[pmoriarty]

For those who, like me, started to wonder how using sunscreen affects vitamin D production, here's the conclusion of "The effect of sunscreen on vitamin D: a review":

"There is little evidence that sunscreen decreases 25(OH)D concentration when used in real-life settings, suggesting that concerns about vitamin D should not negate skin cancer prevention advice. However, there have been no trials of the high-SPF sunscreens that are now widely recommended. What's already known about this topic? Previous experimental studies suggest that sunscreen can block vitamin D production in the skin but use artificially generated ultraviolet radiation with a spectral output unlike that seen in terrestrial sunlight. Nonsystematic reviews of observational studies suggest that use in real life does not cause vitamin D deficiency. What does this study add? This study systematically reviewed all experimental studies, field trials and observational studies for the first time. While the experimental studies support the theoretical risk that sunscreen use may affect vitamin D, the weight of evidence from field trials and observational studies suggests that the risk is low. We highlight the lack of adequate evidence regarding use of the very high sun protection factor sunscreens that are now recommended and widely used."

https://pubmed.ncbi.nlm.nih.gov/30945275/

[49531]

Fortunately Vitamin D supplements are a safe and effective way to get the recommended amount. UV exposure is the most preventable cause of skin cancer[1] and not worth the risk.

EDIT Forgot my link: 1. https://www.hhs.gov/sites/default/files/call-to-action-preve...

[gojomo]

But, after 50+ years of rising sunscreen use, there's essentially no data showing more sunscreen use reduces skin cancer.

Sunscreen definitely prevents sunburns, and almost certainly delays visible skin aging/weathering. Those may be enough benefits for some people.

But the people/populations using more sunscreen are also having more skin cancer. Some theories compatible with these observations are:

• While preventing sunburn pain, sunscreen doesn't prevent the actual cancer-causing skin damage - and thus by allowing more time to be spent in the sun, actually worsened skin cancer rates. (This may have especially been a problem for the 1960s-1990s, when it was thought that only sunburn-causing UVB contributed to skin cancer - so sunscreens only blocked UBV. That encouraged increased exposure to the mostly-unblocked UVA, now understood as an equal contributor to skin cancer. More recent sunscreens block UVA as well.)

• Known carcinogens commonly used in sunscreens, or present as contaminants, are actually causing increased rates of skin cancer.

Anyone whose true worry is skin cancer should use shade & limited times of exposure - not sunscreens. (Ensuring a spaced-repetition of gradually-increasing exposure, to develop a natural tan without ever reaching a peeling burn, is also likely naturally protective against skin cancer.)

Further, while endogenous Vitamin D production relies on sun exposure, and low Vitamin D is correlated with health problems, oral Vitamin D supplementation may not replace all the benefits of sun exposure.

Generally, large population studies show positive effects of moderate sun exposure on many health outcomes, including overall longevity, heart disease, and non-skin cancers. Meanwhile, Vitamin D supplementation studies have usually not found that such supplementation alone reverses the correlations of many diseases with low Vitamin D. Thus, Vitamin D may not be the only mechanism by which sun's benefits are achieved.

So rigorous sun-exposure-minimization, even if it does reduce (often benign or increasingly survivable) skin cancers, may increase overall mortality through higher heart disease & other cancers. (Your HHS report mentions 9,000 skin melanoma deaths per year. There are 650,000 heart-disease deaths and 600,000 other cancer deaths.)

Get sun. Use shade, clothing, & timing to ensure it's not so much sun that you peel. Use sunscreen sparingly, only when you can't moderate sun exposure other ways.

[wahern]

> But, after 50+ years of rising sunscreen use, there's essentially no data showing more sunscreen use reduces skin cancer.

50% reduction in melanoma: https://pubmed.ncbi.nlm.nih.gov/21135266/

40% reduction in squamous cell carcinoma: https://pubmed.ncbi.nlm.nih.gov/10475183/

See, generally, https://www.skincancer.org/skin-cancer-information/skin-canc...

Perhaps you were thinking of basal cell carcinoma, the most common type of skin cancer. There does seem to be a lack of experimental evidence wrt BCC: https://www.hindawi.com/journals/jsc/2012/480985/ The skincancer.org FAQ conspicuously skips around that hole.

[gojomo]

Melanomas are the skin cancer of primary concern.

Your "50% reduction in melanoma" link is interesting, but pretty small & low-powered - and followup comments (such as https://ascopubs.org/doi/10.1200/JCO.2011.35.5727) highlight potential major problems in study design. For example:

• Study wasn't originally designed to detect effect on melanomas - that endpoint was added later. (This, alone, suggests possible p-hacking.)

• Instructions thus didn't even direct sunscreen application to the areas melanomas most often occur. Yet, at followup both control & intervention groups had a disproportionate number of melanomas in exactly the areas where application had been directed (and most applied, by self-reports, in both groups). As the commenters note, this is actually consistent with the theory that sunscreen encourages overexposure moreso than it protects.

• Small changes in arbitrary study choices - like to what extent back/leg melanomas were considered (when those areas weren't part of the encouraged sunscreen-application area), or whether a 1, 2, or 4 year exclusion of early events applied – remove the claim of 'significance', suggesting a very fragile result.

If the protective relationship of sunscreen were real, it'd have lots of studies with robust results. Or, the massive increases in recent decades in SPF factors, sunscreen purchasing/use, and sun-avoidance messaging and practice would've reduced melanoma rates. Instead, melanoma rates keep going up. To me, that's far more powerful evidence than a repurposed study with 11 more melanomas (but fewer invasive ones!) in a slightly-less-sunscreen-using control group.

The squamous study is also murky, though not as much. Its abstract notes, "There were no significant differences in the incidence of first new skin cancers between groups randomly assigned daily sunscreen and no daily sunscreen (basal-cell carcinoma 2588 vs 2509 per 100,000; rate ratio 1.03 [95% CI 0.73-1.46]; squamous-cell carcinoma 876 vs 996 per 100,000; rate ratio 0.88 [0.50-1.56])." The same number of people got new skin cancers in both groups! It's only the secondary count of tumours where the control group had more. I'm unsure that's an important protective effect.

But going back, I really should have said: "no data showing more sunscreen reduces deadly skin cancers". There's a reasonable amount of evidence sunscreen reduces various kinds of mild skin-tumours, much like the obvious-to-the-naked-eye effectiveness against sunburns.

But for melanomas/death-by-skin-cancer – the top worry of most sunscreen users – any effect is either very weak, non-existent, or possibly even inverse.

[49531]

> • Known carcinogens commonly used in sunscreens, or present as contaminants, are actually causing increased rates of skin cancer.

I am curious to see a citation for this claim.

> Generally, large population studies show positive effects of moderate sun exposure on many health outcomes, including overall longevity, heart disease, and non-skin cancers. Meanwhile, Vitamin D supplementation studies have usually not found that such supplementation alone reverses the correlations of many diseases with low Vitamin D. Thus, Vitamin D may not be the only mechanism by which sun's benefits are achieved.

I am also curious to see these studies, and wonder if they control for other variables like physical activity.

I think it's an incorrect framework to say that you have to choose between skin cancer and heart disease, you can avoid both through different lifestyle choices.

[baumandm]

Here's a recent HN discussion of a study that found benzene in 27% of tested sunscreen samples: https://news.ycombinator.com/item?id=27292387

[gojomo]

Many intentional functional ingredients in sunscreens are known carcinogens and absorbed at levels beyond any safety testing:

https://www.webmd.com/skin-problems-and-treatments/news/2020...

Contamination of sunscreens with common dangerous byproducts of industrial processes like benzene is common:

https://www.washingtonpost.com/lifestyle/wellness/benzene-su...

By comparison, shade contains no carcinogens.

Sun exposure correlated with longer life (even while also being correlated with more cancer deaths!):

https://www.health.harvard.edu/blog/heres-something-unexpect...

An earlier broad survey also finding natural sun exposure decreasing all-cause mortality (but not use of tanning beds, despite similar effects on Vitamin D production, again suggesting D-supplements alone don't replicate the sun):

https://cebp.aacrjournals.org/content/20/4/582

I'd agree, it is hard to disentangle these correlations with things like general levels of outdoor activity and socializing.

But even so: if people who are healthy for other reasons tend to spend more time outside in sun, maybe it'd be a good idea to join them, & perhaps absorb their other habits as well, rather than live in fear of the sun? (Maybe even the sun is damaging on many levels, but the other benefits of activities inherently done more under the sun offset those effects, even if just via mood/optimism?)

I'd say instead that it's an incorrect framework to embrace an illusion of total control "through different lifestyle choices" without tradeoffs. Every activity has a mix of risks and benefits. Certain vigorous activities with a higher risk of accidental death may deliver other fitness and social benefits. If an extra 5 hours of sun every week doubles melanoma death risk, but reduces cardio/cancer death risk just 1%, that sun would still be a net-mortality benefit.

Such tradeoffs are real & everywhere. Trying to engineer both benefits – "can I do everything other healthy people do usually do outdoors indoors? can I find the least-dangerous sunscreen? will vitamin D supplments, perhaps with a bunch of other diet changes, simulate the sun's benefits?" – also includes costs, in research time, psychological focus, neurotic behaviors, etc, for diminishing returns.

[psychometry]

>But the people/populations using more sunscreen are also having more skin cancer

Um, you missed the most obvious explanation (assuming that's even true): People who have an elevated risk of skin cancer (due to geographic location and/or skin type) are likely to use more sunscreen for that very reason, but despite their sunscreen use they're still at an elevated risk of cancer because sunscreen cannot eliminate all risk.

It's really no different than saying that people who are receiving more IV chemotherapy are also dying of cancer more often than people who aren't.

[gojomo]

This sort of confounder is common, but we have in the US a population that, over the decades, is (pre-exposure) no more pale/susceptible-to-burns.

The public has been bombarded for decades with the health message to avoid the sun, and a deep tan has become less fashionable. (My younger friends, especially, treat minimizing tans/exposure as an almost religious obligation.)

Sunscreens have broadened the wavelengths they block – they used to mostly skip UVA, thinking it harmless – and upped their SPF factors. (In the 1980s, I recall SPF15 as the max - now it's SPF30, SPF80, SPF100.) Sales & usage of sunscreen keep growing.

But melanoma case rates are still on a long-term rising trend. Deaths have finally improved slightly in the last few years - likely from earlier detection & better treatment.

If the population's generally the same, but slathering on far more sunscreen every decade – but cases still go up & mortality barely budges – there's little hint of effective protection.

[lotsofpulp]

> If the population's generally the same, but slathering on far more sunscreen every decade – but cases still go up & mortality barely budges – there's little hint of effective protection.

It is not so simple to come to this conclusion. You would have to establish that time spent in sun per person has not gone up, that per person use of sunscreen (good quality sunscreen) has gone up by a measurable amount, that it is being used properly, and the cancer is happening on areas where sunscreen was used. In addition, you would have to control for people living longer.

Note that the US population in less sunny and cold areas (Midwest and Northeast) has stalled for 3 decades compared to explosive growth in population in the South and West (sunny, warm areas).

[gojomo]

The shifting of population regionally, and the aging of the population, are both good points to consider for proper controls. (In Australia, a fair-skinned population in high-UV latitudes suffers melanoma rates 50% or higher than the US. Accordingly, the promotion of sun-avoidance & sunscreen is even more intense than the US. Their age-adjusted malanoma rate reporting shows the same increase, from the 1980s through 2016: https://www.canceraustralia.gov.au/affected-cancer/cancer-ty...).

But as a longtime observer of trends, I'm pretty confident: people of all ages are conspicuously, consciously avoiding the sun more than in the 60s-80s. Indoor time has risen. Our palest most-sun-sensitive subgroups haven't increased as a proportion of the population - they've shrunk, compared to darker-skinned populations with lower base rates of melanoma.

If contra my impressions, sun exposure time has gone up, that could be due to overconfidence in sunscreens, one of the effects I'm concerned about.

If sunscreens provided the protection claimed, & this drumbeat of "slather it on always!" was an effective message, shouldn't there have been some dent in melanoma rates over the decades?

Lung cancer deaths have gone down with smoking warnings & reduced sales.

Motor vehicle deaths per mile traveled have gone down with new rules & education.

Melanoma rates seem to go up no matter how much more sunscreen is touted, is sold/used, or is strengthened in SPF or formats/staying-power.

[nomel]

The majority of my family has had skin cancer (we don't tan, we burn). It's usually in places you can't put sunscreen, like eyelids, close to the lips, etc.

[seattle_spring]

Can you provide some peer reviewed sources for your claims? Your whole comment reads like that thoroughly debunked "scientists blow the lid off of sunscreen" [1] article that was going around a few years back.

[1] https://millerfamilydermatology.com/sunscreen-myth/

[gojomo]

Here's a good recent overview of reasons to doubt the efficacy of sunscreen against fatal skin cancers:

https://www.outsideonline.com/2380751/sunscreen-sun-exposure...

(Most recently discussed on HN at https://news.ycombinator.com/item?id=23086211)

Similar doubts have existed for decades – here's a 1993 variant reporting some of the trends that already didn't add up, back then: https://www.motherjones.com/politics/1993/05/melanoma-sunscr...

Another branch reply provides more sources about sunscreen chemicals & sun-longevity correlations: https://news.ycombinator.com/item?id=27520144

[Spooky23]

I don't know why your comment is being voted down, it's a reasonable one, although I disagree with parts of it.

Depending on your skin type, "Get Sun" may not be good advice, especially if you make a mistake. A single significant sunburn in your teens significantly increases your lifetime risk of getting a skin cancer, of which melanoma is just one. My wife developed melanoma and is in remission. She is fair skinned and very sun-cautious -- typically using clothing as a primary barrier with sunscreen. Like anything risk assessment and risk tolerance is key and difficult to assess.

Another factor to consider is that mortality doesn't always tell the story. Some surgical procedures introduce significant scarring. Treatment for a stage-2 melanoma will often include removing lymph nodes, which introduce other complications. Also be careful, as past diagnoses of cancers were not great. That melanoma that moved into an organ may not have been classified correctly in 1960.

Personally, my advice is go outside, dress appropriately and use a mineral-based sunscreen if you're going to be out for more than a half hour or so. Don't go swimming at solar noon. Don't tan. Wear a rash-guard at the beach. Wear a hat at the ballgame.

[cactus2093]

There is evidence that bad (peeling) sunburns as a child are a major risk factor in melanoma. That is never going to be feasible to study in a randomized control trial, in addition to the study taking 40 years to complete it would be unethical to burn children that badly on purpose. Randomized control trials on seatbelts saving lives are also hard to find for the same reason but that doesn’t mean they don’t work.

Also, as anyone who burns easily will be well aware, sunscreen is almost impossible to use properly in the real world. You need to cover every inch of your skin and reapply every 60-90 minutes and make sure not to let it wash off by going in the water too soon or sweating too much, make sure not to rub it off with clothing or towels, etc.

The first part of your advice makes sense in light of this - shade and clothing are much more practical ways to stay safe if you’re outdoors all day and burn easily.

“Use sunscreen sparingly” is just stupid advice to be giving though. There is much more evidence to it helping than doing any harm.

[treeman79]

Long term sun exposure vs shade. Curious if sunscreen would have helped https://www.huffingtonpost.ca/2012/06/06/bill-mcelligott-sun...

[loudtieblahblah]

Sunshine is more than just a source of VitD.

UVA has also been shown to lower blood pressure. This is probably the result of UVA causing the release of nitric oxide from skin stores, which promotes widening of blood vessels. It also acts as an antioxidant to prevent damage to cells.

People who don’t get enough sunlight have altered cellular defense mechanisms that predispose them to excessive inflammation, which can result in autoimmune diseases.

One could argue you can supplement to replace VitD, but are you supplementing your children? From what age? How regularly? What's the quality of the supplementation? How do the poor maintain access to supplementation?

Then you run into the problem that long term, large(r) doses of Vitamin D causes kidney problems.

A study ( https://pubmed.ncbi.nlm.nih.gov/21430082/) found an association between low vitamin D levels and the development of type 2 diabetes. For every ten-unit decrease in blood vitamin D levels, we found a 10% increased risk of developing this form of diabetes over the following five years. when they gave supplements of vitamin D to patients with low vitamin D levels who were already at risk of developing diabetes, there was no overall improvement in their sensitivity to insulin. Nor was there a change in their blood glucose levels compared with those given inactive tablets.

I'm betting, not just in this case, but the act of your body making it's own VitaminD creates benefits we are not yet aware - that oral consumption of a pill isn't going to compensate for.

nevermind MOST of VitaminD pills use soybean oil or some other horrible Omega-6 ridden, cheap seed oil as it's delivery method.

Outside time in the sun is helpful in ways not tied to VitD, as well. circadian rhythms are regulated by bright light exposure. You can't get these lumens by waking up and sitting inside all day. The heat from the sun is capable of reducing physical stresses on the body’s cells and by increasing heat production.

Another important potential effect of sunlight is UV-induced suppression of the body’s immune system. Solar radiation does this by altering the activity of the white cells involved in turning on the body’s defence mechanisms. This may seem like a negative, but it's vital for people to reduce inflammation and when considering how the earth's population spreads out autoimmune disorders (higher percentages the more you get away from the equator), this may be a secondary factor on top of VitaminD.

IMHO -

people need to find a balance with sunscreen and sunshine. if you know you're going to risk a burn, put it on and reapply when necessary.

if you're worried about cancer, eat some cruciferous vegetables regularly to make sure you get lots of sulforaphane which protects against skin cancer. Get regular derma checkups.

but when looking at auto-immune issues (that once you have one, your supplementation isn't going to undo it), the depression issues, and so forth - isn't worth skipping out on sunshine.

Skin cancer may be the most preventable but it's also a fairly unlikely cancer, as far as cancers go - and while it's one of the scarier cancers, catching it early with derma appointments is key to survival. Catching it early has a high survival rate.

An auto-immune issue, on the other hand, will shorten your life and make you suffer along the way, increasingly, for the rest of your life. It's not just a death sentence. It's a slow-slog through hell on the way there. Most people never go into a permanent remission of Ankylosing spondylitis or MS. It just slowly destroys you, it handicaps you, and then it kills you. And along with all that suffering, is your kids, parents and partners suffering right along with you. Yay - therapy sessions for everyone.

It's not just auto-immune issues. Depression, anxiety, even certain cancers themselves all have some relation to low vitamin d.

IMHO - sunlight needs to have it's saturated-fat moment where we realize that a lot of the fear mongering simply wasn't warranted. And that the cures for some diseases end up being the catalyst for many others that are far more likely.

How many people are afflicted with an autoimmune issue? how many with debilitating depression? Compare those numbers to skin cancer. Compare the deaths. Compare the suffering.

Then try to find a balance.

[gojomo]

"I'm betting, not just in this case, but the act of your body making it's own VitaminD creates benefits we are not yet aware - that oral consumption of a pill isn't going to compensate for."

We are already aware of a direct benefit: the skin's production of Vitamin D uses up bodily cholesterol. External supplementation doesn't do that.

(I agree there are likely others we'll document later.)

[mywittyname]

Very good information.

[Toine]

That was really enjoyable to read, thanks for sharing.

[nradov]

Your risk analysis is not scientifically valid. There is no reliable evidence that moderate sunlight exposure increases all-cause mortality.

[loudtieblahblah]

it should also be noted that consumption of certain antioxidants protect against skin cancer (most notably sulforaphane found in Cruciferous Vegetables).

>Nonsystematic reviews of observational studies suggest that use in real life does not cause vitamin D deficiency.

yeah, but that's an observational study.

I'm not anti-sunscreen and if you burn or get dark/deep freckles easily, I'm even more "pro" sunscreen for you.

But when looked at the number of diseases and problems correlated to Vitamin D deficiency and looking at the relatively low risk of contracting melanoma (as scary as that cancer can be if caught late), to me it's a balancing act.

Consuming mass amounts of VitaminD over long periods of time, orally, can cause kidney problems.

If you look at auto-immune issues globally, the percentage of the populations that have them sky rocket the further you get away from the equator. Depression, anxiety, even certain cancers themselves all have some relation to low vitamin d.

Sunlight, the type that allows UV-B to penetrate your skin, is a human necessity.

And like a lot of things we need (Vitamin C and E, or polyunsaturated fats, carbohydrates, etc), too much of it will cause you problems and/or kill you, not enough of it will cause you problems and/or kill you. And trying to anecdotally perform some balancing act without constantly running tests on yourself, is difficult.

My rule of thumb is put on sunscreen if you are out long enough to risk a burn, re-apply when necessary. Otherwise, soak up the rays.

[pmoriarty]

"Consuming mass amounts of VitaminD over long periods of time, orally, can cause kidney problems."

What counts as massive?

And is consuming massive amounts of Vitamin D necessary to prevent deficiency?

[loudtieblahblah]

if you're like most of the western world, especially if you have an indoor job and indoor hobbies (we spend an awful lot of time binging tv shows, playing video games, working on computers, etc..), you're not outside all that much unless it's to hop in the car and go to another indoor place.

and chances are you have a deficiency.

Most vitamins tell you to take 2,000 IU. Upper limits are typically stated to be 4,000 IU. But there's been no established harmful upper limit either.

This leads a lot of people into thinking more is better, this is doubly true if they have some kind of pre-existing condition that's linked to low VitaminD and they're desperate to heal themselves. They read quack stories on the internet about how 10,000 IU doses help cure MS and they do it too.

It's also made worse by so-called "smart" and "qualified" people like Dr Rhonda Patrick essentially turning herself into some pop-health guru and when she tells people what she supplements with (5,000-6,000 IU), many people feel she knows what she's talking about and copies her. But the reality is, she takes A LOT of supplements and she has zero idea how they all mix with each other, especially at the supplementation levels in which she's consuming them.

of vitamins that can be abused, VitaminD is mostly safe. But a lot of folks go a bit crazy with it and have hurt themselves.

VitD supplements are also, often, in soybean oil, which is horrible for you. VitD needs to be consumed with a fat, so If you're going to supplement, you spend the extra money for it suspended in coconut oil instead.