The Link Between Sunlight Exposure and Lifespan
This Week’s Research Highlight
The Sun Exposure Paradox
The relationship between sunlight and human health is surprisingly complex.
We have long known that excessive exposure to ultraviolet light increases risk of melanoma. This, of course, has led dermatologists and other experts to discourage people from venturing into the sun unprotected.
However, melanoma deaths represent a very small percentage of total cancer deaths. For instance, in 2023, there were around 186,000 new cases of melanoma diagnosed in the United States, and less than 8,000 deaths in the same year.
Meanwhile, prior longitudinal studies in northern Europe, where sunshine can be hard to come by, have suggested that greater sun exposure is linked to reduced all-cause mortality.
In one such study, around 30,000 Swedish women were followed for 25 years, during which time they were asked about their sun exposure habits.
At the end of the study, they found, unsurprisingly, that women who reported more sun exposure had a higher incidence of melanoma. But despite this difference in cancer incidence, self-described avoiders of sun exposure had a roughly 2-fold higher mortality rate over the course of the study, compared to the group who got more sunshine.
So is it possible that by shunning sunlight, we are preventing one potential cause of death, but at the cost of increasing our risk of dying from other causes? How do we account for this possible tradeoff?
A new, much larger observational study, using more sophisticated methods to assess sun exposure patterns, might get us a little closer to answering this elusive question.
Analyzing Sunlight and Survival
Researchers analyzed data on sun exposure and mortality from the UK Biobank, a massive cohort study involving around 360,000 white participants of European ancestry.
They captured UV exposure through two distinct measures:
- Self-reported sunlamp or solarium (tanning bed) use
- Annual average residential shortwave radiation based on participants' locations
Then, to validate these measures, the researchers compared them against participants' vitamin D levels — an objective biomarker for UV exposure.
They also adjusted for various potential confounding factors, including socioeconomic status, physical activity, and risk-taking behaviors.
Findings
After following subjects for an average of 12.7 years, it was determined that higher sun exposure, by both measures, was associated with lower all-cause mortality.
People who reported using solariums showed:
- 15% lower risk of all-cause mortality
- 23% lower risk of cardiovascular disease mortality
- 14% lower risk of cancer mortality
- 12% lower risk of non-cardiovascular/non-cancer mortality
Similarly, individuals living in areas with higher natural UV exposure (equivalent to the difference in latitude between Chicago and St. Louis) experienced:
- 12% lower risk of all-cause mortality
- 19% lower risk of cardiovascular disease mortality
- 12% lower risk of cancer mortality
Beyond Vitamin D
Vitamin D has traditionally been considered the primary mediator of health benefits associated with sun exposure. However, this study points to other important biological mechanisms.
You see, ultraviolet light is made up of different wavelengths, which interact with the skin in distinct ways.
UVB primarily interacts with the epidermis, the outermost layer of skin, where it triggers vitamin D production (and potentially mutations leading to cancer).
UVA, meanwhile, penetrates more deeply into the dermis, where there is a rich reservoir of nitrogen oxides. UVA radiation can activate the release of nitric oxide into the bloodstream, which has an array of downstream effects. For one thing, nitric oxide is a natural vasodilator — it relaxes the walls of blood vessels, improving blood flow and lowering blood pressure.
This pathway is particularly notable in light of the fact that the participants in this study who got more sun exposure saw the greatest reduction in cardiovascular mortality (–19-23%), compared to other causes. Additionally, in the aforementioned Swedish study, it was determined that the shorter life expectancy of women who avoided the sun was mainly driven by a dose-dependent increased risk of cardiovascular disease.
Boosting nitric oxide may provide other health benefits. Nitric oxide also functions as a negative regulator of the NLRP3 inflammasome. The NLRP3 inflammasome is a key component of the body's immune response, acting sort of like a molecular alarm system. When it misfires, or is chronically activated, excessive inflammation can ensue, leading to damage to healthy tissue or to various disease states. Nitric oxide can fine-tune the activation of this complex, ensuring that inflammation is kept in check.
Challenging Conventional Wisdom
Skin cancer prevention remains critical. But it does appear that moderate sun exposure could have a plethora of benefits for overall health and longevity, perhaps even surpassing the concomitant risk of melanoma. As the researchers conclude:
"Current public health messaging emphasises the hazards of UV exposure for skin cancer development. However, our study adds to growing evidence that the benefits of UV exposure on mortality outweigh the risks in low sunlight environments."
But what is moderate sun exposure? What is the appropriate dose for maximizing benefits while managing the risks of UV radiation? We can't really answer that yet, unfortunately, due to the limitations of this sort of research.
It is likely that context is important here. One thing that the researchers emphasize is that exposure patterns in higher UV environments, like Australia and parts of the US, may not be optimal for the UK and northern Europe, where the UV index is usually quite low. Future public health recommendations may need to be recalibrated with this geographical nuance taken into consideration.
From an individual perspective, you should probably take into account the UV index where you live (I personally use this app, which can tell you the UV index wherever you are at that very moment) when trying to strike this balance.
Random Trivia & Weird News
🐝 Oriental hornets metabolize alcohol so rapidly that they cannot get drunk.
A newly published experiment revealed that Oriental hornets can consume astronomical amounts of alcohol – even at 80% concentration – without showing any signs of intoxication or compromised health. For perspective, that's twice as strong as most hard liquors.
How do they do it? They have an incredibly efficient alcohol-processing system, powered by multiple copies of a gene that breaks down alcohol faster than any other known insect. This extraordinary ability likely evolved from their natural relationship with fermenting fruits and nectars, making them nature's best designated drivers.
Podcasts We Loved This Week
- Paddy Barrett: How to prevent heart disease. Via Siim Land Podcast.
- Joseph Uscinski: The psychology of conspiracy theories. Via Plain English with Derek Thompson.
Products We Like
Glycine powder
If you need some help adjusting to the upcoming time change, this might be worth a try. The amino acid glycine has been shown in some studies to accelerate sleep onset and improve sleep quality.
For example, a group of volunteers with insomnia were given glycine before going to bed in a sleep lab, where their sleep was measured via polysomnography. Compared to when they didn't take the glycine, taking the supplement boosted their sleep quality, and the participants transitioned into deep sleep sooner. Glycine may also help you perform better on days when you didn't get as much sleep as you wanted. When researchers had some people cut down on their sleep by 25%, and gave some of them glycine, the ones who received the supplement were significantly less fatigued and reported less sleepiness in the morning.
Interestingly, it appears to do this by triggering changes in body temperature. Glycine increases blood flow to the extremities, which in turn elicits a drop in core body temperature (for a more detailed explanation of how thermoregulation influences sleep, check out this blog). But you want to get at least three grams to achieve this benefit, which is why powder is the most efficient path.
humanOS Catalog Feature of the Week
How-to Guide: Chrononutrition
This week, we’d like to highlight our how-to guide for chrononutrition. When we talk about diet, we often fixate on what we are eating. But we are gradually realizing that when we eat also has a significant impact on our health and our daily performance.
This guide will help show you how to optimize your food timing, in alignment with the latest scientific research. If you’re looking for a bit of a deeper dive into the subject of nutrient timing and other aspects of circadian physiology, please refer to our Sleep and Body Clock OS Program.
Wishing you the best,
