Scientists from Emory University report that the potential benefits of the sunshine vitamin were even greater when people were also talking non-steroidal anti-inflammatory drugs (NSAIDs).
The results, published in the American Journal of Epidemiology, echo those of a large European study published earlier this year in the British Medical Journal, which was said to be the largest of its kind to date. Furthermore, 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".
The Emory scientists correlated blood levels of vitamin D3 - 25-hydroxyvitamin D3 (25(OH)D3) – against colorectal cancer risk in 616 people with colorectal cancer and 770 polyp-free controls.
After crunching the numbers, the researchers reported that: “Higher circulating 25(OH)D3 concentrations were statistically significantly associated with decreased colorectal adenoma risk”.
In people using NSAIDs, the potential risk reduction of higher vitamin D levels was increased to 66 per cent, added the researchers.
“These findings support the hypothesis that greater vitamin D exposure may reduce the risk of colorectal adenoma and suggest that it may do so more strongly in combination with anti-inflammatory agents,” concluded the scientists.
The potential benefits for the vitamin, alone or in combination with calcium, for colorectal health remain somewhat controversial, however, 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.
Data on D
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Source: American Journal of Epidemiology
Published online ahead of print, doi:10.1093/aje/kwq157
“Blood 25-Hydroxyvitamin D3 Concentrations and Incident Sporadic Colorectal Adenoma Risk: A Pooled Case-Control Study”
Authors: V. Fedirko, R.M. Bostick, M. Goodman, W.D. Flanders, M.D. Gross