Low Sunlight Exposure and Higher Risk for Pancreatic Cancer

Liam Davenport

May 01, 2015

People living in countries with low levels of sunlight have a substantially increased risk for pancreatic cancer, even after taking into account a number of factors associated with the disease, researchers conclude from a study published in the April 30 issue of the Journal of Steroid Biochemistry and Molecular Biology.

The team found that low exposure to ultraviolet B (UVB) irradiance, which is related to both latitude and the degree of cloud cover, is associated with a sixfold increased risk for pancreatic cancer.

"If you're living at a high latitude or in a place with a lot of heavy cloud cover, you can't make vitamin D most of the year, which results in a higher-than-normal risk of getting pancreatic cancer," said lead author Cedric F. Garland, DrPH, adjunct professor in the Department of Family and Preventive Medicine, University of California, La Jolla, in a press release.

"The importance of sunlight deficiency strongly suggests, but does not prove, that vitamin D deficiency may contribute to risk of pancreatic cancer," he added.

A previous study from the same team, published in 2010, showed that there was an inverse association between UVB and rates of incident pancreatic cancer, after taking into account a number of factors.

Since then, there have been a number of developments in the way in which UVB exposure can be assessed, and several publications have elucidated the link between serum vitamin D levels and the development of pancreatic cancer.

For the current study, the team obtained age-standardized pancreatic cancer incidence rates for 172 countries from the International Agency for Research on Cancer's GLOBOCAN 2008 database.

Data on energy intake from animal sources and alcohol consumption were obtained from the United Nations Food and Agriculture Organization, and the World Health Organization provided information on the prevalence of obesity, the sex-specific smoking prevalence, and per capita health expenditure.

Crucially, data from the NASAs International Satellite Cloud Climatology Project, which pertain to geographical variations in solar irradiance, allowed estimated UVB irradiance levels to be corrected for percentage cloud cover, inasmuch as heavy cloud cover does not transmit UVB.

The results demonstrate that, overall, there was a higher incidence rate of pancreatic cancer with lower cloud-adjusted UVB irradiance, such that residents of countries with low UVB irradiance were approximately six times more likely to have incident pancreatic cancer than those living in countries with high UVB irradiance (P < .0001 for males and females).

The associations remained significant after taking into account per capita health expenditure, the geographical distribution, and factors known to be associated with pancreatic cancer, such as diabetes, obesity, alcohol consumption, and smoking.

Interestingly, consumption of animal protein was positively associated pancreatic cancer in both sexes (P = .0190 in males; P = .0156 in females).

Given that this association was not an "artifact of residual confounding," the team suggests that there are number of potential mechanisms.

"One possibility is that high intake of protein or fat from foods of animal origin raises synthesis of cholecysokinin (CCK), a powerful peptide hormone produced in the bowel that stimulates synthesis of enzymes that dissolve proteins," they write.

In an interview with Medscape Medical News, Dr Garland explained that his research is important because pancreatic cancer is "so hard to study."

"It's so fatal that if you try to do a case-control study, where you interview the cases and then you interview matched controls, you can't do it, because they die very quickly," he said, adding, "You're given a short fuse."

"You're told you're going to die within 6 months or so, and you just don't want to cooperate. Any time they have they want to spend with their family, understandably, and not in some science study," he said.

Dr Garland continued: "It's also considered a rare disease ― too rare to study in a cohort study, because you'd have to have a huge cohort you'd have to study for some 10 to 20 years, and the National Cancer Institute is not willing to invest in that."

Given the strong association between UVB irradiance and pancreatic cancer risk, what about using vitamin D in an attempt to prevent or even treat pancreatic e cancer?

“Well, our theory is that UVB, leading to the synthesis of vitamin D, prevents pancreatic cancer, so it's totally consistent that people who would give vitamin D to pancreatic cancer patients would see a beneficial effect," he said, adding: "You see it for breast and colon cancer."

Dr Garland noted that there are a number of ongoing studies in both animal and human models on whether pancreatic cancer can be treated with vitamin D. He commented that there are not currently any "good" treatments for the disease, which kills approximately 25,000 Americans a year and is 95% fatal in 5 years.

"We can extend life maybe a year with chemotherapy, but people are miserable on chemotherapy, and it just gives them a year to say goodbye and get their affairs in order, but it isn't really a cure," he said.

"Vitamin D offers more of a potential," Dr Garland suggested, pointing out that it is "quite nontoxic." In his opinion, "It's time for people to start taking vitamin D to prevent this terrible disease."

Funding for this research came, in part, from the University of California, San Diego, Department of Family Medicine and Public Health.

J Steroid Biochem Mol Biol. Published online April 9, 2015. Abstract

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