Avoiding the sun may be as risky as smoking?

The study is called the Melanoma in Southern Sweden cohort.

Researchers tracked 29,518 women for two decades, logging their sun habits and, eventually, their causes of death. (Lindqvist et al., Journal of Internal Medicine, 2014 and 2016.)

The women who actively sought sun had roughly half the mortality rate of the women who avoided it.

The advantage came mostly from lower rates of cardiovascular disease. And the authors put it in plain terms:

A non-smoker who avoided the sun had a life expectancy similar to a smoker who got the most sun.

There's a real biological mechanism behind this.

When UV light hits your skin, it triggers the release of nitric oxide from stores already present in your skin.

This compound dilates blood vessels and lowers blood pressure. (2016 review, PMID 26766556.) That's a direct cardiovascular benefit, independent of vitamin D.

Now for the honest caveats:

This was an observational study, not a controlled trial.

It followed fair-skinned women in Sweden (a high-latitude, low-sunlight country) so it doesn't transfer cleanly to my skin in Costa Rica or yours in Arizona.

Other researchers have argued the effect could be partly explained by sicker people staying indoors to begin with.

So this is not proof that sunlight is a fountain of youth.

But it's a large, long-term, serious signal that the thing we’re supposed to fear without qualification has a cost on the other side of the ledger…

And we have the receipts.

Vitamin D deficiency is now one of the most common nutrient insufficiencies in the developed world.

This isn’t actually a vitamin, but a hormone your skin manufactures from sunlight, and it touches everything from immune function to mood to bone health. We spent four decades optimizing against one cancer. We may have ignored the bill coming due elsewhere.

If sunlight were the simple cause of skin cancer, then the people who work outdoors (farmers, fishermen, construction workers, lifeguards) should be the highest-melanoma-risk group on earth.

They're not.

A 2016 study compared outdoor workers to indoor workers.

The outdoor group had higher rates of the less-dangerous, more cumulative UV-driven skin lesions (actinic keratoses, basal cell carcinoma, squamous cell carcinoma). That tracks with what you'd expect.

But for melanoma, the skin cancer that actually kills, the study found no significant association with outdoor work. (PMID 26995016.)

A 2004 review went further.

Examining the existing data, the authors wrote that "paradoxically, outdoor workers have a decreased risk of melanoma compared with indoor workers, suggesting that chronic sunlight exposure can have a protective effect." (PMID 15005091.)

The people who get the most sun aren't the people getting the deadliest skin cancer. Office workers, who barely see the sun, get melanoma at higher rates than those who spend their lives in it.

If chronic outdoor sun isn't the driver of melanoma, two other patterns are.

The first is well-established:

Intermittent intense exposure. Which means sunburns. Especially blistering ones, and especially in childhood.

The burn is the enemy, NOT the sun.

The second pattern is barely discussed outside a specific corner of the literature:

Dietary fat composition.

Specifically, polyunsaturated fats (PUFAs) from industrial seed oils.

In 1987, researchers analyzed the subcutaneous fat tissue of 100 melanoma patients. The percentage of linoleic acid (the dominant PUFA in modern seed oils) in their fat stores was substantially higher than in controls, as was their total PUFA content.

The researchers concluded that "increased consumption of dietary polyunsaturates may have a contributory effect in the etiology of melanoma." (PMID 3110746.)

A 2018 epidemiological study confirmed the pattern:

PUFA intake was associated with skin cancer risk. No other type of fat showed that association. (PMID 29636341.)

The most striking evidence is interventional.

In 2012, researchers tested how different fats affect UV-stressed skin. Topical cholesterol (the same molecule that makes up healthy cell membranes) protected skin from UV-induced damage. Topical linoleic acid did the opposite. It aggravated the damage. (PMID 22209282.)

The epidemiology is observational. It doesn’t prove causation. The interventional study is on barrier-disrupted skin rather than melanoma directly.

But it's all converging evidence pointing at a variable the public health story left out:

Your skin's lipid composition reflects what you eat. If your diet is heavy in PUFA, your skin is too. Those fats are highly prone to oxidation when UV light hits them. The damage we've been blaming entirely on sunlight may be partly damage from oxidizing seed oils inside your own tissue, triggered by light.

That changes the protocol. The defense against skin damage isn't only what you put on top of your skin. It's also what you put into it.

But what you put on your skin does matter, and consider what kind of stuff most people use…

Because while we were told to avoid the sun, we were handed the replacement: Chemical sunscreen, every day, for life.

A 2018 systematic review and meta-analysis in the European Journal of Dermatology looked at the evidence behind that claim.

Its conclusion:

The data "does not confirm the expected protective benefits of sunscreen against skin cancer in the general population." (PMID 29620003.)

So the claim isn't that sunscreen is harmful.

Rather, its expected protective benefit against skin cancer isn't confirmed by this meta-analysis. That’s it.

However…

In a 2020 randomized clinical trial, the FDA confirmed that the common chemical filters (oxybenzone, avobenzone, octinoxate, octocrylene, homosalate, octisalate) pass through the skin into the bloodstream at concentrations exceeding the agency's own threshold for further safety testing. (PMID 31961417.)

4 comments

Avoiding the sun may be as risky as smoking?