A month ago I showed you my public comment on the Surgeon General’s anticipated statement on ultraviolet light (UV) and skin cancer. I made the argument that UV has both positive and negative effects on health. These effects depend upon skin color in that, compared to those with darker skin, those with lighter skin have the benefit of much higher vitamin D levels and the risk of much higher rates of skin cancer. Given the diversity of skin colors in the U.S., I suggested public health policy should address the needs of people of all skin colors rather than addressing the needs of light-skinned people while ignoring the vitamin D needs of people of color.
My statement included 23 references, but since then another study has been published and noted on our website here that would have fit right in with the others cited in my comment:
Brondum-Jacobsen P, Nordestgaard BG, Nielsen SF, Benn M. Skin cancer as a marker of sun exposure associates with myocardial infarction, hip fracture and death from any cause. Int J Epidemiol. Sep 13 2013.
This study looks at the health effects of high-levels of UV exposure by using skin-cancer itself as the marker for high UV exposure. The study used hip fractures, heart attacks, and death from any cause as outcome measures. The idea was to test the hypothesis that those with higher levels of UV exposure, as determined by a skin cancer event, would have lower levels of heart attacks, hip fractures, and deaths from any cause. Relationships between these outcomes using vitamin D status as the marker for UV exposure have been reported previously in the literature. Using skin cancer itself as the marker for UV exposure, however, concentrates the mind on both the negative and positive health impacts of UV.
The researchers had access to a magnificent data set – the entire population of Denmark above 40 years of age from 1980 through 2006. To create the data set the researchers combined data from:
- the Danish Civil Registration System, which included births, deaths, and moves into or out of the country
- the Danish Cancer Registry, which included information on 98% of the cancer cases in Denmark
- the Danish Patient Registry and the Danish Causes of Death Registry, which included data on hip fractures, heart attacks, and death from any cause
- and Statistics Denmark, which provided demographic information.
The cancer data included codes to separate basal cell and squamous cell carcinoma (non-melanoma skin cancer), which typically do not result in death, from melanoma, which, untreated, typically does. “Constant and prolonged sun exposure patterns cause non-melanoma skin cancer, whereas overexposure as a child and high intensity intermittent sun exposure primarily cause cutaneous malignant melanoma,” the researchers say.
Overall, the data set included 4.4 million individuals, 1.6 million deaths, 328,000 diagnoses of heart attacks, 129,000 of hip fractures, 129,000 of non-melanoma skin cancers, and 22,000 of melanoma.
The researchers analyzed the data several different ways, but the results were similar in all cases. Figure 1 shows the cumulative incidence of hip fractures, heart attacks, and death as a function of age in individuals who also had a diagnosis of non-melanoma skin cancer. As you can see in the graphs, those who were diagnosed with non-melanoma skin cancer also had fewer hip fractures, fewer heart attacks, and lived longer.
While the researchers were very careful to limit the implications of their data (“Causal conclusions cannot be made from our data. A beneficial effect of sun exposure per se needs to be examined in other studies.”), what we’re talking about here is whether it is ethical to continue existing global health policy recommendations that people of all skin colors should limit UV exposure.
According to the American Cancer Society, in the U.S. skin cancer deaths make up just 2% of all cancer deaths. In this data set, a heart attack is about 15 times more likely than melanoma. The policy experts who insist that UV should be limited have no evidence showing that limiting UV is beneficial to health in any way other than reducing skin cancer. Meanwhile, here we have a study that shows that even in a population where 90% of the individuals have a light skin color, and even among individuals who have had skin cancer, increased levels of UV exposure are related to better health.