Can High Sun Exposure Lead To Less Cancer And Cardiovascular Deaths?
High sun exposure is associated with striking reductions in cancer and cardiovascular deaths, at the expense of only small increases in fatal skin cancers
I was intrigued by this paper published as a pre-print recently:
The paper analyses data collected from over 400k individual participants of the UK Biobank study.
What is the UK Biobank?
You can read about the history of the UK Biobank here. In brief, this initiative was established in 2003 via a collaboration between Wellcome and a number of public bodies.
Its aims were – by means of long-term follow and analysis of a huge population of citizens (>500k) – to provide a large-scale, open-access resource for identifying the causes of complex diseases in middle and old age.
Each volunteer underwent an initial detailed in-person assessment. Various cohorts were then invited for follow-up assessments which involved a variety of measurements. Each volunteer consented to their individual records being traced long-term via the NHS records system, and cancer and death registries.
Here’s a summary of the planned follow-up measurements:
What did the authors do in this study?
In the particular paper I’m referencing here, the investigators (all from the University of Edinburgh) sought to examine the relationship between sun exposure and health outcomes.
The scientists conceived a new index of UV exposure which they called the Sun-BEEM (Behavioral and Environmental Exposure Model–UV) score, which ranged from 0 to 4, as follows:
(Residential UV exposure was calculated according to the participant’s home address.)
The total points scored were translated into the following categories:
- Low UV: Total score of 0–1
- Medium UV: Total score of 2
- High UV: Total score of 3–4
They provide good evidence that the Sun-BEEM score did indeed reflect sun exposure:
- a strong statistical correlation between the Sun-BEEM categories and serum Vit-D levels (ie a dose-response relationship).
- a “biological gradient” of increased incidence for keratinocyte (non-melanoma) skin cancers, which are known to be primarily caused by UV radiation.
Main findings
Below are the key outcomes. The low UV exposure group is the index group against which the other categories are compared, so, for example, High UV exposure was associated with a 16 percent lower risk of dying (all cause) compared to low UV expsore.
Key results
- The Net Survival Benefit: While higher sun exposure increased the incidence of non-fatal skin cancers (like basal cell carcinoma), it was associated with a much larger reduction in deaths from heart disease and internal cancers.
- Cardiovascular Health: The data showed that high UV exposure was most beneficial for heart health, with the researchers suggesting this is due to non-vitamin D pathways like the release of nitric oxide which lowers blood pressure.
- Non-Skin Cancer: Higher exposure levels consistently correlated with lower rates of death from “internal” cancers (such as lung, colorectal, or breast cancer).
- Skin Cancer Paradox: Interestingly, while high UV exposure increased the number of skin cancer diagnoses, it did not lead to a statistically significant increase in skin cancer deaths compared to the low-exposure group.
The authors then modelled what the outcome would have been had the entire cohort followed a High UV lifestyle vs one in which the sun is avoided.
The results are striking:
What did the authors adjust for in order to “level the playing field”?
An obvious criticism of an observational study such as this is that UV exposure could simply be a proxy for other habits / lifestyle factors which are in themselves beneficial to health.
For example, the people with high UV exposure could be those who live in the (relatively) wealthier Southern parts of the UK, where health (and healthcare) is better than in the North.
Similarly, going outside a lot (and having more sun exposure) could simply be an indicator for taking more exercise. In order to account for such factors, the authors employed a model which included adjustments for what appears to be a fairly comprehensive list of possible confounders:
It must be stressed, however, that a potential problem with all such observational studies is that there may be unknown confounders which (because they are unknown) haven’t been adjusted for.
Observational studies do, in essence, suggest correlative relationships and it is therefore often said that only a randomised interventional study (where one group is treated one way and compared to another treated differently) can prove causation.
However, this purist approach doesn’t account for the fact that it isn’t practically possible (let alone ethical) to conduct trials which test all credible hypotheses. Sometimes, observational data IS sufficient to advance certain hypotheses – for example Richard Doll’s work on the link between smoking and lung cancer.
It should also be pointed out that the much-trumpeted and so-called “real-world” studies used in support of the efficacy of the “covid vaccines” (especially boosters) were also observational in nature; they compared a group with a propensity to choose to receive an an injection with another group which didn’t, there being no random allocation involved.
These two groups are fundamentally different in a number of ways.
One way of attempting to correct for such differences between groups is to statistically adjust for them. As described above, in the case of this UV exposure paper a fairly comprehensive range of factors was considered.
Another thing to look at which bolsters the case for causation is whether there are other, biological plausible, observations which support the claims being made.
Benefits were validated by other plausible biological pathways
The authors showed changes in circulating proteins in the blood that link UV exposure to lower mortality. (This was carried out in a subset of ~44k subjects.)
The above findings suggest that the health benefits are driven by mechanisms largely independent of the vitamin D pathway. However, these measurements were only made once, at the outset; to establish a causal role future studies would need to look at changes over time.
In conclusion
This study provides some evidence that increased sun exposure has substantially more health benefits than downsides.
The benefit of reducing sun exposure – a reduction in fatal skin cancers – is really quite marginal, yet a mighty edifice has been built around avoiding the sun while lathering ourselves with sun screen.
Perhaps it is time to reasses this approach.
See more here substack.com
Some bold emphasis added
Header image: Healthline