The study, published in the British Medical Journal, is said to be the largest of its kind to date and adds to the science supporting the apparent health benefits from increased vitamin D. Indeed, a meta-analysis published in the American Journal of Preventive Medicine in 2007 reported that higher blood levels of vitamin D were associated with a lower risk of colon cancer.
The link between vitamin D intake and protection from cancer dates from the 1940s when Frank Apperly demonstrated a link between latitude and deaths from cancer, and suggested that sunlight gave "a relative cancer immunity".
“However, before any public health recommendations can be made for vitamin D supplementation, new randomised trials are needed to test the hypothesis that increases in circulating 25-(OH)D concentration are effective in reducing colorectal cancer risk without inducing serious adverse events,” wrote the researchers behind the new study, from six European countries.
Using data from over half a million participants of the European Prospective Investigation into Cancer Study (EPIC), the researchers analysed dietary and lifestyle information obtained from questionnaires, and collected blood samples.
During the course of the study, 1,248 cases of colorectal cancer were diagnosed and matched with 1,248 healthy controls.
Colorectal cancer accounts for nine per cent of new cancer cases every year worldwide. The highest incidence rates are in the developed world, while Asia and Africa have the lowest incidence rates.
It remains one of the most curable cancers if diagnosis is made early.
The EPIC data showed that blood levels of vitamin D below a mid-level of 50 to 75 nanomoles per litre were associated with an increased risk of colorectal cancer, while blood levels above this were not associated with any additional benefits, said the researchers.
The association was significantly stronger for colon cancer than rectal cancer, added the researchers.
“Additionally, higher consumption of dietary calcium, but not dietary vitamin D, was found to be associated with a reduced risk of colorectal cancer,” they report.
Commenting on the potential protective action of vitamin D with respect to colorectal carcinogenesis, the EPIC scientists noted that both vitamin and mineral may be involved. “The main proposed colorectal cancer protective mechanisms of calcium action (binding bile acids and fatty acids) could pertain largely to its concentration in the colorectal milieu rather than to a direct vitamin D-mediated effect,” they said.
The potential benefits for the vitamin, alone or in combination with calcium, for colorectal health are somewhat controversial, with some studies reporting benefits while others report null results.
Indeed, back in 2006 results from the Women's Health Initiative (WHI) stated that daily supplements of vitamin D and calcium 'had no effect' on the risk of colorectal cancer. The results were questioned however and independent cancer experts said at the time that the claims should be interpreted in the light of the complexities of the study.
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, with 69 per cent of the women enrolled on the Dietary Modification trial, 54 per cent enrolled on the Hormone Therapy trial, and 14 per cent enrolled on both.
"The enrolment in three overlapping trials maximised the participation and size of the WHI trial but created a complex approach with potential confounders for biological interpretation," said Forman and Levin.
Source: British Medical Journal
2010; 340: b5500, doi:10.1136/bmj.b5500
“Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations:a nested case-control study”
Authors: M. Jenab, H.B. Bueno-de-Mesquita, P. Ferrari, F.J.B. van Duijnhoven, et al.
Full-text available here.