The new meta-analysis, published in the European Journal of Cancer, reports ‘ambiguous’ evidence for the beneficial effects of vitamin D in breast cancer – stating that whilst studies measuring vitamin D levels post diagnosis offer an inverse relationship, larger population studies must now confirm such results.
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 new study reviewed and summarised ten trials investigating the association between serum vitamin D (measured as 25(OH)D levels) and the risk of breast cancer.
Protective role
The review and meta-analysis summarising results on the association between serum 25(OH)D and incident breast cancer was reported to “show ambiguous evidence”.
Studies measuring serum 25(OH)D levels post diagnosis supported the theory that serum 25(OH)D levels are inversely associated with breast cancer risk, reported the authors. However the researchers noted that “a statistically significant inverse association remained unconfirmed”.
Our review and meta-analysis provide the most comprehensive and updated summary of epidemiological evidence to date on the association between serum 25(OH)D and BC risk," reported the authors.
In study concludes that whilst studies measuring 25(OH)D after diagnosis suggest an inverse association - a statistically significant relationship remained unconfirmed.
The researchers called for further long term population studies “to clarify the potential role and the relevant exposure time regarding vitamin D and breast cancer risk.”
“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,” stated the researchers.
Source: European Journal of Cancer
Published online ahead of print, doi: 10.1016/j.ejca.2010.03.037
“Meta-analysis: Serum vitamin D and breast cancer risk”
Authors: L. Yin, N. Grandi, E. Raum, U. Haug, V. Arndt, H. Brenner