The potential protective effects of the vitamin were not limited by the hormone receptor status of the tumours, according to research published online in the American Journal of Epidemiology.
“This study suggests that vitamin D is associated with a reduced risk of breast cancer regardless of [oestrogen-receptor (ER) positive and progesterone-receptor (PR)] status of the tumour,” wrote lead author Kristina Blackmore from Mount Sinai Hospital in Toronto.
Over one million women worldwide are diagnosed with breast cancer every year, with the highest incidences in the US and the Netherlands. China has the lowest incidence and mortality rate of the disease.
Hormone-sensitive oestrogen-receptor (ER) positive and progesterone-receptor (PR) positive tumours are said to be the most common type diagnosed among breast cancer patients in the US. These tumours are stimulated to grow by the female hormones oestrogen and progesterone.
“Few epidemiologic studies have considered the association between vitamin D and hormone-receptor-defined breast cancer,” wrote Blackmore.
In order to start filling this knowledge gap, the Canadian researchers analysed the vitamin D intakes of 759 women with breast cancer, and compared this to the vitamin D intakes of 1,135 healthy controls.
Increased intakes of the vitamin were associated with a 24 per cent reduction in the risk of developing ER+ and PR+ tumours, said the researchers. Moreover, increased intakes were also associated with 26 and 21 per cent reductions in the risk of receptor-negative (ER–/PR–) and mixed receptor (ER+/PR–) tumours. However, these last two associations were not significant, said the researchers.
“Future studies with a larger number of receptor-negative and mixed tumours are required,” they concluded.
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".
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. 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.
Source: American Journal of EpidemiologyPublished online ahead of print, doi:10.1093/aje/kwn198 “Vitamin D From Dietary Intake and Sunlight Exposure and the Risk of Hormone-Receptor-Defined Breast Cancer”Authors: K.M. Blackmore, M. Lesosky, H. Barnett, J.M. Raboud, R. Vieth, J.A. Knight