Vitamin D, known as the “sunshine vitamin”, has been found to have many health benefits but is mainly associated, in conventional medicine, with keeping bones strong. Up until now, most studies have been inconsistent concerning the value of vitamin D in safeguarding against certain cancers such as colorectal cancer. Let’s take a look at a very current and promising study concerning vitamin D and colorectal cancer.
Vitamin D International Study
The results of a current large international study provide the greatest evidence so far that vitamin D may be undeniably protective against colorectal cancer. But there’s more. The study also shows that a Vitamin D deficiency may actually increase the risk of colorectal cancer. This study authored by scientists from the American Cancer Society, the Harvard T.H. Chan School of Public Health, the U.S. National Cancer Institute, and more than 20 other medical centers and organizations appeared Thursday, June 14, 2018, in the Journal of the National Cancer Institute.
The study merged findings from 17 previous studies along with 12,813 adults in the U.S., Europe, and Asia. Altogether these studies looked at 5,706 people with colorectal cancer and 7,107 people of comparable age and race who didn’t have cancer. The menopausal status of participating women was also taken into account. A single, widely accepted assay and laboratory were used for new vitamin D measurements and calibration of existing vitamin D measurements. “In the past, substantial differences between assays made it difficult to integrate vitamin D data from different studies,” explained Regina G. Ziegler, Ph.D., a National Cancer Institute epidemiologist and co-senior author on the article. “This calibration approach enabled us to systematically explore risk over the broad range of vitamin D levels seen internationally.” To determine what role vitamin D might be playing, researchers looked at participants’ blood samples collected in the years before their cancer diagnosis. Established risk factors for colorectal cancer which included smoking, low physical activity, and high body mass index were also examined.
Marji McCullough, a nutritional epidemiologist with the American Cancer Society and a co-author of the study says: “For both men and women, deficient levels of vitamin D were associated with a 30 percent increased risk of colorectal cancer. Those who had higher circulating blood levels of vitamin D, above the range deemed ‘sufficient,’ had a 22 percent lower risk.”
The current recommendations for vitamin D supplementation are based exclusively on studies indicating that it does preserve bone health. “Our findings suggest what’s optimal for bone health may not be optimal for colorectal risk reduction,” McCullough says, which could mean higher doses are absolutely needed to prevent cancer.
Vitamin D Lowers Risk of Colorectal Cancer in Women
McCullough says that “A particularly provocative finding of the study is the relatively strong correlation between higher blood levels of vitamin D and lower risk of colorectal cancer in women. We don’t know why. One suggestion is that there is some interaction between vitamin D and female hormones. Or it’s possible vitamin D prevents cancer by reducing the proliferation of tumor cells or by stopping their growth and ‘actually killing those cells.'”
While studies like this do not prove cause and effect, they do show that there could be a connection between the levels of vitamin D circulating through the body and cancer. Still, the paper authors write that “the results substantially strengthen the evidence, previously considered inconclusive, for a causal relationship” between low vitamin D levels and colorectal cancer.
McCullough adds: “Another interesting observation in the study was that beyond a certain level, increasingly higher amounts of vitamin D in the blood had no additional benefit. At the highest levels above what is considered ‘adequate,’ there was no further reduction in risk. In other words, ‘more is not necessarily better.'”
McCullough’s bottom-line message: “Don’t race out and buy high doses of vitamin D ‘just in case.’ Overdoing it can be toxic. Taking too much vitamin D can cause kidney stones and, in very rare cases, death.”
The issue of whether vitamin D supplements should be used at all to prevent colorectal cancer is still up in the air. “The key question now is whether intervening with people who have low levels of vitamin D can make a difference,” says Dr. Jeffrey Meyerhardt, director of the Gastrointestinal Cancer Center at Dana-Farber Cancer Institute in Boston, who was not involved in the study.
The study was limited to looking at the level of vitamin D in people’s blood and did not evaluate whether the addition of vitamin D through food, sunlight or supplements made a difference in cancer risk.
Another large study involving more than 25,000 patients is currently underway at Brigham and Women’s Hospital in Boston. Its objective is to find out whether taking vitamin D supplements might reduce the risk of numerous cancers as well as heart disease and stroke. Dr. Meyerhardt says that answers may be available in the coming year. In the meantime, he suggests people talk with their health care provider about having a blood test to measure vitamin D levels. If you’re starting in the deficient range, he says, some doctors might prescribe high doses, to be taken each week for a month or two, and then prescribe lower, maintenance levels.
McCullough says it is generally recommended that adults have a daily intake of 600 international units of vitamin D up to age 70 and men and women over age 70 should increase their uptake to 800 IUs daily. People should talk with their doctors because different individuals have different needs. It depends on where you live and what race you are because darker skin tends to absorb less vitamin D. Sun, age, genetics, and weight also play a role in how the body processes vitamin D.
In Conclusion
Your vitamin D levels are important and should be checked one to two times yearly. While vitamin D can be obtained from vitamin D-rich foods such as egg yolks, salmon, trout, swordfish, tuna, and sardines as well as many foods fortified with vitamin D including cow’s milk, almond milk, soy milk, some cereals, and some orange juices, adequate amounts of vitamin D do not usually come from diet alone. Since multivitamins contain relatively low levels of vitamin D, taking an organic Vitamin D supplement is usually necessary to meet recommended doses. It’s very important to have your vitamin D levels checked before assuming they are deficient. Talk with a knowledgeable healthcare practitioner who will be able to order testing and determine if a vitamin D supplement is necessary for you.
RESEARCH
Marjorie L McCullough, Emilie S Zoltick, Stephanie J Weinstein, Veronika Fedirko, Molin Wang, Nancy R Cook, A Heather Eliassen, Anne Zeleniuch-Jacquotte, Claudia Agnoli, Demetrius Albanes, Matthew J Barnett, Julie E Buring, Peter T Campbell, Tess V Clendenen, Neal D Freedman, Susan M Gapstur, Edward L Giovannucci, Gary G Goodman, Christopher A Haiman, Gloria Y F Ho, Ronald L Horst, Tao Hou, Wen-Yi Huang, Mazda Jenab, Michael E Jones, Corinne E Joshu, Vittorio Krogh, I-Min Lee, Jung Eun Lee, Satu Männistö, Loic Le Marchand, Alison M Mondul, Marian L Neuhouser, Elizabeth A Platz, Mark P Purdue, Elio Riboli, Trude Eid Robsahm, Thomas E Rohan, Shizuka Sasazuki, Minouk J Schoemaker, Sabina Sieri, Meir J Stampfer, Anthony J Swerdlow, Cynthia A Thomson, Steinar Tretli, Schoichiro Tsugane, Giske Ursin, Kala Visvanathan, Kami K White, Kana Wu, Shiaw-Shyuan Yaun, Xuehong Zhang, Walter C Willett, Mitchel H Gail, Regina G Ziegler, Stephanie A Smith-Warner; Circulating Vitamin D and Colorectal Cancer Risk: An International Pooling Project of 17 Cohorts, JNCI: Journal of the National Cancer Institute, djy087, https://doi.org/10.1093/jnci/djy087
