Sunscreen (non)sense

A recent comment on the Risk Science Center Facebook page asked whether we could help make sense of this article, posted on the website a few days ago:

Scientists Blow The Lid on Cancer & Sunscreen Myth, July 5 2014

The article cites a piece in The Independent, which in turn reports on a paper published in May in the Journal of Internal Medicine.  And it and makes the startling statement that

Researchers concluded that the conventional dogma, which advises avoiding the sun at all costs and slathering on sunscreen to minimize sun exposure, is doing more harm than actual good.

What does the original study show?

The original paper by Lindquist et al. (Avoidance of sun exposure is a risk factor for all-cause mortality: results from the Melanoma in Southern Sweden cohort, 2014, J. Internal Medicine, DOI:  10.1111/joim.12251) recorded mortality rates from all causes in a group of 29,518 Swedish women between the early 1990′s and the early 2010′s, and related these to sun exposure evaluated using four criteria (more on this below).

Overall, 8.6% of the women (2545) died over the course of the 20 year study.  What caught the researchers’ attention in particular though was that women who did not actively seek sun exposure were slightly more likely to die.  Over a 15 year period, the researchers found that 96% of women who most actively sought sun exposure were still alive, compared to a survival rate of 95% for women who were moderately active in seeking sun exposure, and a survival rate of 93% for those who did not actively seek sun exposure.

This difference of 3% in survival rate between sun seekers and sun avoiders is small, but given the large number of women involved, it is statistically significant for this group of women, and the criteria of sun avoidance and seeking used.  The study did not look at the use or otherwise of sunscreen.

The authors speculate quite reasonably that the results could be associated with vitamin D production.  Vitamin D is essential to good health, and is mainly produced by the body through exposure to ultraviolet light of the same wavelength that can also cause DNA damage in skin cells.  So it’s not surprising that there are tradeoffs occurring with sun exposure that simultaneously protects and threatens health.  In an accompanying editorial, journal editor N. G. Jablonski notes

The biggest questions to emerge from the Lindqvist et al. study surround the nature and activity of the compounds produced by sun exposure and what happens in sun avoiders when these compounds are absent or present only at low levels. If this is primarily a vitamin D effect, then remedial measures such as additional food fortification or recommendations for vitamin supplementation can be implemented relatively easily, with no risk of additional skin cancers. (N. G. Jablonski (2014) Journal of Internal Medicine, DOI: 10.1111/joim.12248)

Getting the facts right

In other words, this is not a study that “blows the lid on the sunscreen and cancer myth”, but one that indicates that it may be important to get the balance right between enough sun exposure to keep vitamin D levels up, and little enough exposure to avoid skin cancer.  In fact, the paper’s authors start out by saying:

Ultraviolet (UV) radiation from the sun is known to heighten the risk of developing malignant melanoma (MM) of the skin. This condition is primarily responsible for increased mortality due to UV radiation exposure.

It’s also important to note that the questions used to determine sun seeking behavior were quite specific:

1.  How often do you sunbathe during the summertime? (never, 1–14 times, 15–30 times, >30 times);
2.  Do you sunbathe during the winter, such as on holiday to the mountains? (no; 1–3 days, 4–10 days; >10 days);
3.  Do you use tanning beds? (never; 1–3 times per year; 4–10 times per year; >10 times per year); and
4.  Do you go abroad on holiday to swim and sunbathe? (never; once per 1–2 years; once per year; two or more times per year)

Four answers of no, none or never, were considered to indicate the respondent did not actively seek sun exposure, while four answers greater than no, none or never, were considered to indicate high sun-seeking activity.  The study did not ascertain whether UVA and UVB protection was used by sun seekers.  And it did not look at broader social, economic  or physiological factors that might have led to 1352 of the 29,518 women in the survey not sunbathing or using tanning beds.

A sunscreen smokescreen

The implications of the study are that some sunlight is good for you – probably due to the vitamin D and possibly other chemicals that it helps the body generate, and that a lifestyle that is associated with sunbathing may be slightly beneficial – especially if you are Swedish.  It is inconclusive as to the risks or otherwise of developing skin cancer and sun exposure.  And it most certainly does not suggest that not using sunscreen is a good idea!

Updated July 13: Added headings