One of two new studies in the 2 February issue of the Journal of the National Cancer Institute found that sun exposure may increase chances of survival from the deadly skin cancer malignant melanoma. Solar radiation is a major risk factor for melanoma.
Another trial out this week suggests that sun may also reduce risk of non-Hodgkin lymphoma.
Sun's benefit could be down to the vitamin D made by sun-exposed skin, believe researchers.
Vitamin D has previously been associated with a protective effect against cancer. Last year, UK researchers found that women with certain versions of the vitamin D receptor gene are almost twice as likely to develop breast cancer than women with other versions of the gene.
It has also been linked to reduced risk of colon cancer.
In the new study Marianne Berwick of the University of New Mexico in Albuquerque and colleagues conducted a population-based, case-control study of more than 500 patients who had been diagnosed with melanoma in the late 1980s.
The incidence of and mortality from melanoma have been increasing over the last 50 years in all developed countries with large Caucasian populations. But survival has also improved, suggesting that increasing sun exposure increases melanoma survival in addition to melanoma incidence.
However, increased early detection of melanoma might also explain the increased survival.
The US team report that three measures of sun exposure-sunburn, high intermittent sun exposure, and solar elastosis (an indicator of the skin's sun damage)-and a personal history of skin awareness (a measure of early detection) were all inversely associated with death from melanoma.
Melanoma patients with higher levels of sun exposure or skin awareness were less likely to die.
In addition, both solar elastosis and skin awareness were independently associated with increased survival from melanoma, even after adjusting for certain melanoma characteristics, such as lesion thickness and location.
The authors conclude that sun exposure is associated with increased survival from melanoma.
"It would be reasonable to speculate... that the apparently beneficial relationship between sun exposure and survival from melanoma could be mediated by vitamin D," Berwick and colleagues write.
"However, an alternative hypothesis is that sun exposure induces less aggressive melanomas by inducing melanization and increasing DNA repair capacity, both of which might reduce further mutational changes in a melanoma. Which, if either, hypothesis is more plausible remains to be determined."
Ultraviolet (UV) radiation and sun exposure has also been thought to be partly responsible for the worldwide rise in non-Hodgkin lymphoma.
To investigate this hypothesis, Karin Ekström Smedby, of the Karolinska Institute in Stockholm, and colleagues conducted a population-based, case-control study in Denmark and Sweden using history of UV exposure and other risk factors for lymphoma from more than 3,000 lymphoma patients and a similar number of control subjects.
They found that increased exposure to UV radiation through sunbathing and sunburns was associated with a decrease, rather than an increase, in the risk of non-Hodgkin lymphoma. Increased UV exposure was also associated, although more weakly, with a decreased risk of Hodgkin lymphoma.
"[These] results suggest an inverse association between UV light exposure and non-Hodgkin lymphoma risk," Smedby and colleagues write. "However, before this association can be considered causal we need further confirmatory data from other epidemiologic studies and, ideally, a better understanding of possible biologic mechanisms," including UV-induced systemic immune modulation and the photo-initiation of vitamin D production.
In an editorial, William J. Blot of the International Epidemiology Institute in Rockville, Maryland and colleagues discuss how the results of these two studies provide new evidence that sunlight may have a beneficial influence on both cancer incidence and outcome.
They hypothesize that vitamin D may be a critical mediator in the relationship between sunlight and cancer.
"In view of the major potential public health consequence of these results, further studies of sunlight and the vitamin D connection to cancer are certainly warranted," they conclude.