Numerous studies have linked vitamin D levels to a reduction in the risk of certain cancers, including breast cancer, but much debate has focused on the means to boost vitamin D levels – supplements or sunlight.
According to new findings published in Cancer Epidemiology, Biomarkers & Prevention, a combination may be the best approach. Data collected over a decade of study from 67,721 women indicated that postmenopausal women living in sunny climes combined with high dietary or supplemental intakes of vitamin D were at a significantly reduced risk of breast cancer compared to women with high sun exposure and low intakes of the vitamin.
On the other hand, no associations were observed for dietary and supplemental intakes of vitamin D alone, report researchers led by Pierre Engel from Inserm (Institut National de la Santé et de la Recherche Médicale).
“Although, our results do not support a linear dose-response relationship of both UVR dose and dietary vitamin D on BC risk, our findings suggest that a threshold of vitamin D exposure is required to prevent BC; this minimal amount is likely to vary with individual ability to metabolize or synthesize vitamin D from both sources,” they said.
D and the big C
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".
Since then there have been numerous studies suggesting associations between vitamin D and lower risks of certain cancers.
Vitamin D refers to two biologically inactive precursors – cholecalciferol (D3) and ergocalciferol (D2).
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.
There is growing evidence that 1,25(OH)2D has anticancer effects, but the discovery that non-kidney cells can also hydroxylate 25(OH)D had profound implications, implying that higher 25(OH)D levels could protect against cancer in the local sites.
The association between vitamin D and breast cancer is still ambiguous, however, according to results of a recent meta-analysis published in the European Journal of Cancer (doi: 10.1016/j.ejca.2010.03.037).
According to findings of Dr Engel and his team, such ambiguity may be related to a combination of dietary, supplemental and sunlight exposure as the source of raising vitamin D levels.
The French researchers documented 2,871 cases of breast cancer over the 10 years of their study. While no relationship was observed between dietary and supplemental intakes of the sunshine vitamin, the risk of breast cancer for women residing in regions with the highest average daily UV exposure (living below a latitude of 46°N) combined with high dietary vitamin D intakes was 32 percent lower, while the risk for high UV exposure and high supplemental intakes was reduced by 45 percent.
“Considering that, in France, mean vitamin D dietary intake is low, and 25(OH) vitamin D serum concentrations are mostly below the 30 ng/mL recommended threshold, our results suggest that an increase in overall vitamin D intake should be encouraged by food and health agencies, possibly through fortification of foods,” concluded Dr Engel and his co-workers.
Jury–in or out?
The recent meta-analysis, which reviewed and summarised ten trials investigating the association between serum vitamin D (measured as 25(OH)D levels) and the risk of breast cancer, concluded that the data to date “show ambiguous evidence”.
“Data is still sparse and in depth analyses … especially measuring repeatedly 25(OH)D at different time points before diagnosis, are highly desirable to enable more precise estimates and a better understanding of the role of vitamin D in breast cancer development and prevention,” concluded the authors of the meta-analysis.
Source: Cancer Epidemiology, Biomarkers & Prevention
Published online ahead of print, doi:10.1158/1055-9965.EPI-10-1039
“Joint effects of dietary vitamin D and sun exposure on breast cancer risk: results from the French E3N cohort”
Authors: P. Engel, G. Fagherazzi, S. Mesrine, M-C. Boutron-Ruault, F. Clavel-Chapelon