The Case for Sunshine (with Rowan Jacobsen)

Rowan Jacobsen: Thanks, Russ. Great to be back. I hope I get another first place this year.

Rowan Jacobsen: Hey, it worked last time.

Rowan Jacobsen: The basic idea is that we are now at a point where enough science has filled in that we need to reconsider what has been, as you say, the perceived wisdom on sun exposure. That, the recommendations we’ve received for the past few decades no longer accurately reflect what we know about the science.

Rowan Jacobsen: Yeah, for sure. And, it has actually become more strident, those recommendations, over the years. The sun is a killer. We all agree that sun exposure will raise your risk of skin cancer. And so, based on that fact, the authorities have recommended that people first reduce their level of sun exposure, and more recently pretty much eliminate any sun exposure where your skin is unprotected by either clothing or sunscreen.

And, that was part of the reason I decided it was time to write the book. When I started to see in the past few years that the typical advice you’d see in the media was stay out of the sun, summer, winter, no matter who you are, no matter what your situation is. Use sunscreen even if you are going to be indoors all day and it’s winter. And, that didn’t reflect what the researchers had been discovering for a few decades.

Rowan Jacobsen: Yeah. When you said the sun is a killer, I almost wanted to jump in and say, ‘Well, it is, but it’s also a giver of health and vitality.’ And, that part has been left out of the equation for a while.

The sun–we’ll get into this–but the sun improves–we now have pretty solid evidence that moderate sun exposure improves health in lots of both direct and indirect ways, and that was what was left out of the equation. When we’re told the sun is a killer–it raises your risk of skin cancer–that’s true, but that’s obviously a very small portion of overall health and longevity.

And so, there’s a metaphor that some of the researchers use, which is that it’s like if orthopedists started telling people, ‘Stop exercising because when you exercise, your risk of knee injury goes way up. We’re seeing a lot of knee injuries from exercise; therefore, never run. In fact, don’t even walk around if you can help it. Just sit down because that way, that’s going to take the pressure off your knees.’ And, they weren’t taking into consideration these other pieces of the picture. That’s kind of what’s happened with sunlight.

Rowan Jacobsen: An, that’s partly what drew me into it and made me want to really devote myself to a book-length work on it.

Yeah, there’s actually decades of science in multiple different fields that have been discovering these benefits of sunlight, and they really haven’t come into the public discussion. It’s just how science works: there’s a lot of specialization in science. These researchers would publish their study and they’d say, ‘Well, it looks like sun exposure might be good for you in this case,’ but it wasn’t their job to take it any farther than that. So, the papers get published and they kind of just disappear.

So, once I started seeing so many of them out there, and realized there was kind of nobody whose job it was to bring it all together and try to synthesize that into some sort of overall understanding of what was going on, it seemed like that was a pretty good way to focus my time and energy.

And, it is–you’re right to be skeptical. I was skeptical at first, too. Any time you hear something that really diverges from the recommendations of the experts in the field, you immediately wonder about quacks and where the information is coming from. And so, it’s great to be skeptical. And, one of the things I’m hoping this book does is just bring that conversation into the general discussion, rather than try to make a slam dunk case for it.

Rowan Jacobsen: Yeah. There’s a fascinating history that I wasn’t really familiar with until I dived into the book, and I think we’ve mostly forgotten about it. But, yeah, we had this amazing era of heliotherapy in both Europe and the United States; and really, peaking in the early 1900s. And, as you mentioned, it really all came out of tuberculosis to a large degree. Now, tuberculosis is still a big–if you look at mortality figures worldwide, tuberculosis is still a big player. But, back in the 1900s, it was a massive–sorry, the 19th century–it was as huge problem. I think one out of every four deaths in Europe was due to tuberculosis in the later 1800s.

A scientist from the Faroe Islands–of all places–was the first to realize that cutaneous tuberculosis–tuberculosis can go in two different directions. It can either infect the lungs–which was the classic consumption of romantic poetry–or it can be cutaneous: it can affect the skin and just eat flesh. They’re both really bad. Or, they were before antibiotics.

Anyway, this Faroe Islands doctor named Finsen discovered that concentrated sunlight could kill the cutaneous tuberculosis and could cure cutaneous tuberculosis. And that became a big deal.

At the same time, doctors were discovering that another disease that had popped up in the Industrial Revolution–rickets–was caused by lack of sunlight. All the kids in tenements in the United Kingdom and elsewhere who were never exposed to the amount of sunlight they would have back in the farming days were coming down with rickets. Which is a terrible disease. Your bones never get hard as a kid, so you get bowed legs and deformed skulls. It was also a big problem in this era. That also turned out to be cured by Vitamin D, and they discovered that it was sunlight hitting skin that produced Vitamin D.

So suddenly, two of the major diseases of that late 1800s period–rickets and tuberculosis–were being fixed by sunlight. And, there were clinics popping up everywhere to do so. And it came to be known as heliotherapy. And, people would go up to the Swiss Alps where the light was really good, to the sanitariums up there, to take the light. We know that era of the magic mountain where people would go up to Alps to the sanitariums for the fresh air. But fresh air was only part of it. The light, the quality of the light, was the other part of it.

And so, once people started thinking about light as a thing that could cure these diseases, they did go a little too far, and they began asking, ‘Well, what else might light cure?’ And, doctors kind of started noticing that people who got a lot of light and fresh air tended to be healthier than people who didn’t.

So then you could see through the 1920s, 1930s, the top medical experts of the time all really getting on board the light train and saying, like, one of the keys to public health is that everybody gets light. And, schools were redesigned to make sure that kids got more light. The kids would be sent out to play in their underwear. It was really this crazy, crazy era. There’s spectacular photos from this time. Like, in Switzerland of kids just in their boxer shorts, sitting in the snow at their desks, taking their lessons. And instructors, also in their boxer shorts, instructing the kids.

It was pretty incredible. And, everybody was on board with it. Until the 1930s and 1940s–the first inklings that all that light might also be causing skin cancer began to appear. At which point, things started to flip in the other direction.

Rowan Jacobsen: Yeah. Skin cancer, there’s three major types of skin cancer. One is squamous cell carcinoma [SCC] and one’s basal cell carcinoma [BCC], and those often get referred to as SCCs and BCCs. And those are responsible for about 98% of all skin cancer cases.

Then the third important type of skin cancer is melanoma, and that’s more like 2% of skin cancer cases. And, I’m sure we’ll dive into this later: Melanoma is the one you really want to worry about, that has–there’s significant mortality associated with it.

The SCCs and the BCCs are the ones–everybody you know tends to get after they hit age 70 or 80. You have to cut them off because they’ll keep getting bigger, but they very rarely become invasive. So, they’re not associated with significant mortality in any way.

Weirdly, none of those diseases were very prevalent before about World War II. Like, back in the day–in the early 1900s–skin cancer was something that sailors got. Sailors get a ton of sun exposure. They also get terrible diets, and your diet does affect your risk for skin cancer. So, sailors, maybe the occasional farmer, would get a skin cancer, but it was not on doctors’ radar at all.

And then, somewhere around World War II, numbers go way up. And, partly, as you’re referring to–it was partly just a demographics issue. As public health gets better and people don’t die of cardiovascular disease or infectious disease at earlier ages, they live long enough to get skin cancer. And, not just skin cancer. You see this funny, confounding trend in lots of different areas where, as public health improves, rates of cancer go up per 100,000 people because people are living long enough to get cancer. You got to die of something, right? So, cancer rates tend to go up when other things improve. But, then, you look at the age-adjusted numbers, and maybe they’re not going up as much as you thought they were.

So, yeah, what happened in the second half of the 20th century in the United States and Western Europe is that people were living longer. But skin cancer cases were exploding, like, even more so than could be accounted for by longer life.

So, that was when this sort of panic started to set in that some sort of epidemic was underway. And it had to be sunlight, because we’d, you know, shown in lab tests that if you zap a mouse with enough UV [ultra-violet], you can create skin cancers on it.

So, basically, doctors assumed that the entire rise of skin cancer was because people were being irresponsible and were exposing themselves to a ton more solar radiation than they used to back in the day. So that’s when the messaging started, and then eventually got more strident: that you needed to stay out of the sun.

Rowan Jacobsen: Okay, I’m going to lead in with a fun fact. What’s the number one best predictor of whether you will be diagnosed with skin cancer in the United States? It’s not sun exposure. I’ll give you that one for free.

Rowan Jacobsen: It’s how many dermatologists there are in your county, and the overall age bracket for people in your county. And, that is to your point about diagnosis. The more you look for something, the more you’re going to find it. And, a huge amount of the rise in skin cancer cases is because we’re looking a lot more carefully.

Now, that’s not a bad thing. Right? If you’re finding skin cancers that might maybe got missed before and never diagnosed, never even made it into the records, that’s a good thing, and that’s definitely been one thing that’s happened.

Rowan Jacobsen: Right. And that’s all to the good. And, as long as you don’t start to panic–because now that you’re looking, you’re finding a lot more–and think that something has changed that needs to be dealt with.

And yeah, as you said earlier: you look back at some of these early papers about the rise of skin cancer, and it is almost laughable how bad some of the reasoning was.

Like, the earliest–in the United States, the earliest solid data on skin cancer was, like, this Connecticut registry in the 1940s. For whatever reason, Connecticut started doing it a little bit before any other State. So, to compare rates of skin cancer today to Connecticut in the 1940s, the researchers literally assumed that back then, in the 1930s and 1940s, nobody ever exposed their skin to the sun. You can actually read these lines in the papers and go, ‘What are they talking about? Have they looked at photos of people on the beach in the 1930s and 1940s?’ But, the idea was that back then, people were much more conservative. They never spent any time in the sun. So, the entire rise in skin cancers is because now we’re spending so much more time in the sun.

Rowan Jacobsen: Right. And, I’ve actually looked for good numbers on time spent outdoors, and unfortunately, it doesn’t really exist. The best numbers you see are for kids. There’s some studies that have tracked kids’ outdoor time over the decades and you see, unsurprisingly, a gradual decline per decade from a few hours per day back in the 1940s and 1950s. When I was a kid in the 1970s and 1980s, after school we would be outdoors playing all the time. Now there’s a lot more indoor time and kids get less than an hour per day. So, we know with kids that there has been a gradual significant decline in amount of time spent outdoors.

I think we generally assume that is true for adults as well. People spend a lot more time indoors on screens than they used to. But, there isn’t any real solid data about how much time we’re getting outside.

Rowan Jacobsen: Right. And this has been looked at most closely with melanoma; and there’s been a lot of discussion in the research community about over-diagnosis with melanoma. Everyone agrees that over-diagnosis is going on, but again, maybe it’s not that much of a problem because you want to make sure you catch them all. You want to err on the side of taking off anything that might be problematic down the line.

Actually, one thing that we should mention is that until a melanoma becomes invasive, we don’t actually have any solid way of predicting whether it’s going to be a problem or not. So, all the ones that are caught very early on the skin and are called melanomas, they might be fine. But, obviously, if a doctor says to a patient, ‘It might be fine, or it might not. Do you want me to leave it?’ Like, ‘No.’ You’re going to get it cut off.

So, all these things get called melanomas and get cut off, and everyone agrees that some of them would not have been called melanomas back in the day.

And, there was actually a really interesting study a few years ago where they took slides of lesions that had been called melanomas 20 years ago. Or, lesions that might or might not be called melanomas. And, they took the exact same slides that had been done 20 years ago and showed them to a group of dermatologists 20 years later–including, actually, some of the same dermatologists who saw the slides 20 years earlier–and asked them to make the call: melanoma or not melanoma. And, 20 years ago, 11 were judged to be melanomas; and today, the exact same slides, 18 of them were judged to be melanomas. So, we’re getting more lenient on what we call melanomas.

And, like we said, that’s not necessarily a bad thing, but that is definitely a big factor in the rise of melanoma incidence. Because, when you look at mortality in melanoma, there’s been no change. Decade, after decade, after decade, mortality is totally flat, while incidence is rising steeply. And, as some scientists have pointed out, that’s the classic sign of over-diagnosis.

Rowan Jacobsen: A shirt, right.

Rowan Jacobsen: So, this is an inconvenient truth that has been lurking in the background and dogging the industry for a long time. Yeah, rates of skin cancer and rates of sunscreen use track each other spectacularly well. Decade after decade, sunscreen sales, through the roof compared to what they used to be; and yet rates of skin cancer also go up.

And, all the epidemiological studies tend to show that more sunscreen use is correlated with more skin cancer, which was also an inconvenient truth. Except you look at it and you’re like, ‘Well, that’s fine because whose using sunscreen?’ People who have paler skin who might need it more–

Rowan Jacobsen: People who are out in the sun more. That’s also–it can be a little awkward.

Rowan Jacobsen: Classic reverse causation, exactly.

But, it sure as heck hasn’t been helping as much as we might have been led to believe that it would. That’s clear. That SPF rates have gone up, adoption has gone up, people are using more, people are avoiding the sun more–it’s not turning skin cancer cases around at all. So, clearly, there’s more to the story than pure exposure to sunlight.

Rowan Jacobsen: It is, it is.

Rowan Jacobsen: Right. It’s almost like extra strength Tylenol. The bigger number seems like we’re helping ourselves more.

So, SPF: that factor is how many more times you can stay out in the sun when you’re using it without burning, until you burn, than you could if you had nothing on. So, if you could stay in the sun for 10 minutes before you start to burn with nothing and you put SPF-20 on your body, you could stay in the sun for 200 minutes [=20×10] before you got the same amount of burn going on. And then, so SPF-50, you can stay out in the sun 50 times as long before you start to burn.

Originally, the FDA [Food and Drug Administration] wasn’t even going to let the industry use anything like SPF-50 because nobody should be staying in the sun that long. But, basically, that’s a measure of what percentage of the ultraviolet light it’s blocking.

And, it’s important to understand that sun burns are caused by UVB [Ultraviolet B]. We divide the ultraviolet light spectrum into UVA [Ultraviolet A] and UVB, and they actually have very different effects on the body.

And, UVB was the first one we worried about. It was also the only one the original sunscreens were able to block. So, those first sunscreens focused purely on UVB, which turned out to be a big problem. And, SPF only applies to UVB. So, you can have a sunscreen that’s SPF-50, which means it will block UVB 50-times as well as nothing, meaning basically it’s blocking 98% of the rays. Only 2% of the UVB rays are getting through to the skin. That doesn’t mean it’s blocking UVA at all, necessarily.

And that was a problem in the old sunscreens that we all were using in the 1970s and 1980s before what they called the broad spectrum or full spectrum sunscreens came on the market later.

Rowan Jacobsen: Yes, and it looks like they did. And, the new sunscreens are way better now than those sunscreens were a generation ago.

And actually, starting next year, we’re going to get even better ones on the market, it looks like. The sunscreens that are used in Europe and Asia and Israel are much better than the ones that are allowed in the United States–and we can get into why. But, the U.S. ones are a generation behind, basically. And, yeah, they used to only block UVB because originally, we thought UVB was what caused skin cancer. UVB is what causes sun burns; and yeah, those early–they weren’t sunscreens. They were sun tanning aids. The whole point was to keep you from burning so you could stay in the sun longer, so you could get even more bronze. And then, they sort of pivoted to a health aid later on.

But they were only blocking UVB, because at the time, the doctors thought that UVA was not a problem. UVB, we knew it had enough energy in those light photons that if it hit a DNA [Deoxyribonucleic acid] molecule in your skin, it could actually mess up the DNA and give you skin cancer. So, we thought we had to block those UVBs. And, the original ingredients that were used in sunscreen–those chemical filters–were able to do that. So, it seemed serendipitous: Block the sun burn, block the UVB so you’re not going to get skin cancer; let the UVA through, and you’re going to get tan from that. Perfect.

By the 1980s and definitely by the 1990s, everyone was realizing that UVA was actually indirectly causing skin cancer as well and was probably a bigger problem than UVB all along. Which suddenly made those sunscreens look terrible–like, possibly worse than nothing–because by blocking sunburn and making you think you were safe from skin cancer, they were allowing you to stay in the sun–depending on the SPF–10, 15, 20, 30-times longer. And, all of that time, gobs of UVA was pouring into your body and probably contributing to melanoma, we now know.

Rowan Jacobsen: I think it’s actually a huge problem, and it has kind of been swept under the rug a little bit.

Now, mostly broad-spectrum sunscreens are on the market. And frankly, no sunscreen that doesn’t block UVB and UVA should even be allowed on the market, I don’t think. And, they’ve gotten much better. And you see that–in all the observational studies that track sunscreen use and skin cancer, the early ones from the 1970s show no effect, and often a reverse effect. It was worse to use the sunscreens. By the 1980s and 1990s, it’s looking like an even wash.

And now, the more modern ones, it’s starting to look better for sunscreen now.

So, I think the new ones are pretty good. I think they can be a very useful part of any sun program that you want to develop. And, they’re going to get better still in the United States; and they’ve been better for a while in most of the rest of the world.

Rowan Jacobsen: Yeah, it is starting to look a little bit like it’s, like, cheating on the test basically to take the pill. It’s not doing the thing that was the goal all along. But, it took us a while to get to that point.

Back in the 1980s, it started to look like Vitamin D was really important to health. Because, again, of all this observational data where you look at populations and the group that has low Vitamin D levels has higher rates of every disease you can think of across the board. Cancer, cardiovascular diseases, autoimmune diseases, Alzheimer’s, other types of dementia, diabetes, you name it. Low Vitamin D looked–it was associated at least, with–

Rowan Jacobsen: with all of these different things. Yeah, yeah. So, it seemed like–and then the mechanistic studies in the lab would also show that add more Vitamin D to these cells and it prevents cells from growing cancerous and improves membranes. We know originally that it helps mineralization in the bones so you get strong bones from Vitamin D, going back to the rickets days.

Anyway, it looked like there were reasons to think that it really was kind of a wonder drug that could help all these conditions. But by then, by the 1980s, we were also really worried about skin cancer, so doctors weren’t about to say, ‘Go out and expose your skin to sunlight,’ which is the natural way to make Vitamin D. So, everyone started recommending supplementation, and people did it. It’s the most prescribed supplement in the world, I believe.

And, there have been huge, really rigorous, high-powered clinical trials where half the people get Vitamin D pills and half the people get placebos, and they’re tracked for years–because it seemed like it was worth putting all that money into these trials because this really did look like a wonder drug. They have completely failed across the board where we know that unless you are extremely Vitamin D deficient, raising the amount in your blood through a pill doesn’t help with any of these conditions.

And, there’s even been the editors of the New England Journal of Medicine have published editorials saying, ‘Stop prescribing Vitamin D pills. It’s not helping.’ But, that hasn’t happened. It’s still the most prescribed supplement.

I think some doctors know that it doesn’t do much, but it doesn’t hurt. It makes their patients feel better and placebos are not nothing.

Rowan Jacobsen: Some doctors probably don’t, haven’t looked at some of the research.

But, yeah, so there’s the conundrum. People who naturally have high levels of D in their body have lower rates of all these diseases. People who artificially raise the level in their blood through a pill, it doesn’t help at all. So, how can that be?

Rowan Jacobsen: Very sunny–

Rowan Jacobsen: Yeah, exactly. Moderation, once again, is going to end up being the best policy here.

You mentioned once you’re 70, it’s harder to make Vitamin D. And yeah, that’s important. I was just looking at some numbers on this. Basically, yeah, by the time we’re 70, we’re only producing half as much Vitamin D for the same amount of sunlight as when we’re in our 30s. There’s no good: but on that, it just sucks.

Rowan Jacobsen: Right, right.

Rowan Jacobsen: Wisdom, however, way up.

Rowan Jacobsen: One of the questions with the whole Vitamin D story is whether Vitamin D was actually responsible for all those health benefits in the people that were getting more sunlight, or whether it was just along for the ride. It was an indicator of sun exposure, but it wasn’t the agent that was bringing the good health necessarily. That, it could be other things about sunlight. So, even if you’re 70, you’re not making Vitamin D like you used to, you probably are still getting some of these benefits of sunlight from other things, which we can talk about if you want.

Rowan Jacobsen: Yeah. So, the trade-off question is the right question to ask. And, the first person I ever saw ask that question was a dermatologist in Scotland named Richard Weller, who had done some research that showed that when sunlight hits skin, it produces nitric oxide in the skin. And, nitric oxide is a well-known vasodilator. It allows blood vessels to expand and lowers blood pressure because of it. It’s used in a lot of heart medications. Even Viagra is based on nitric oxide. It lets more blood flow.

His studies have shown that shining the equivalent of 20, 25 minutes of summer sunlight on volunteers–his grad students–just shining it on their arm would lower their blood pressure. It raised nitric oxide in their blood. It produced nitric oxide in the skin; that nitric oxide went into the circulatory system; and lowered blood pressure by, like, five or six points. Which would be enough worldwide to reduce deaths from heart disease by a million people or something.

So, he was the first person to ask that trade-off question. He ended up doing a TED Talk [Technology, Entertainment, Design], which you can still find out there.

Rowan Jacobsen: And, the reason he wanted to ask the trade-off question was because–skin cancer, we hear a lot about it, but it doesn’t actually kill very many people. It’s not a significant cause of mortality. In the United States, it causes–about 10,000 people a year die from skin cancer. That’s not nothing. If we could get 10,000 to go to zero, that would be great. But, cardiovascular disease is closer to a million people, and cancer is maybe 600,000 people, so those are the biggies. And diabetes is another big one; and infectious disease.

So, skin cancer worldwide, it’s not even on the charts in terms of mortality. It’s not one of the top 40 causes of death in the world.

So, if sunlight would slightly raise the risk of skin cancer but would slightly lower the risk of cardiovascular disease alone, that would be a massive win in terms of the trade-off. I didn’t get this new study in the book, but Weller and his group just came out with a new pre-print about a few months ago that looked more specifically at the trade-off question. And, to do so, they used the U.K. Biobank, which is this fantastic dataset that more and more researchers are using.

And, what happened is back in the early 2000s, there was this push to create an incredible health dataset in the United Kingdom, so they got 500,000 volunteers in the mix, took every health metric they could, questionnaires. Got every possible granular detail about these people’s health, and they were all ages 40 to 69, so they were all middle age. And then, they’ve been tracking that group of 500,000 people ever since, so we now have about 20 years of data on them. And, it’s such a rich source of data that even though observational data can be an intellectual cesspool, this is a pretty good one. So, you could get away from some of the problems if you’re using small datasets.

So, Weller took a look at that group; and you have location data for all of them, and some of them have even had their sun exposure tracked. But, even if you haven’t attached a light-sensing wristwatch to the volunteers, you can check the satellite data for their location and get a pretty good sense of how much light they’ve been exposed to on average.

So, he just published a pre-print that tracked this group–I think they had 420,000 people ultimately in their study–mortality and incidence of disease against sun exposure. And, they didn’t just do sun exposure, they also asked the people about sun habits. Did they seek sun? Did they actively try to get some sunlight? So, they scored everyone for a sun-seeking habit and tracked that against disease.

And, what they found was that in all of the 420,000 people, about 45,000 had died. Period. Almost all cardiovascular disease and cancer were responsible for most of those diseases. Only 440 had died of melanoma; only 60 had died of other skin cancers out of 420,000 people. So, skin cancer doesn’t kill very many people.

And what they found was that, yes, the people who got a lot of sun versus a little sun were about 20% more likely to die of melanoma. The people who got a whole lot of sun were actually no more likely to die of melanoma. So, there was a slight rise in melanoma deaths for the high-sun people, but that amounted to less than 100 people overall over 20 years in this set of 420,000 people. Meanwhile, they were far less likely to die from cardiovascular disease or cancer, and some other diseases that contributed minor numbers. So, I think the ratio was 75:1, that more light, for every one extra death from melanoma that it created, was saving about 75 deaths from other bigger, more problematic diseases.

Rowan Jacobsen: Yeah, I’m so glad you brought that up. Because learning more about the science behind this and becoming more comfortable with the sun, it improves your life on a daily basis. You realize that you had that fear in the back of your mind that was probably unnecessary. And so, just like with anything else when you thought you had to fear something and you suddenly realize that maybe your fears were a little overblown–like, that improves your life.

And, the evolutionary part of this, I think, is actually really important, because as you correctly point out, a lot of the information we have about what looked like to be these benefits of sunlight are coming from observational studies. And, yes, the scientists do try to control for all the usual confounders, but that is a dark art.

Rowan Jacobsen: So, all we can do is go, ‘Well, that’s interesting.’ And, we’re not going to get great randomized clinical trials where half the people expose themselves to a lot of sunshine and half don’t, because it would be unethical since we think they might be raising their risk of skin cancer. No funding agency is ever going to approve those studies.

So, it’s food for thought; but what’s interesting here is we also–the reasons that we believe that skin cancer, that sunlight causes skin cancer, are also from observational studies. We’re not doing long-term clinical trials where we tell half the people to go out and fry themselves and we see if they get skin cancer. So, it’s all kind of guesswork, and any time you’re in that kind of situation, you kind of then want to default to evolutionary norms and ask: Well, what do we have a pretty good track record of doing and what’s the weird intervention that’s new?

And so, in this case, human beings spent their first hundreds of thousands of years getting 12 hours of sunlight a day. No other species that’s out there seems to be suffering from too much sunlight. It seems to be just us that are having this issue. So, what changed? Well, we switched to indoor life, mostly in the past 100 years. And, that’s the weird thing that we need to start being skeptical about. Did something happen in that switch to indoor life that messed things up?

Rowan Jacobsen: Yeah, and I would totally agree. Take it all with a grain of salt. I’m certainly not a doctor either, and people shouldn’t be forming their medical opinions just from my book. But I do hope people start looking into it because of my book.

And, we’re now in this kind of amazing era where we have these incredibly powerful research assistants on-hand all the time–the LLMs [large language models]–that have read everything. And, it is pretty amazing: If you ask them, ‘Show me the studies on X or Y,’ they’ll pull them up. And, you don’t want to trust the AI [artificial intelligence] because it can get the conclusions wrong sometimes, but it will point you toward the sources, and then go to the direct sources. They can’t be hidden; it finds them all. So, it’s actually better than it’s ever been to look around and find what the foundational research is on these topics. So, that’s really worth doing.

But, in terms of what I think can be actionable advice for people, it’s: Err on the side of moderation all the way, but don’t get zero sun exposure. It’s very clear, no matter how we look at it, that zero sun exposure is not healthy for people. It’s also clear, and every scientist I’ve spoken with agrees, that burning is bad. If you’re actually getting a sunburn, it means you have fried those cells beyond the point that they can recover, so they’re basically all just committing suicide and taking themselves out of the game so they won’t turn into cancer. But they don’t even do that always successfully. So, burns are truly a sign that you’ve gone too far.

And, I know from my personal experience that even when I’m trying not to burn, it can sneak up on you. So, my own rule is to err well on the safe side of burning–to never get close to a burn. That said, I don’t sweat the small stuff. I’m going back to what doctors told us to do in the 1950s and 1960s. Don’t get sunburn at the beach, don’t get overexposed. But a little incidental sun exposure during your day is probably a very healthy thing.

That’s really going to be influenced by who you are, where you are, and especially your skin tone. People with darker skin tones can take a whole lot more sun exposure than people with light skin tones. And, people with the lightest skin tones, who often have red hair and reddish freckles, are the ones who are super-susceptible to melanoma. So, they are the ones who do truly need to really be careful. The recommendations are kind of written for them, with the assumption that everybody else can just do the same thing and they won’t be harmed by that. But, now we’re realizing that people with darker skin tones really shouldn’t be doing the same thing as the people with very fair skin.

Rowan Jacobsen: Thanks, Russ. It was a pleasure.