Niha Zubair, Arivale Clinical Research Scientist, PhD
Earlier detection and better treatments have reduced the mortality rate of breast cancer. Unfortunately, there has been no similar reduction in the number of new breast cancer cases over the past two decades.
Past studies have suggested that higher concentrations of 25-hydroxyvitamin D – a major vitamin D biomarker – in a person’s body can lower their risk of breast cancer. However, many of those studies were unable to assess this association in concentrations of 25-hydroxyvitamin D, or 25(OH)D, over 40 ng/ml.
A 25(OH)D concentration of 20 ng/ml or more is generally considered adequate for bone and overall health. But, many people barely meet this criteria or are below it, making it difficult to assess how relatively higher concentrations of 25(OH)D affect or don’t affect breast cancer risk.
Unlike in previous studies, this new study was able to investigate the relationship between 25(OH)D and breast cancer risk across a broad range of concentrations in women 55 or older. Researchers pooled data from two randomized clinical trials and a prospective cohort study to obtain a larger population to analyze.
After pooling data, over 5,000 participants were included. Women were followed for a median of four years, during which time 77 were diagnosed with breast cancer.
The researchers grouped women based on their 25(OH)D concentrations and found an 82-percent lower incidence rate of breast cancer in women with concentrations of 60 ng/ml or more compared to women with concentrations under 20 ng/ml.
In addition, they found the highest proportion of breast cancer-free participants was in the 60 ng/ml or more group (99.3 percent) and the lowest proportion of breast cancer-free participants was in the under 20 ng/ml group (96.8 percent).
Statistical analysis revealed there was a continuing decrease in breast cancer risk for women with 25(OH)D concentrations between 20 and 39 ng/ml, 40 and 59 ng/ml, and 60 ng/ml or more in comparison to women with concentrations under 20 ng/ml.
Concentrations of 60 ng/ml or more seemed to be the most protective against breast cancer. Those women had an 80-percent lower risk of breast cancer than women with concentrations under 20 ng/ml. These results were observed after accounting for factors that could potentially influence 25(OH)D concentrations and breast cancer risk, such as age, BMI, smoking status, and calcium supplement intake.
Researchers concluded findings from this study suggest breast cancer incidence could be substantially reduced by increasing 25(OH)D concentrations well above 20 ng/ml, the current baseline recommendation for adequacy.
Emerging research suggests that vitamin D concentrations higher than 20 ng/ml are protective against some negative health outcomes. However, there are limitations to this current study.
First, the analysis only included women 55 or older, so the results may not apply to a younger population or men. In addition, the vast majority of participants were white/Caucasian, so the results may not be generalizable to persons of other ethnicities.
Next, because this was a pooled analysis of three individual studies, differences in population demographics and methods among the studies may have affected the results.
Additional limitations include the use of some self-reported data and not being able to account for some risk factors (family history of breast cancer, diet, and estrogen use).
As it stands, more research is needed to clearly determine what concentrations of vitamin D are optimal. As more evidence appears, public health organizations will hopefully alter vitamin D recommendations to encompass a more wide-range of health conditions.
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[Arivale Hot Topics address health stories currently in the news. The Arivale Clinical Team’s commentary on these news articles is not a review of the scientific evidence, nor an endorsement of a specific study, and is not meant as official medical opinion.]