Premenopausal women who consume higher amounts of calcium and vitamin D may lower their risk of developing breast cancer by almost 40 per cent, new research suggests.
But post-menopausal women may not benefit from the vitamin and mineral combination said the researchers behind the new study from Brigham and Women's Hospital and Harvard Medical School.
"Findings from the present study suggest that higher intakes of calcium and vitamin D from dietary plus supplemental sources may be associated with a lower risk of breast cancer among premenopausal women," wrote lead author Jennifer Lin in the Archives of Internal Medicine. "The inverse association in premenopausal women may be more pronounced in more aggressive breast tumours."
Every year, ver one million women are diagnosed with breast cancer worldwide, with the highest incidences in the US and the Netherlands. China has the lowest incidence and mortality rate of the disease.
Lin and co-workers assessed 10,578 pre-menopausal and 20,909 post-menopausal women (average age 55.2, average BMI 25.9 kg per sq. m) using a questionnaire about their medical history and lifestyle, plus a 131-item food frequency questionnaire (FFQ) to detail food, beverage and supplement consumption during the previous year.
Over an average of 10 years of follow-up, the researchers documented 276 cases of breast cancer in pre-menopausal women and 743 cases in postmenopausal women. Among the pre-menopausal women, calcium and vitamin D intake were associated with a 39 and 35 per cent lower risk of breast cancer respectively, comparing the highest with the lowest intakes. No such benefits were observed in post-menopausal women.
"A possible explanation for the evident difference by menopause status may be related to the joint relationship among calcium, vitamin D and insulin-like growth factors (IGFs)," wrote the researchers.
"In vitro studies have suggested that calcium and vitamin D exert anticarcinogenic effects on breast cancer cells expressing high levels of IGF-1 and IGF binding protein 3. Calcium, vitamin D and IGF binding protein 3 have been shown in vitro to interact with each other in promoting growth inhibition in breast cancer cells," they added.
Since blood levels of these compounds decline with age, they would be more prevalent in younger, pre-menopausal women, they said.
The authors note several limitations with their study, including the measurement of nutrient intake only being taken at the start of the study, so changes in intake would not have been taken into account. Also, no information was obtained concerning sunlight exposure, which may drastically affect vitamin D levels.
"Further investigation is warranted to study the potential utility of calcium and vitamin D intake in reducing the risk of breast cancer," concluded the authors.
The results add to an ever-growing body of evidence linking vitamin D status with incidence and risk of various cancers, including breast, colorectal and prostate. Indeed, the link between vitamin D intake and protection from cancer is not and 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."
Source: Archives of Internal Medicine
Volume 167, Number 10, Pages 1050-1059
"Intakes of Calcium and Vitamin D and Breast Cancer Risk in Women"
Authors: J. Lin, J.E. Manson, I-M. Lee, N.R. Cook, J.E. Buring, S.M. Zhang