by Craig Weatherby
During the 1940’s researcher Frank Apperly discovered that cancer death rates were lower in sunnier southern latitudes, and higher in northern climes.
Because sun exposure stimulates the body to make vitamin D, he hypothesized that this long overlooked hormone-like vitamin might provide cancer protection
Colorectal cancer accounts for almost 10 percent of new cancer cases every year worldwide. The highest rates are in the developed world, while Asia and Africa have the lowest rates.
At the time, Dr. Apperly suggested that sunlight conferred “…a relative cancer immunity.”
Controlled clinical trials would help prove him right.
But—combined with increased understanding of vitamin D’s physiological effects—virtually all of the large body of epidemiological evidence collected in recent years lends Dr. Apperley’s hypothesis strong support.
For example, evidence reviews published in 2006 and 2007 linked higher blood levels of vitamin D to reduced risk of colon cancer.
(See “Vitamin D and Calcium Boost Colorectal Health in New Trial,” “More Vitamin D = Less Breast and Colon Cancer,” and “Vitamin D May Drop Colon Cancer Risk Dramatically.”)
Now, the results of a substantial new study add urgency to calls for clinical trials regarding cancer, and to accelerate basic research into vitamin D’s many roles in the body.
Huge European study highlights vitamin D’s anti-cancer potential
The new population study is the largest study of its kind to examine the associations between vitamin D intakes and colon cancer rates (Jenab M et al 2010).
This was a “case-control” study, in which researchers compare the characteristics of people who develop a disease to those of an otherwise similar group of people.
The authors analyzed diet and health data and blood samples provided by participants in the European Prospective Investigation into Cancer Study (EPIC).
During the course of the study, 1,248 people were diagnosed with colorectal cancer, and the blood and diet data collected from those people was compared to the same data from 1,248 healthy people (i.e., “controls”).
Analysis links higher D levels to lower colon risk... up to a point
The European researchers grouped participants into five groups or “quintiles”, based on their vitamin D blood levels.
Their analysis showed that the people in the quintile with the highest vitamin D levels were 40 percent less likely to develop colorectal cancer over the course of the study, compared with those in the lowest vitamin D quintile
It also showed that, compared with people in the quintile with the highest blood levels of vitamin D, those with blood levels of vitamin D below a mid-level of 50 to 75 nmol/L (20 to 28 ng/mL) were 32 percent more likely to have colorectal cancer.
However, blood levels above this range were not associated with any additional drop in colon cancer risk.
As a Harvard team wrote in 2006, studies suggest that the most “advantageous” blood levels of vitamin D begin at 75 nmol/L (30 ng/mL), and that optimal levels are between 90 and 100 nmol/L (36-40 ng/mL) (Bischoff-Ferrari HA et al. 2006).
The Europeans also found no association between dietary vitamin D intake levels and colon cancer risk, possibly because people’s answers to diet surveys are rather unreliable—unless the number surveyed is much larger than this group—and because sun exposure plays a key role in determining vitamin D blood levels.
In addition, higher calcium intake was associated with a reduced risk of colorectal cancer.
The results of this large study indicate a strong inverse association between people’s blood vitamin D levels before a colon cancer diagnosis, and their risk of colorectal cancer.
As the authors wrote, “…randomized [clinical] trials are needed to assess whether increases in… [blood vitamin D levels]… can effectively decrease the risk of colorectal cancer” (Jenab M et al 2010).
Indeed, it’s way past time that the U.S. NIH and international agencies funded large clinical trials of dietary vitamin D to test its worth as an anti-cancer ally.
Findings further refute dubious results from Women's Health Initiative
The potential benefits of calcium and vitamin D supplements in relation to colorectal cancer came into question in 2006, when an analysis of data from the large Women's Health Initiative (WHI) study seemed to show that daily supplements of vitamin D and calcium had no preventive effect (Wactawski-Wende J et al. 2006).
However, those results were questioned by many cancer experts, who said that those findings should be taken with a big grain of salt in the light of the complexities of the study—which produced many “confounding factors” that muddied the waters badly—and the positive indications of most other studies.
For example, Michele Forman and Bernard Levin from the MD Anderson Cancer Center at the University of Texas noted that the WHI trial had three overlapping components, which as they wrote, “created a complex approach with potential confounders...” (Forman MR, Levin B 2006).
We will continue to follow this story!
- Bischoff-Ferrari HA, Giovannucci E, Willett WC, Dietrich T, Dawson-Hughes B. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr. 2006 Jul;84(1):18-28. Review. Erratum in: Am J Clin Nutr. 2006 Nov;84(5):1253. dosage error in abstract. Am J Clin Nutr. 2007 Sep;86(3):809.
- Forman MR, Levin B. Calcium plus vitamin D3 supplementation and colorectal cancer in women. N Engl J Med. 2006 Feb 16;354(7):752-4. Erratum in: N Engl J Med. 2006 Mar 9;354(10):1102.
- Holt PR, Bresalier RS, Ma CK, Liu KF, Lipkin M, Byrd JC, Yang K. Calcium plus vitamin D alters preneoplastic features of colorectal adenomas and rectal mucosa. Cancer. 2006 Jan 15;106(2):287-96.
- Jenab M et al. Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations: a nested case-control study. BMJ. 2010 Jan 21;340:b5500. doi: 10.1136/bmj.b5500.
- Wactawski-Wende J et al. Calcium plus vitamin D supplementation and the risk of colorectal cancer. N Engl J Med. 2006 Feb 16;354(7):684-96. Erratum in: N Engl J Med. 2006 Mar 9;354(10):1102.