Vitamin D and Cancer Prevention: What’s the Evidence Behind the Hype?
In November 2010, the Institute of Medicine (www.iom.edu) issued a report on dietary intake of calcium and vitamin D. This was prompted by new data on various skeletal and non-skeletal health benefits (including cancer prevention); in particular, those associated with vitamin D supplementation. The report's final recommendations include a modest increase in the recommended daily intake of vitamin D from 400 international units (IU) to 600 IU with an upper limit of intake at 4000 IU. However, the authors caution that "data do not provide compelling evidence that calcium or vitamin D is causally related to extra-skeletal health outcomes or that intakes greater than those established in the daily recommended intake have benefits for health".
The IOM report considered all potential health benefits in general, but did not hone in on specific diseases. In fact, the authors acknowledged that more studies are needed to fully understand the biology and clinical benefit of vitamin D supplementation for various conditions. But what is the existing evidence of vitamin D benefits specifically for prevention of cancer?
Historically, the beneficial effects of vitamin D on cancer were first described in colorectal cancer. Investigators noted a latitudinal north-south gradient in the United States for colon cancer (Garland & Garland, 1980). This gradient was thought to be due to sunlight exposure as 90% of circulating vitamin D is synthesized by solar UVB light. Many subsequent studies of vitamin D and colorectal cancer have confirmed a protective effect. The greatest protection appears to be achieved with higher vitamin D blood levels associated with higher daily intake of vitamin D3 (cholecalciferol). An ongoing clinical trail called the VITAL study is investigating daily intake of 2000IU vitamin D3 on cancer development.
A similar north-south gradient was noted for breast, prostate, kidney, endometrial, ovarian and lung cancers. Similar to the studies in colorectal cancer, higher blood levels of vitamin D are associated with decreased risk of breast cancer. Prostate cancer also appears to benefit from vitamin D including treatment of existing tumors. At present, the existing data for kidney, endometrial, ovarian and lung cancers are less robust but studies are ongoing. In contrast, studies in pancreatic cancer have suggested that high levels of vitamin D might increase risk of pancreatic cancer in at-risk populations (especially smokers). Further study is needed to resolve some of these conflicting results in pancreatic cancer.
While there is still debate about the science of vitamin D supplementation, growing perception of benefits by both physicians and the public has increased markedly in the last few years. The New York Times reported that orders for vitamin D blood levels increased by 50% in the fourth quarter of 2009 compared to the previous year. In addition, sales of vitamin D supplements totaled $235 million in 2008 up from $43 million in 2001. (NYT Feb 2010) Clearly, this is an issue that is on everyone's mind.
As a gastroenterologist who sees patients at higher risk for colorectal cancer, I recommend calcium and vitamin D supplementation for prevention of colorectal polyps and cancer. This is especially important during winter months when vitamin D levels are lowest due to decreased sun exposure. African Americans, in particular, should discuss supplementation with their doctors because studies has shown that they might be at higher risk of vitamin D deficiency. Research, including genetic studies as part of my Cancer Research Foundation Young Investigator Award, is ongoing to elucidate the biology and clinical application of vitamin D supplementation in cancer prevention. There are currently 140 active studies in vitamin D and cancer registered with the National Institute of Health (clinicaltrials.gov). This wealth of research is truly our "best hope against cancer" especially cancer prevention.
Sonia S. Kupfer is a 2009 Cancer Research Foundation Young Investigator Awardee and is an Instructor in the Department of Medicine, Section of Gastroenterology, Hepatology and Nutrition, at the University of Chicago Medical Center. Read more about her project titled:"Vitamin D Metabolism Genes and Risk of Colorectal Cancer in African Americans" here.
"Thanks to the hard work, commitment, and compassion of scientists, researchers, and organizations like the Cancer Research Foundation, there is renewed hope for discovering better treatments and eventually a cure for cancer.
I commend all of you for your outstanding contributions to the field of cancer research. For five decades, your commitment to the crusade against cancer has given hope and comfort to people across the nation."
Former President of the United States
May 05, 1997