by Craig Weatherby
We've reported these rapid developments in a sequence of articles painting the big picture on the relative cancer risks and rewards of moderate sun exposure, and summarizing the highly encouraging research results (The rewards seem to outweigh the risks very substantially... see sidebar titled "Our vitamin D archive").
Now,the results of a new data analysis add prevention of pancreatic cancer to the list of likely benefits that accompany adequate dietary intake of vitamin D.
While it constitutes only two percent of new diagnoses annually, pancreatic cancer is an unusually dangerous form. Out of the estimated 34,000 Americans who'll get pancreatic cancer this year, some 95 percent will succumb to its ravages.
The lack of an early-detection test, and the vagueness of early symptoms, make pancreatic cancer especially deadly. The most common symptoms include poor appetite, weight loss, stomach upset, and nausea. Disease-specific symptoms such as jaundice and itching generally fail to appear until patients are a few months from their mortality.
Only surgical removal (“resection”) of the cancer offers a substantial chance for a cure, and only 15-20 percent of people diagnosed with pancreatic cancer have a tumor localized enough to allow successful surgery.
The only other medical option is to combine chemo and radiation therapies, which does not offer a cure, but may shrink tumors enough to make surgery an option in some cases. While a cure of any cancer is always possible, a diagnosis of pancreatic cancer comes uncomfortably close to a death sentence.
Given that the prognosis is so grim, any evidence of a potential preventive measure would be very welcome. And that's been the case with the results of a new analysis of data from two large epidemiological studies.
Two universities team to examine diet and pancreatic cancer
This month's issue of the journal Cancer Epidemiology Biomarkers & Prevention contains the promising results of a study that offers real hope for nutritional prevention of pancreatic cancer.
Study leader Halcyon Skinner, Ph.D. has been deeply involved in the search for ways to prevent pancreatic cancer. He's published at least ten studies since 2001, probing the genetics of pancreatic cancer, and the preventive potential of agents like folic acid and aspirin.
Dr Skinner described the reasons for examining the anti-cancer potential of vitamin D in this context: “Because there is no effective screening for pancreatic cancer, identifying controllable risk factors for the disease is essential for developing strategies that can prevent cancer. Vitamin D has shown strong potential for preventing and treating prostate cancer, and areas with greater sunlight exposure have lower incidence and mortality for prostate, breast, and colon cancers, leading us to investigate a role for Vitamin D in pancreatic cancer risk."
The exciting findings his team published this month stem from a joint anaysis of personal diet and health information collected from the 46,771 men in the Health Professionals Follow-up Study and the 75,427 women in the Nurses' Health Study II.
The Skinner-Harvard team calculated the study participants' vitamin D intake from diet and supplements, based on responses to food frequency questionnaires. During 16 years of record keeping on the subjects in the two large cohort studies, 365 were diagnosed with pancreatic cancer.
Vitamin D associated with reduced pancreatic cancer risk
The US Recommended Daily Allowance for vitamin D is 400 international units (IU). And coincidentally, the results of the new data analysis indicate that this is enough to curb the risk of pancreatic cancer very substantially.
Dr. Skinner and his Harvard colleagues found that when people's daily vitamin D intake averages 300 to 449 IU, their risk of developing pancreatic cancer drops by 43 percent, compared with people who consume less than 150 IU.
And, the “sunshine vitamin” seems to serve up significant preventive benefits even in smaller doses. The subjects whose average daily intake fell between 150 and 299 IU were 22 percent less likely to develop pancreatic cancer, compared to those who reported the lowest intake.
When the researchers looked at intake of vitamin D from food alone (excluding supplemental sources), they found that people whose intake equaled or exceeded 300 IU per day had 33 percent less risk of pancreatic cancer, compared with those whose intake totaled less than 100 IU per day.
Thanks to the statistical power of the large sample size (122,198 doctors and nurses), Dr. Skinner and his colleagues were able to arrive at a pretty clear conclusion:
“In concert with laboratory results suggesting anti-tumor effects of Vitamin
D, our results point to a possible role for Vitamin D in the prevention and possible reduction in mortality of pancreatic cancer. Since no other environmental or dietary factor showed this risk [reduction] relationship, more study of Vitamin D's role is warranted.”
Like omega-3s, vitamin D seems a multi-faceted cancer-curber
Dr. Skinner and others believe the evidence indicates that vitamin D works to curb cancer in at least three ways:
- Reduces the formation of blood vessels in tumors (angiogenesis).
- Stimulates the mutual adherence of healthy cells.
- Enhances intercellular communication.
Dietary vitamin D must first be converted to an inactive form for storage, then into an “active” form as needed by the body to fight cancer or do anything else. It was thought that conversion of dietary vitamin D to its inactive stored form occurred only in the kidneys and liver.
But there is growing evidence that non-kidney cells can convert and store dietary vitamin D, which implies that it is more broadly available throughout the body to protect against cancer.
Even FDA finds vitamin D intake too low
In a recent journal article, scientists at the Food and Drug Administration's (FDA) Center for Food Safety and Applied Nutrition (CFSAN) reviewed recent actions to increase public awareness of the health importance of maintaining optimal levels of “circulating” (active) vitamin D and potential strategies to increase vitamin D intake (Calvo MS, Whiting SJ 2006).
Their motive was obvious, since, as they said, "...vitamin D may significantly reduce the risk of some chronic diseases such as osteoporosis, cardiovascular disease, diabetes and some cancers, particularly in the elderly and blacks."
The FDA researchers came to several key conclusions:
- “Clinicians and educators are encouraged to promote improved vitamin D intake and status… This will… largely depend on combined efforts to judiciously fortify our food supply and to develop individual supplementation protocols...”
- The cost to fortify food or supplements with vitamin D is relatively inexpensive compared with developing drugs used to treat or prevent chronic diseases; moreover, there is significant potential for broad health benefits in the reduced risk and prevention of multiple chronic diseases.”
- “Growing evidence supports a low risk of toxicity with vitamin D use in fortification or supplementation…"
Of course, your body makes lots of vitamin D when sun rays hit the skin, but most vitamin D advocates believe it is smart to take out insurance in the form of supplements and D-rich foods.
We should note (see “Vitamin D superstars” sidebar above) that sockeye salmon is uniquely rich in vitamin D, and that other salmon and oily ocean fish (e.g., tuna, sardines, halibut, mackerel, sablefish) are the next best food sources.
- Skinner HG, Michaud DS, Giovannucci E, Willett WC, Colditz GA, Fuchs CS.Vitamin D Intake and the Risk for Pancreatic Cancer in Two Cohort Studies. Cancer Epidemiol Biomarkers Prev. Vol. 15, 1688-1695, September 2006.
- Stobbe M. New benefit seen in vitamin D: Study finds it can halve risk of pancreatic cancer. Associated Press, September 15, 2006.
- Schwartz GG, Eads D, Rao A, Cramer SD, Willingham MC, Chen TC, Jamieson DP, Wang L, Burnstein KL, Holick MF, Koumenis C. Pancreatic cancer cells express 25-hydroxyvitamin D-1 alpha-hydroxylase and their proliferation is inhibited by the prohormone 25-hydroxyvitamin D3. Carcinogenesis. 2004 Jun;25(6):1015-26. Epub 2004 Jan 23.
- Ohlsson B, Albrechtsson E, Axelson J. Vitamins A and D but not E and K decreased the cell number in human pancreatic cancer cell lines. Scand J Gastroenterol. 2004 Sep;39(9):882-5.
- Albrechtsson E, Jonsson T, Moller S, Hoglund M, Ohlsson B, Axelson J. Vitamin D receptor is expressed in pancreatic cancer cells and a vitamin D3 analogue decreases cell number. Pancreatology. 2003;3(1):41-6.
- Calvo MS, Whiting SJ. Public health strategies to overcome barriers to optimal vitamin D status in populations with special needs. J Nutr. 2006 Apr;136(4):1135-9.