Too much sunlight is bad for you. However, so is too little. New research from UC San Diego suggests a lack of sunlight is a risk factor for pancreatic cancer.
UCSD researchers recently published a study that found an inverse correlation between sun exposure and higher incidence rates for pancreatic cancer.
The study, performed by Adjunct Professors Cedric Garland and Edward Gorham, concluded that population centers located at higher latitudes had a higher incidence rate for pancreatic cancer than those located closer to the equator.
Garland, the main author of the study, explained that pancreatic cancer rates vary around the world.
“People who live in sunny countries near the equator have only one-sixth of the age-adjusted incidence rate of pancreatic cancer as those who live far from it,” Garland said.
The professors conducted the study by comparing national incidence/mortality rates of the potent cancer with a latitude-based ultraviolet B exposure score for each country. The professors obtained and calculated data for 172 countries, located at various latitudes in both the Northern and Southern hemispheres. What Garland found was a clear trend: countries with a higher incidence of pancreatic cancer were typically found at higher latitudes, with more cloud cover and therefore less exposure to UVB.
“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,” Garland said.
Though other confounding factors could have had an effect on pancreatic cancer incidence rates, Garland found that the correlation still held when taking these risk factors into account.
“The [correlation] did not go away when we adjusted for many factors, including health expenditures, body mass index, cigarette smoking and alcohol use,” Garland said.
Cohort studies cited by the paper have suggested that 25-hydroxyvitamin D – a modified form of vitamin D found in the body – is associated with a lower risk for pancreatic cancer. Vitamin D is readily synthesized by the body in the presence of ultraviolet radiation, specifically UVB.
“Solar UVB is the main source of vitamin D [for the human body] … It is estimated that 80 to 90 percent of vitamin D in circulation is from sunlight” Garland said, adding that vitamin D “and its metabolites have been linked to lower incidence and mortality of several cancers.”
UVB rays, while integral to the synthesis of vitamin D in the human body, can also lead to sunburn and potentially cancerous DNA degradation in skin cells. Sunscreen and avoiding excessive UV exposure have proven to decrease this risk. However, Garland warns that our efforts to protect ourselves from skin cancer are making us vitamin D deficient and potentially higher at risk for pancreatic cancer.
“Nowadays we make very little [vitamin D] because we usually wear clothes that cover 90 percent of our skin and wear sunscreens that totally prevent [UV absorption],” Garland said.
Garland recommends annual checkups to monitor vitamin D levels in our bloodstream.
“Everyone should have their 25-hydroxyvitamin D tested every February or March, when the concentration is lowest,” Garland advises, recommending a supplement in the event that levels are lower than the accepted 40 ng/ml.
“Adequate vitamin D [with calcium] has been shown in a randomized clinical trial to prevent four out of five cancers in postmenopausal women.”
It's possible to get vitamin D from foods like fatty fish (especially salmon and tuna), cheese, egg yolks and fortified products like milk, cereal and juices. But people need more vitamin D than can be provided by food, according to the researchers.
Another interesting observation form this study is that history of skin cancer conferred a 40% lower risk of pancreatic cancer, as compared with individuals who had no history of treated skin lesions.
So, people need sunlight, but in reasonable moderation.
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