The healing power of sunlight

Could sunlight help treat disease? A growing number of studies find potential benefits of UV light therapy for conditions like multiple sclerosis, Type 1 diabetes and Crohn’s disease.

Prue Hart, professor at the University of Western Australia located at the Kids Research Institute in Perth. Her research focuses on the effects of ultraviolet radiation and vitamin D on the immune system.

Dr. Richard Weller, professor of Medical Dermatology at the University of Edinburgh

Dr. Veena Vanchinathan, Board-certified dermatologist in the San Francisco Bay Area.

Part I

MEGHNA CHAKRABARTI: Imagine you're stepping outside on a bright and sunny day. What do you feel? Maybe the rays are warm and comforting on your skin. Maybe you tilt your head back, close your eyes, and see bright spots behind your eyelids. Maybe the sun is helping you feel happy and energized.

The sun's ray can have a profound effect on our bodies. According to a growing amount of research, sunlight kicks off an array of complex biological processes. It impacts our skin, of course, but it can also alter our nervous systems or our lymph and organs, it can slow down our immune response and lower blood pressure.

But could sunlight actually help treat disease? Studies have found potential benefits of light therapy for conditions like multiple sclerosis, Type 1 diabetes and Crohn's disease. And so that's what we're looking at today, harnessing the health secrets of the sun. And we're going to start today with Prue Hart.

She's a professor at the Western, excuse me, the University of Western Australia, located at the Kids Research Institute in Perth, and her research focuses on the effects of ultraviolet radiation and vitamin D on the immune system. And she joins us from Perth, Australia. Professor Hart, welcome to On Point.

PRUE HART: Thank you. Very happy to speak to you.

CHAKRABARTI: Before we dive into the actual science of what sunlight does to the skin, it occurs to me that since I'm speaking to you and you're in Australia, one of the most sort of sun-drenched places in the world. Is that what got you interested in studying the effects of ultraviolet violet radiation?

What's the story behind your the thrust of your research?

HART: Look I grew up in sunny country. Yes, we grew up thinking sun must be bad for you and bad for your skin. But I think we are all learning now that the harm benefits of the sun are really only at the skin level. The benefits of sun is really the whole-body effects.

The benefits of sun is really the whole-body effects.

Prue Hart

And so I think we've got to consider harm versus benefit and just in the last few years that equation, the benefit is starting to outweigh the harm. Yes, you can get skin cancers, melanoma's the one you have to be worried about. And we can get, our skin ages, obviously, we get a few more wrinkles, but hopefully in this session we'll develop more about the benefits, which really are so important for our human health.

CHAKRABARTI: So what are some of the benefits that research is starting to show of the effect of sunlight on the human body below the skin level?

HART: I'm an immunologist, so I'm obviously interested in the autoimmune diseases or any diseases with an inflammatory component.

And we know, in fact, most human diseases have an inflammatory component. We know that sunlight, particularly the UVB rays of sunlight, can dampen inflammation, whole body inflammation. We know that it also can reduce stress. We know that sunlight has another, a prong by stimulating adaption in the skin.

We know that sunlight, particularly the UVB rays of sunlight, can dampen inflammation, whole body inflammation. We know that it also can reduce stress.

Prue Hart

So we learn to cope better with sunlight. Of course, as your introduction started off, we feel better too. So there's just many ways sunlight is helping us, but I talked about immunology and immunological diseases, autoimmune diseases. But I think Richard Weller is going to talk about cardiovascular diseases where sunlight can help.

We know of bone and musculoskeletal health, that was known many decades ago with the advent of discovering vitamin D, but also our neuro system, our endocrine system, our metabolic system, even our eye system, our oculus system. We know myopia is related to children being outside and having more sunlight exposure.

So really the whole-body benefits from sunlight exposure. So we've got to stop this exaggerated fear of skin cancers and think of some of the benefits and the positive aspects of sunlight.

We've got to stop this exaggerated fear of skin cancers and think of some of the benefits and the positive aspects of sunlight.

Prue Hart

CHAKRABARTI: So I want to, let's take some of these just one by one, but first of all, but before we do that, I've been generically saying sunlight.

Is that really what we're talking about, or are we talking about UV and specifically UVB?

HART: Sunlight's very complex. UV is the highest energy component of sunlight. It's the area where I've been studying. We know of the benefits from UV, but there are benefits of other aspects too. We know about blue light in our circadian setting, our circadian rhythm. We know about infrared light at the other end of the visible spectrum.

It can help in repair, it can help in heating the body. It's a whole package in a way. The sun, the benefits of sunlight. But we've evolved this way. We've evolved to get the benefits of sunlight. So not to take advantage of it, to stay inside, is not natural. We didn't evolve that way. We didn't lose pigment in our skin for a reason, not to harness the benefits of sunlight.

We've evolved to get the benefits of sunlight. So not to take advantage of it, to stay inside, is not natural.

Prue Hart

But UVB is the highest energy area of sunlight, and that's the one we harvest in our treatment of autoimmune diseases, try and dampen those hyperactive conditions.

CHAKRABARTI: Okay. This is really interesting because again, as you said, sunlight is complex. There's the visible spectrum portion of it, of course, infrared and UV.

So I'm going to come back to that in a second, but tell me a little bit more about what is happening as far as we know at the cellular level. Let's take autoimmune diseases. So with immune dampening at the cellular level, when we are exposed to sunlight, how does it actually dampen the immune response?

Yeah, go ahead.

HART: We know the skin is a very dynamic and complex organ. It covers our whole body. It's the first line of defense against environmental stresses such as UV. Now we know that the UV photons have a lot of energy. I said they're shorter wavelengths, they're high energy, and we've got cells and molecules in the skin that can absorb that energy and that energy then breaks molecules, changes molecules or chemicals in the skin, and then we get signals going from the skin down to the lymph nodes and into our blood and into our circulation.

And it's not only molecules, but cells themselves can migrate in and out of the skin. As I said, it's a very dynamic organ and we have not only, we have a lot of immune cells and that's probably the greater network that's at play.

In our dampening of things like multiple sclerosis, but we also have the endocrine system in the skin. We know a lot is happening. It'd be naive to think that there was only one system happening in the skin. It really is many processes interacting with each other and then sending signals around the body.

So the skin is really like causing body-wide communication. It's a very complex organ, but you can appreciate it's so important because it's our first line defense to stresses, environmental stresses.

CHAKRABARTI: So I definitely agree with you that there are multiple things happening in an organ as complex as the skin.

But the reason why I'm asking for more specificity about what UVB actually is doing to help produce this immune response or this dampening of immune response is because most people, when they think of ultraviolet and the body, maybe if we've heard anything about it beyond the potential for skin cancer, people have heard the skin cancer is caused because the UV damages the DNA inside your skin cells.

So what is happening that's actually positive inside some of the cells or whatever system you want to point to, that's actually changing it in a healthful way?

HART: But this is the whole point. We, our bodies, if we reacted to every sort of DNA break in our skin, we wouldn't survive.

We, our bodies, if we reacted to every sort of DNA break in our skin, we wouldn't survive.

Prue Hart

We have inbuilt mechanisms; we have innate immunity, where the skin has adapted to be able to cope with the initiation of what might progress to a skin cancer. We know that we don't react against it. Because otherwise we'd be responding to everything that comes and hits the skin.

Remember bugs and viruses and scratches and all those insults of the skin, it's the same thing. We can't react to them all. We've got to dampen down our responses. So we can evolve to be in survival mode. So it's part of saying, look, the immune system, we don't want to respond. We don't want to be, have a crash and burn response.

We've really got to calm it down. And that's what we are harnessing then in treating autoimmunity. Because we know autoimmune diseases are when the body is reacting against self, and it's usually by your immune cells. Your immune cells are destroying the body. And in the case of multiple sclerosis, it's destroying the myelin sheath around nerves.

So we've got to calm down those immune cells and say, 'Hold on, stop it.' So right at the skin level, we start developing regulatory mechanisms rather than reactive mechanisms. So if we can modify, and that's, it's all initiated or started first in the skin. And then systemically we are calming down, where there's homeostasis needed.

Part II

CHAKRABARTI: Professor Hart, if I may, you're going to have to forgive me for asking a question repeatedly, but I really do want to know in more scientific detail what we do know so far, what might be happening at the level of cells when skin is exposed to sunlight. For example, I'm reading here in the Scientific Press that says some researchers are tracking the way molecules in the skin, such as urocanic acid or lumisterol affect immune system activity.

Are these areas that you're studying and what are these chemicals?

HART: Yes. Urocanic acid was first identified, oh, 40 years ago. As a molecule in the outer layers of the skin and when it absorbs UVB photons, it isomerizes from, transforms one molecular form or chemical form to another, and it's made more soluble by this transformation.

When it's more soluble, it can then go through the skin and to our circulation and is eventually measured in the urine. Now it is a well known immunosuppressant molecule. We believe it affects antigen presenting cells, but many immune cells. So it's a molecule that has quite potentially a therapeutic benefit if it was given. The other one, lumisterol is a product from vitamin D.

Now, I think all your listeners will know about vitamin D. It is one of the molecules in skin. It's precursor when it absorbs those UVB photons, that's 7-Dehydrocholesterol. When it absorbs the UVB photons, it converts to vitamin D and then goes to the kidneys and to the liver where it's converted into the fully active molecule of vitamin D.

Now we know vitamin D, that may be important. We do not believe it really is a very important molecule because trials of supplementation with vitamin D have suggested it is a small player relative to all the other molecules that may be made in the skin. And this is why it's a very exciting area of research.

The skin, as I said, is so dynamic. It's so active. It's got so many pathways stimulating each other, feeding on each other, to send signals to different parts of the body.

CHAKRABARTI: Yeah. Professor Hart, stand by for just a moment. That's Prue Hart. You're listening to her from Perth, Australia. Let's go to basically the other side of planet Earth to Edinburgh, Scotland, where Dr. Richard Weller joins us. He's a professor of medical dermatology at the University of Edinburgh. Dr. Weller, welcome to On Point.

RICHARD WELLER: Hi. Great to be here.

CHAKRABARTI: How sunny is it in Scotland today?

WELLER: Not. Look in Scottish terms. It's sunny. We've got a UV index of 4. I used to work in Australia actually, up in Queensland, so midwinter, in, so mid-June around the middle of the day in Queensland where I was working, the UV index is 7, it rises to 14 in summer last year. Here in Scotland, the UV index hit 7 for five minutes on the 24th of June, if you're interested. And yet ridiculously, we copy sunlight advice from Australia, completely irrelevant and more than irrelevant, actually harmful.

But we can discuss that.

CHAKRABARTI: Yeah. Both of you're very keen to push back on the sort of accepted dermatological advice of protecting yourself from the sun. And I promise you, I will let both of you have your say about that a little bit later in the show. But as you can tell, I hope you can tell I'm very keenly interested in trying to understand the mechanisms that are behind this suggestion that increased amounts of sunlight do amazing things for our overall health and not just for like our emotional wellbeing.

Dr. Weller, you're in Edinburgh, it's a pretty high latitude city on planet Earth. I've been seeing that there is actually some correlation between disease incidents and literally the latitude that you are at on the planet, vis-a-vis the amount of sun that you get. Is that true?

WELLER: Yes, it is. And look, the first thing, look, the first thing doctors should do when talking about, why are we concerned about cigarettes? Because cigarettes shorten life. It's about four minutes per cigarette. Why are we worried about high blood pressure? Because high blood pressure shortens life. Why are we worried about poverty? Poverty shortens life. What about sunlight? Actually, what the studies from up here in Northern Europe show, and this is studies from Sweden and it's studies from here in the UK, they show that the more sunlight people get, the longer they live.

Because this equation, the bad side of sunlight, skin cancer, the good side, reductions in heart disease, cancer. Which of those is more important? Actually, all-cause mortality, death from any cause, is the mathematical, it's the sum of those two things. And certainly, in Northern Europe, the more sunlight people get, the longer they live. So if you are telling people to avoid sunlight, you really need to be saying why.

In Northern Europe, the more sunlight people get, the longer they live. So if you are telling people to avoid sunlight, you really need to be saying why.

Richard Weller

CHAKRABARTI: Okay. And so the why, we'll come back to. But Professor Hart, I wanted to hear you on this as well. So that just to be clear, there is a body of evidence that shows that people who live further from the equator, so therefore their exposure to sunlight is much more variable depending on the season.

That people living further from the equator tend to have a higher prevalence of some diseases. Is that true, Professor Hart?

HART: Yes. Certainly, in the autoimmune diseases. In fact, any disease with an inflammatory component. I talk about Type 1 diabetes, Crohn's disease. Richard will talk about cardiovascular disease.

So really any disease with this inflammatory component that can be dampened by UV, there will be a latitude gradient. There'll be a seasonal effect. Yes.

CHAKRABARTI: Wow. And for this to actually have like scientific salience, it has to be on basically on a population level, right? We're not talking about individual cases, right?

We're talking about overall.

HART: It's population level because we know that the environment by your genetics can combine to determine disease. But environment is a large component, and that's where the latitude gradient comes in.

CHAKRABARTI: Okay. So Dr. Weller, Professor Hart earlier had talked, she's talked about repeatedly autoimmune disorders and the impact that sunlight might have on the immune system cardiovascular health.

Can you tell me more about that?

WELLER: Yeah, so look, cardiovascular health, a big effect of sunlight. So if you are male in Scotland, but I think it also applies to females, you are 30% more likely to drop dead in a week in January than a week in July. So look, it's August at the moment.

I'm pretty mellow, safe time of year, I start to get a bit antsy towards the end of the year. This seasonal variation in disease is such, it's so built into us as the norm. If you are a doctor, it is really busy in winter and there's a kind of unspoken rule that you don't take holidays in winter, because you're all really busy.

It's not a formal rule, it's just part of the culture. And we know that blood pressure very much varies by latitude. So the further people live away from the equator, the higher average blood pressure is. And with that, we have higher rates of stroke and heart attacks.

And then work that I've done with colleagues in Germany have also done and reproduced shows that sunlight releases this substance, nitric oxide from the skin. So when you are in the sun, NOs release from your skin. And what that does is it dilates blood vessels and lowers blood pressure, and that accounts for this huge seasonal and latitudinal variation in blood pressure. And with it, heart disease.

CHAKRABARTI: ... Yeah. Oh, because I was just going to ask you, because heart disease is also one of those highly complex diseases. Where you have to talk about diet and thing and things like that as well, but you're at least seeing this very strong correlation between nitrous oxide and blood pressure though.

So that's significant.

WELLER: Yeah, look, so we've done experiments. I did a TED Talk some years ago if people want to see it. And we've very clearly shown that shining UV at people releases NO from the skin and it dilates blood vessels. And then we've done big observational studies in America actually looking at dialysis patients because they get their blood pressure measured three times a week when they get dialysis.

And we show that these 2,000 centers around America with different amounts of UV and temperature. And again, very clearly, we show that the more UV people are exposed to, the lower blood pressure is, but really about half of this effect is due to temperature. But about a half is just due to UV. And another important thing in this is that Black Americans get less of a fall in their blood pressure for a given rise in UV than white Americans.

And of course, high blood pressure, strokes, heart attacks. Are particularly prevalent in Black Americans compared to white Americans. And skin color is all about handling sunlight. That's why pale skin developed as we moved away from Africa, where we all come from. And as people moved into low light environments, they develop pale skin just to soak up more of that sunlight that we need.

And one of the things that it affects is blood pressure.

CHAKRABARTI: Okay so tell me a little bit more about, is it melanin specifically that we're talking about here? Because that's the thing that provides the visual cue of skin color. But does that have, is that part of the UV system you're talking about?

WELLER: Yeah, we don't know. All we know is that, so we know looking at our African ancestors, that white skin within Africa, before humans left Africa, we know that pale skin colors were actively selected against. You can see this in the genetic patterns of skin pigmentation.

But having moved to low light environments really quite recently, in the last 5,000 to 8,000 years only, and we've been out of Africa for about 60,000 years, there was then this really very strong selective pressure over the last 8,000 years for pale skin in Northern Europe, and response to sunlight is determined by skin color. UV induced skin cancer is purely a disease of white skinned, North European heritage people. And, but at the same time, there is less of that healthy fall in blood pressure with darker skin types, less rise in vitamin D, which is a good biomarker for biological effects of sunlight.

Skin color gives us an indication that sunlight has to have benefits. Because repeatedly as people have moved to low light environments, pale skin has developed to try and make up for that lack of sunlight.

CHAKRABARTI: Interesting. Professor Hart, did you want to add to that?

HART: I'd like to just say I support everything there. I agree that we've evolved so that we can get the benefits of sun. The paler skin allows more of the photons to hit the important cells in the skin without the melanin barrier.

But I'd also just like to add that this observational study of, as people live higher from the equator at higher latitudes, as populations. There are other studies that send the same message. There's a lot of cohort studies that have been performed around the world, so cohort studies is where people study 50,000 people or that sort of number, and usually the healthier people are those with skin cancers.

So that is telling us, yes, the skin is reacting and developing some skin cancers, some usually non-melanoma skin cancers, but they're healthier. Their cardiovascular health is better, and that's also sending us a message, that's just from natural observations.

CHAKRABARTI: Yeah. Can I come back to something about vitamin D. Because I've failed to I think understand completely what both of what you were saying. And actually Dr. Weller, let me turn to you on this. People take a lot of vitamin D supplements, and as I think Professor Hart said earlier, that in and of itself may not actually be doing you any good. That it's vitamin D produced, what, out of the skin by exposure to sunlight. That's actually the beneficial one.

Can you give me your take on that?

WELLER: Yeah, no. Look sunlight hitting the skin makes vitamin D. So measured vitamin D in your blood tells you how much sunlight you've been exposed to. We know that people with high measured vitamin D in their blood are healthier in every way. You can say less heart disease, less cancer, less diabetes, less obese, live longer, et cetera, et cetera.

The problem is when you give, correlation is not causation, is the classic thing when you give people vitamin D supplements. And in America, you ran this huge study called the VITAL study run out of Boston. 25,000 Americans given, half of them given vitamin D for five years, half given a placebo.

They didn't know which it was, all the results reported in the New England Journal. And basically, it came out vitamin D does pretty much nothing. There was some reduction in some autoimmune diseases and that was it. Now that is a huge study and the results came back negative. So what this is telling us is it's not the vitamin D, it's something else.

Vitamin D is a marker for sunlight exposure. And the problem with the debate for the last hundred years is that it's been dominated by dermatologists saying, oh, sunlight will call skin cancer. Terrible. And any benefits can be reproduced by taking Vitamin D, and that's wrong. Vitamin D prevents rickets.

But very clearly, in a great editorial in the New England Journal about two years ago, 30% of Americans over the age of 60 take vitamin D supplements. And other than rickets and a few little fringe autoimmune disease, it doesn't do much. It's not the vitamin D, it's the sunlight.

Part III

CHAKRABARTI: Professor Hart, we had mentioned multiple sclerosis a couple of times here, and I just wanted to quickly ask you about some data that has been coming out over several years from Australia itself because huge country, lots of different latitudes. So variable sunlight exposure within Australia itself.

Excellent medical record keeping. And I'm seeing here that there have been several studies that show a correlation between the incidents of multiple sclerosis and the latitude at which various Australians live. It's a fairly strong correlation and that feels quite remarkable to me. Professor Hart?

HART: I think this is wonderful data. It shows quite clearly that in the southern parts of Australia, such as Hobart, there is five to sevenfold greater prevalence of multiple sclerosis than up in North Queensland, near the tropics. So I think this is really, it's happening naturally. It's showing us that it's a real thing.

That the UV exposure, sunlight exposure, can actually dampen the initiation, the progression, the development of multiple sclerosis, such that if you get exposure to less UV down in the southern parts of Australia, you have more disease. And we've taken this a step further.

CHAKRABARTI: Oh. I was just going to ask you about that because my first question that came up when I was reading about these sort of population wide studies in Australia, was correlation doesn't equal causation.

There may be other things going on at different latitudes in Australia, but you did follow up research in a much more controlled manner. Can you tell me about that?

HART: We've done a study giving narrowband UVB to patients with the earliest form of MS. Now this was important, because we know dermatologists give narrowband UVB to treat skin conditions, we were trying to give it to patients with such that it had internal benefits. And it was not difficult to get through ethics committees, because it's so safe to give narrowband UVB.

It's wavelengths of UVB that have had no effect on skin cancer induction at all.

So we did a study of 20 patients, 10 got the narrowband UVB. 10 did not.

CHAKRABARTI: With the light box.

HART: With a light box, three times a week for eight weeks. And we followed the patients for a year.

After 12 months, all of those who got the placebo light developed multiple sclerosis. Those who were given narrowband, only 70% developed multiple sclerosis within 12 months. So this was a huge effect. 30% reduction in the conversion from the very earliest forms of multiple sclerosis to full-blown disease, and this is what we need to work on further, we need to be able to show this clinically more definitively.

The wonderful thing is we then had a biobank of cells and blood from these participants. And we've been able to find a little bit of mechanism by which UVB might be working.

Particularly through the blood. And also, the participants loved the treatment. They loved it, they felt something was being done for them.

They can, now being shown that the light boxes can be given at home. So really, we think we are advancing in being able to use a component of sunlight to dampen autoimmune disease, like multiple sclerosis.

CHAKRABARTI: And to be clear, these light boxes are not like tanning beds, right? They're different.

HART: No. They're narrowband UVB. The dermatologists have been using them for decades, and as I said, they're now so safe. The health funds in the U.S., Kaiser Permanente is supporting them for use at home. Not in a clinic, but at home.

CHAKRABARTI: Yeah. Okay. Professor Hart and Dr. Weller. Hang on here for just a second, because by this point in the show, I know that many dermatologists, especially in the United States, are probably ready to scream at me because of their profound concerns about excessive sunlight exposure on the skin. So to that point, we did speak with Dr. Veena Vanchinathan. She's a board-certified dermatologist who practices in the San Francisco Bay Area, and she's a member of the American Academy of Dermatology.

VEENA VANCHINATHAN: My opinion as a dermatologist is that minimizing sun exposure as much as possible is ideal. Bring your sunscreen with you as much as you can, bring your hat with you, and that will go a really long way at preventing you from developing skin cancer or those signs of premature skin aging.

My opinion as a dermatologist is that minimizing sun exposure as much as possible is ideal.

Dr. Veena Vanchinathan

CHAKRABARTI: Vanchinathan says that, yes, the sun feels good and it's impossible to avoid sunshine completely, but she in her opinion, those small amounts of exposure over time really do add up.

VANCHINATHAN: So five minutes walking your dog or 10 minutes walking to your mailbox, driving without wearing sunscreen. Adding in a couple beach days. In general, for most Americans, harmful sun exposure isn't really coming from the 4th of July or that day at the beach.

It's really coming from the day-to-day cumulative effects of ignoring those five minutes.

CHAKRABARTI: Dr. Vanchinathan says exposure to UVA and UVB rays from the sun can cause fine lines, wrinkles, and brown spots on the skin. And of course, the big concern is it can also cause skin cancer.

VANCHINATHAN: Data in the United States shows that approximately one in five Americans will actually develop skin cancer at some point in their lifetime.

Most commonly, a type of skin cancer called non-melanoma skin cancer. Those encompass two large buckets called basal-cell carcinoma and squamous cell carcinoma. Those are the two most common that we're going to see that can be quite directly linked to sun exposure and our sun protection habits.

CHAKRABARTI: And for melanoma, it is true that rates of melanoma have been rising rapidly over the past 30 years in the United States. According to the American Academy of Dermatology, the AD estimates, some 212,000 new cases of melanoma will be diagnosed in 2025 alone. Vanchinathan also says the sun is strongest between 10:00 AM and 2:00 PM so it's best to limit your exposure during those hours, according to her.

You can check to make sure the UV index is below three or four before heading outside, she says.

VANCHINATHAN: It's hard to find such a clear-cut paradigm, if you will, for other cancers. Where do this, and this won't happen. And don't do that, and this cancer will develop. But we do see that with skin cancer, it's very clear that avoiding the sun and wearing sunscreen can go such a long way at preventing someone from having a really awful experience with something like melanoma or skin cancer.

CHAKRABARTI: That's Dr. Veena Vanchinathan. She's a board certified dermatologist in the San Francisco Bay Area. Okay, Dr. Weller, go ahead.

WELLER: Okay. Would love to. So basal-cell skin cancer is common of every other cancer put together. When you have a basal-cell skin cancer diagnosed your life expectancy goes up. I don't see that as a problem.

Melanoma rates have increased sixfold in the United States in the last four years. That's diagnoses deaths. Have not changed. Adewole Adamson, fantastic dermatologist in Austin, Texas. Look up his stuff, published in JAMA, in the New England Journal. So in America, your biggest risk factor. So looking at diagnoses of melanoma and how sunny it is where people live.

Great paper in JAMA Dermatology, pretty much no relationship. The biggest correlation between a diagnosis of melanoma is how rich you are. So the richer counties are, the more likely people are to be diagnosed with melanoma. The more biopsies are done, the more likely --

CHAKRABARTI: It's because they have better health care.

I'm just going to jump in here and say ...  in the United States.

WELLER: That's the argument. So look, if all of that health care was really effective, you would expect a fall in deaths from melanoma. There has been no change up or down, no significant change up or down in deaths from melanoma in the last 40 years, despite the huge rise in incidents.

CHAKRABARTI: Dr. Weller, can I jump in here?

WELLER: Yes, come in with the counter argument.

CHAKRABARTI: Yeah. Not necessarily a counter argument, but just make this a little more complex. Death is not the only negative outcome from having, from melanoma, right? So just the change in the death rate is not a good enough reason to say the increased diagnoses have not been effective.

WELLER: Look, I think not being dead is the most important endpoint. I'm agnostic about what I don't die of, whether I don't die of being struck by lightning. Don't die of skin cancer, don't die of heart disease. I really don't care.

I just don't want to be dead, and I am interested in factors, exposures that reduce my risk of death. And certainly, here in Northern Europe, the more sunlight I get, very markedly, the lower my risks of dying. So we are about to publish a paper. We had one last year, another one out here, and in the UK Biobank, this huge, great, forward-looking study of half million people in Britain.

Which has got very good data on how much sunlight exposure people got, and also education, income, smoking, exercise, et cetera, et cetera. We find that if you reduce sun exposure, for a British cohort, enough to reduce one death from skin cancer, that associates with 50 extra deaths from other causes. Now look, that may not apply directly in America, because you're a lot further south than us.

But the risk benefit ratio is enormously in favor of sunlight exposure in Northern Europe. And I suspect to a lesser degree that will apply in America. And all dermatologists think about is the skin, and that's not good medicine.

CHAKRABARTI: Professor Hart, let me turn back to you because we've only got about three-ish minutes here remaining in the conversation.

And what I'm thinking about more often, that melanoma is an important issue. I'm not going to diminish that, but we're not talking about having to go outside for 12 straight hours a day and have the sun beat down on your skin. It sounds like from this conversation that even small increases or moderate increases in sun exposure can provide some significant health benefits.

And so since you're at the Kids Research Institute in Perth, it suddenly occurred to me, I don't know if this is happening in Australia, but in the United States, there's been a growing issue over many years that kids during the school year especially, barely go outside at all.

Because the amount of recess that they're having is, has been, reduced. Are we seeing impacts on children's health from reduced sun exposure?

HART: You are so correct in that. Yes. The clearest studies are with myopia and eyes for children, but yes, with Type 1 diabetes, that's a children's disease.

In fact, we know a lot of autoimmune diseases start in childhood, may even start in utero. And yes, sun exposure is so important there, and I think Richard brought it up, it's the risk to benefit ratio. And I think dermatologists, the American dermatologists, all they think about is risks. We've really got to move that pendulum a bit more to considering the benefit.

So a little bit more sun exposure. We say never get sunburnt. Because sunburnt is the initiating event for melanoma. We just say, never get sunburnt, but certainly get sun exposure. Because that is going to be homeostatic and so good for you for health.

Never get sunburnt, but certainly get sun exposure. Because that is going to be homeostatic and so good for you for health.

Prue Hart

CHAKRABARTI: This is really key. Get more sun exposure. Don't get burned.

Okay. I have a question for you though. Depending on, maybe this is highly variable depending on each individual, but how can we measure what that threshold is between a healthy amount of sunlight, and I might be outside long enough to get burned.

HART: I would say just never get sunburnt. Everyone, you have to consider your own intelligence when you're going to get sunburnt. And I think just make sure you get out a little bit every day and get a little bit more than you might have been getting up to, you'll feel better. Your energy levels will improve. Your whole-body health will improve. But never get sunburnt.

CHAKRABARTI: It's so funny. Maybe I'm just not that sun intelligent myself, but when I'm outside for a long time I do wear some sunscreen. But when I don't reapply it, sometimes I don't realize that I'm getting close to being burned until well after the fact. Maybe that's because I've got brown skin. Who knows.

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