Jun 23, 2014
By Shira Klapper, Senior Writer/Editor
For years now, the age-old advice to “drink your milk” has been supported by numerous studies showing that people who consume more calcium, vitamin D, and dairy products have a lower risk of developing colorectal cancer. But until now, no one had studied whether those same nutrients confer benefits to people after they’ve been diagnosed with the disease. Now an article in the Journal of Clinical Oncology (JCO), published online ahead of print, June 23, reports on the first-ever study to tackle this question. The study found that among patients with non-metastatic colorectal cancer, those who consumed more calcium and milk after their diagnosis had a lower rate of death from all causes. These same benefits were not seen in those who consumed more vitamin D. In addition, the amount of calcium, vitamin D and dairy consumed before diagnosis had no effect on the rate of survival.
“Other survival studies have looked at pre-diagnosis calcium and at the levels of the circulating form of vitamin D and the impact on survival,” said senior author, Peter T. Campbell, PhD. “This study, however, is the first to look at whether the levels of calcium, dairy and vitamin D patients consume after their diagnosis affects their overall survival.” “Overall survival,” refers to survival not only from colorectal cancer, but from other causes of death as well.
The study, “Calcium, Vitamin D, Dairy Products, and Mortality among Colorectal Cancer Survivors: the Cancer Prevention Study-II Nutrition Cohort,” followed a selected group of 181,293 people who were participating in the Cancer Prevention Study II (CPS-II) Nutrition Cohort and who were free of colorectal cancer at baseline (the CPS-II study has a total of 184,000 participants). In 1992 and 1993, those 181,293 participants were asked to report on their nutritional intake via a modified version of the Block Food Frequency Questionnaire (FFQ); data on nutritional intake were updated in 1999 and 2003 using a modified Willett FFQ. To assess any new cancer diagnoses, follow-up questionnaires were sent starting in 1997 and then once every two years.
In 2009, the researchers looked at the group of 181,293 people to see who had been diagnosed with colorectal cancer in the intervening 17 years since the study began. Among this group, 2,284 were found to have disease, after excluding participants based on factors such as unconfirmed diagnoses or missing tumor stage.
Post-diagnosis levels of calcium and milk make a difference
Upon analyzing those 2,284 participants who developed colorectal cancer, the researchers found that pre-diagnosis dietary levels of calcium, dairy, and vitamin D did not affect overall survival. The researchers then analyzed how post-diagnosis levels of calcium, dairy, and vitamin D affected survival. For this measure, the researchers had data only on 1,111 of the 2,284 participants; many participants had either died before they could fill out a post-diagnosis nutritional questionnaire or were diagnosed after 2003 (when dietary data were last updated).
The study found that pre-diagnosis calcium and milk intake—as reported by participants in the 1992/1993 baseline questionnaires—had no effect on overall mortality among those who developed colorectal cancer. However, the more the patients consumed these same nutrients after colorectal cancer diagnosis, the lower their overall mortality rate. In addition, the study found that vitamin D intake, both before and after diagnosis, had no effect on post-diagnosis survival. Interestingly, the study also found that those who took 250 milligrams or more per day of calcium supplements—that is, calcium taken in vitamin, not food form—had a significantly higher risk of overall mortality.
The mechanisms at play
Dr. Campbell described several theories that might explain why consuming calcium and dairy products protect against mortality.
“From lab-based analyses, we know that calcium can bind to bile and fatty acids, which would lower toxicity in the colon and may prevent future recurrences and death from the disease,” said Dr. Campbell. “In addition, calcium has been shown in in vitro work to slow down colonocyte proliferation, that is, the growth of colon cells, which would also include colon cancer cells. Calcium can also induce apoptosis, which is early cellular death.”
Dr. Campbell also suggested a possible explanation for why vitamin D was found to have no effect on survival.
“Going into this study we thought vitamin D had as strong of a chance of being associated with lower mortality as did calcium or milk,” said Dr. Campbell. “One explanation for why it did not have the same association is that it is circulating vitamin D, and not just the amount consumed, that is more relevant to survival. And circulating vitamin D is also influenced by sun exposure, not just diet.”
Commenting on the found connection between supplemental calcium and overall mortality, Dr. Campbell stated that these results are consistent with previous research showing an association between intake of supplemental calcium and increased risk of death, mainly due to cardiovascular events.
Dr. Campbell noted that more research is needed before colorectal cancer doctors advise their patients to eat a bowl of ice cream after every meal and wash it down with a calcium-packed spinach drink.
“These results, just like any other first results, need to be replicated before we start seeing changes in dietary and clinical guidelines for cancer survivors,” said Dr. Campbell. “We need to see the same positive results for calcium and dairy products either in additional observational studies or preferably in randomized controlled trials [which assign specific diets to different groups and observe them over time]. If we then see that total calcium and milk intake are associated with lower risk of all-cause mortality, patients might be encouraged to drink more milk and eat more foods containing calcium.”
Peter T. Campbell, PhD, is the Director of the Tumor Repository at American Cancer Society, Inc.
Click here to read the abstract.
Click here to read the PDF.
Yang, B, McCullough, ML, Gapstur, SM, et al. Calcium, vitamin D, dairy products, and mortality among colorectal cancer survivors: the Cancer Prevention Study-II Nutrition Cohort. J Clin Oncol. 2014. Published online ahead of print 6.23.2014.
The Exclusive Coverage series on ASCO.org highlights selected research from JCO with additional perspective provided by the lead or corresponding author.
@ 2014 American Society of Clinical Oncology