, but it seems to be at least partly to do with mitochondria. Those are the organelles that produce a cell's energy, and red light seems to increase the amount of energy that these mitochondria can produce. This not only has direct impacts on the cell itself, but is also thought to have systemic effects, such as affecting body parts that weren't even exposed to the light at all, or changing gene expression. This idea about the effect of light on mitochondria, and thus on wider physiology, is known more technically as photobiomodulation. And it isn't a completely new idea, but there has been a recent boom in research on this topic. Really the father of photobiomodulation, so to speak, is Andre Mester, and he was in the 60s. He used it for wound healing, and really it's kicked off since then. There's been a lot more studies looking at the actual mechanisms involved, a lot of clinical stuff, and the last five years, it's just got crazy. Some of these results are pretty well established already. Red light photobiomodulation has been recommended as a treatment for some ulcers, a kind of pattern baldness, certain types of nerve damage, and more. More recent studies also suggest possible improvements in stroke recovery, muscle recovery in athletes, retinal degeneration, and depression symptoms. And there's lots of interest in trying out red light on even more conditions. For example, one new trial proposes testing whether brief exposure to red light can improve the quality of embryos produced during IVF. Another researcher studying the therapeutic potential of red light is Juanita Anders. She's a neuroscientist at the Uniformed Services University in the U.S. who's been interested in this topic for the past 30 years. I'm a neuroscientist, basically by trade, and I looked at the literature and I came across red light therapy. And when I looked at the experiments they were all pretty bad uncontrolled And I thought I could do a much better experiment than that Her current work looks at specialized nerves called pain fibers. In my case, in the last five years, I've been using light to suppress pain using very high powers, high wattages, high irradiances with light put directly on nerves. And we have shown in the last four years that we could selectively block transmission of pain in pain fibers. In this work, researchers deliver very high intensity red light through a fiber optic cable and a needle directly to these nerves. This is a high powered setup in a carefully controlled clinical setting, so not exactly something you could try at home. And when it comes to the low-intensity red light devices you can buy for home use, Juanita is pretty skeptical about their benefits. Since we had the development of LEDs, they're very cheap. You could put them in all kinds of formats. And so there's been this explosion of devices for you name anything. put lights in your shoes, wrap it on you. And they'll all say the same thing. Oh, light can change inflammation, light can cause cell proliferation, light can increase collagen. But their device was never tested. And most of these devices, because of FDA restrictions and safety, are suboptimal. They don't have enough power to really do what they need to do. They're not going to hurt you, but will it help you? It's probably just a waste of money for a lot of them. The devices on the market are generally low power enough that they're not going to burn you if you hold them in one place for too long. But Juanita says a much higher intensity is actually what's needed for a lot of the medical treatments that her research looks into. Despite this strong skepticism, Juanita does occasionally use red light on herself. I have a therapeutic laser that is pretty high power. And I know if I want to treat deep muscle pain or back pain, I treat it myself, but it's not something I can recommend someone else to do. It's based on my knowledge of the wavelengths. It is very successful. John agrees that the wavelength and dose of the light used are key factors when it comes to home devices. Some are better quality than others. Don't buy something that's just an LED covered with a bit of red tape or something. Check the wavelengths. And if it's upwards around about 670, round about there through to the near-infrared 800s, up to 1,000, then you're in the right range. John is also convinced enough by his early results on Parkinson's and aging to be trying red light therapy on himself using a specialized helmet that he puts on for a while each day. Overall, researchers have different ideas on the best way to use red light therapy and its most useful benefits. But there is a shared hope that this surprising effect could be used to really improve people's health. So what's next? The important thing is to get proper clinical trials with proper controls. The field has been lacking that since the inception. And in terms of mechanisms, we've still got to work out the right dose. And we're working on that. And by the time I die, I'm hoping that light will be part of the discussion. In the pain world, I would really like to see it replace pharmaceuticals for pain control. I would like to see it actually be a very effective transcranial treatment for depression and for diseases, neurodegenerative diseases like Parkinson's and Huntington's. I think that these hard problems are where this field could really find an important place in our medical system. Juanita, John, and other researchers interviewed by Nature have high hopes for the future of red light therapy. But there's also a worry that the current hype around at-home devices may be giving the field a bad name. Third-party testing on some of these commercial devices has shown that many of them fall short of their advertised claims, and this may impact people's perception of the legitimate science being done. But it seems that even while much-needed research continues in the lab, probably so will use of red light therapy in many homes, even those belonging to the researchers themselves. Maren Hunsberger there, talking to Juanita Anders. You've also heard from John Mitrofarnis. To read Nature's recent feature article on the science of red light therapy, look for a link in the show notes. Coming up, researchers have done a huge analysis of obesity rates across the globe and found quite a nuanced picture. Right now though, it's time for the research highlights with Dan Fox. A DNA tool has pinpointed the origins of trafficked pangolins The scaly mammals are often poached for their meat and scales which are used in traditional medicine, but efforts to trace these illegal trade networks have been hindered by a lack of samples. To overcome this, researchers developed a technique to retrieve DNA from degraded materials and analysed more than 700 samples, including archival museum specimens and confiscated market goods. Variations in the genetic material enabled the scientists to draw a location-based DNA map for the three most trafficked pangolin species, allowing the researchers to trace the animals back to poaching hotspots as specific as a particular forest in Cameroon. The authors say that this sampling technique could be a powerful resource for law enforcement officials who can implement strategies to stop trafficking at its source. You can track down that research in PLOS Biology. A distant neighbour of Pluto turns out to have a thin atmosphere. Most bodies that orbit the Sun beyond Neptune, known as trans-Neptunian objects, are too cold to have a gassy atmosphere, with Pluto the only such object known to have one. Now though, researchers have studied a trans-Neptunian object called 2002 XV93 as it passed in front of a background star. As the body moved in front of the star, the astronomers saw the star's light gradually dim, suggesting that there is a thin layer of gas surrounding the object. At roughly 550 metres across, less than one quarter the size of Pluto, it is unclear how something as small as 2002 XV93 could hold on to an atmosphere over time. The researchers suggest that the atmosphere might have been formed recently by the release of gas from icy volcanoes or from a cosmic collision with another frozen object such as a comet. You can observe that research in Nature Astronomy. Next up, you may have heard the term obesity epidemic to describe the idea that obesity is growing worldwide. And that is generally true. But when you start to look into the details, it's not quite that straightforward. That's the topic of the next story, as there's a study in Nature this week where researchers have looked at a trove of data from hundreds of countries around the world over 40 years to try and figure out how obesity is changing. The team hope this will help them understand how some nations have curbed the trend and what could be effective elsewhere. Reporter Anand Jagatir spoke to one of the authors of the new study, Majid Azati, and started by asking him what they were interested in understanding. When we look at the global level, there has been a rise in obesity over a period of decades. So the term that people are using these days is a global epidemic of obesity. And this treats the whole world as being a relatively homogenous, uniform place. What we really wanted to do was to zoom in onto short-term changes, and especially recent changes, to say, has this changed over time? Are there some places that have controlled it, at least for every country in the world, to try to understand what's been happening to obesity, what's happening to it today? where is it heading. So could you tell us a bit more about the data that you actually collected to look at this? How granular is the data? We were looking at 200 countries around the world. We looked at the percent of population who were affected by obesity. We said, well, can we measure the velocity of change? Can we measure the speed of change? And that's what we did. We did this separately for children and adolescents and for adults. We also looked at men's and females separately and we were looking at a period of about four and a half decades from 1990 to 2024. This is an important period because it really was in the 1990s when people started to use the term epidemic of obesity. So let's talk about your findings then. So obviously you've collected data across basically the whole world over a very long time period. Maybe we could start by looking at wealthy countries. So what were some of the things that you noticed when you started to tease those apart individually? I mean, one of the first things that we realized is that there were some countries that even before we were using the term epidemic, the rise in obesity had stopped. So in Denmark, in the case of children and adolescents, around 1990, it had already plateaued around then. There were a number of other countries that children and teenagers followed them, Iceland, Switzerland, Belgium, Germany. And then we saw more of this in the case of adults, in the case of largely wealthy countries. And I should emphasize that it has plateaued in a number of countries, but it has plateaued at different levels. So here we are, we have had a few decades of places that the rise has stopped. And we haven't been telling this story until now, because we've been looking at it only over really long horizons. But there were some wealthy countries that didn't follow this trend of a rise and then a plateau in obesity. There were some countries that we could say that taken all together they didn really experience a rise in obesity and France maybe the most notable of these and then females so girls and women in Japan maybe another example of that So just to clarify then, in Japan, for women and girls, and also in France, for males and females, basically, there was no increase in obesity across the entire period that you looked at. That's correct. And I mean, let me also mention Spain. I mean, in the case of Spain, in adults, and especially adult women, it may well be the most notable example of where where the decline has begun so probably a slight decline for something about a decade and the negative side there seems to be something happening in the sort of very northern tip of europe places like sweden and finland that this plateau that you know in denmark happened decades earlier it doesn't seem to be happening there it's still going up okay so that's the picture broadly for higher income countries where for the most part apart from some exceptions obesity has gone up and then flattened off. But when you looked at low and middle income countries, the picture was very different, wasn't it? In countries that have low income and middle income countries, so this is throughout Asia, many parts of Latin America, the rise has just continued. It's continued steadily or for that matter has accelerated. And it's going up at levels of obesity, at the percent of population that's higher than many of the Western countries that we're experiencing. So there is nothing natural about this plateau. It happened in some places at moderate levels. It happened in some places at low levels, but there are places that have completely surpassed these and they are still speeding up and going up faster. So we're almost in this divided world of wealthy Western countries somehow having brought this under control, sometimes at high levels, and many low-middle-income countries accelerating or going up steadily to really high levels. It isn't just about a sort of a single global phenomenon that's happening. So why do you think that there's been a plateau in some countries but not in others? So what seems to have happened in wealthy countries is that just the general awareness of obesity has allowed people who can afford it, they can afford it in terms of their time, they can afford it in terms of material resources, to take up the message and to eat healthier things and to do exercise and to do sports and to people elsewhere in the world, those resources are less available. and these resources some of it are at the level of a family some of them are at the level of a community so the availability of healthy foods availability of fresh foods so i know that the aim of this study wasn't to try and collect data to try and understand what might be underlying the variation in countries in obesity but in the paper you do discuss that it's complicated right i mean if you just think about all of the different factors that influence what people eat what their choices are, what's available to them, how much money they have, what their attitudes to food are, how much they exercise. I mean, that just varies massively across the globe. Absolutely. I think there is a lot of complexity in relation to social, economic, technological, geographical factors. But a role of public health and a role of policy is to actually not just understand what has happened and what the complexity is, but to try to come up with ways to overcome it. So given that you've produced this more nuanced picture of obesity around the world. What do you think are the next steps in terms of how we actually try to address it effectively? One of the things that probably should happen, but you're not really focused where, is to try to understand where things really went well. So places that plateau happened early and at low levels, or for that matter, decline is happening. But I think it can be tempting to just try to understand those places. I actually think that we need to go beyond understanding, we need to actually start testing interventions. So how do we use schools? How do we use technology? How do we use social and economic welfare programs to actually make it more likely for people to eat things that are healthy? Speaking of interventions, I think the one thing that we haven't discussed, which we probably should mention, is weight loss drugs, right? I mean, that's the major thing that's happened worldwide in recent times in terms of interventions against obesity. So I'm just wondering, you know, did you pick up on that? Was there any signal within the data about that? And how do you think that those kind of drugs play into what we've been talking about? It's impossible to talk about ABC these days without talking about the weight management and weight loss drugs. They are a really exciting new development. And it's unlikely that the set of phenomenon that we have seen are affected by them. So for individual patients, for many individual patients, they have been game changers. But in the time period we were looking at the share of population using them wasn't high enough to actually be driving the patterns we're seeing. But going forward, alongside food-related interventions, we should absolutely be looking at them. Who in the population should be using them? And what effects will they have at the level that we have been looking at? Will they actually bend the curve? That was Majid Azati from Imperial College London here in the UK, talking to Anand Jagatia. For more on that story, check out the show notes for some links. And that's all for this week. If you've enjoyed the show, do let us know. You can leave a review on your podcast app of choice, or you can reach out to us on social media. We're at Nature Podcast. And, of course, we're on email too, podcast at nature.com. I'm Benjamin Thompson. And I'm Nick Petrich Howe. Thanks for listening.
