• Too much sun is still bad for you

    In May, a study was published that showed that women who got no sun had higher all cause mortality than those who were out in the sun. This study was presented as a refutation to those who have been cautioning about the danger of sun exposure. But it’s not nearly as life-changing a study as many are pitching it to be. Let’s start with the abstract:

    BACKGROUND: Sunlight exposure and fair skin are major determinants of human vitamin D production, but they are also risk factors for cutaneous malignant melanoma (MM). There is epidemiological evidence that all-cause mortality is related to low vitamin D levels.

    METHODS: We assessed the avoidance of sun exposure as a risk factor for all-cause mortality for 29 518 Swedish women in a prospective 20-year follow-up of the Melanoma in Southern Sweden (MISS) cohort. Women were recruited from 1990 to 1992 and were aged 25 to 64 years at the start of the study. We obtained detailed information at baseline on their sun exposure habits and potential confounders. Multivariable flexible parametric survival analysis was applied to the data.

    RESULTS: There were 2545 deaths amongst the 29 518 women who responded to the initial questionnaire. We found that all-cause mortality was inversely related to sun exposure habits. The mortality rate amongst avoiders of sun exposure was approximately twofold higher compared with the highest sun exposure group, resulting in excess mortality with a population attributable risk of 3%.

    CONCLUSION: The results of this study provide observational evidence that avoiding sun exposure is a risk factor for all-cause mortality. Following sun exposure advice that is very restrictive in countries with low solar intensity might in fact be harmful to women’s health.

    Lots of qualifiers in there, but the take home reality was that there was a significantly higher all-cause mortality rate in those who avoided the sun altogether. Now for the caveats:

    1) The absolute rate difference was 3% to 1.5%. Yes, the headlines say DOUBLED, but that’s relative, and we all know the difference, right?

    2) Even this study found that sun exposure was significantly linked to melanoma risk. That’s still true.

    3) Observational studies like this are going to be confounded. Is it that hard to imagine that active people are more likely to be exposed to sun than totally sedentary people?

    4) There’s a lot of talk from this about vitamin D levels, and how this study shows that lack of sun leads to low vitamin D, and that’s a problem. Wow. First of all, the links of “low vitamin D” to death is a stretch. But even if you skip past that, there’s nothing in this study – and I mean nothing – that specifically looks at vitamin D. There’s no measurement of vitamin D. No way to know if anyone is vitamin D deficient. No vitamin D variables at all.

    5) This is not an RCT. There’s no causality here. There are, however, RCTs showing that sunscreen prevents melanoma and skin aging.

    I believe that everyone, including kids, should be outside playing. There are many, many pics of me doing so in my Instagram account. But I use sunscreen, and I use it liberally. Nothing in this study will change my mind about that.

    @aaronecarroll

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