Healthy vitamin D levels associated with significant decrease in cancer risk among women
A recent pooled analysis of a randomized trial and prospective cohort study determined that women with vitamin D levels of at least 40 ng/ml were associated with > 65% reduced risk of developing cancer.
Cancer is highly prevalent, affecting approximately 40% of men and women in their lifetime. In 2012, a total of 14 million new cases of cancer were diagnosed worldwide with 8.2 million cancer-related deaths. This number continues to rise with an estimated increase of 22 million cancer cases within the next 20 years.
Cancer creates a significant financial burden. In 2010, cancer care accounted for a total of $125 billion in the U.S. alone. With cancer diagnoses continuing to grow, this number is projected to go up to $150 billion by 2020. Therefore, it is important for physicians to implement preventative measures in order to decrease the medical and financial burden of those affected by this disease.
Current evidence suggests that vitamin D status is inversely associated with several types of cancer, including prostate, lung and breast cancer. Furthermore, vitamin D has shown to exert anti-cancer properties. There are several mechanisms that may be responsible for these findings, including vitamin D’s ability to prevent cellular proliferation, promote programmed-cell death and decrease inflammation in cancer cells.
Although the role of vitamin D in cancer has been studied extensively, researchers recently aimed to determine if the previous findings are replicable, and to identify a reference range of 25(OH)D levels for the ideal prevention of cancer development among women 55 years and older.
In the current study, the researchers utilized data from two cohorts: The Lappe cohort (a double blind randomized control trial) and the GrassrootsHealth cohort (a prospective cohort). Unlike other studies, these studies represented different median vitamin D levels, offering a broader range of 25(OH)D concentrations to analyze.
The Lappe cohort took place in Nebraska, and evaluated a total of 1,169 women over the age of 55 years with no history of cancer. The participants were randomly assigned to one of the following treatments: calcium plus vitamin D placebo (either 1400 mg/day of calcium citrate or 1500 mg/day of calcium carbonate, calcium plus vitamin D (calcium as mentioned previously plus 1000 IU/day of vitamin D3), or control (calcium and vitamin D placebos).
The GrassrootsHealth cohort, conducted by a fellow public health non-profit in San Diego, CA, gathered the vitamin D levels of 1,135 women ages 55 and older who voluntarily joined the study with the aim to reach and sustain a serum 25(OH)D level of the participant’s choice. The participants measured their vitamin D levels via in-home vitamin D tests and reported their health outcomes by filling out an online questionnaire.
The researchers pooled data from both cohorts and compared the incidence of cancer with the subsequent vitamin D concentration over a median if 3.9 years. All types of cancers were included in the analysis, with the exception of non-melanoma skin cancer.
Did the researchers find a relationship between vitamin D status and cancer incidence in women? Here is what they found:
- The median baseline vitamin D status was 28 ng/ml in the Lappe cohort and 43 ng/ml in the GrassrootsHealth cohort (p<0.0001).
- There was a total of 840 cases of cancer per 100,000 individuals in the combined cohort (1,020/100,000 persons in Lappe cohort and 722/100,000 individuals in GrassrootsHealth cohort).
- Cancer incidence was lower for individuals with higher levels of vitamin D.
- At baseline, there was a 77% decreased incidence rate of cancer for those with levels > 40 ng/ml compared to those with < 20 ng/ml.
- The greatest decrease in cancer risk occurred between 10–40 ng/ml, with a further beneficial effect at levels ≥40 ng/ml.
- A 25(OH)D > 40 ng/ml was associated with a 67% decreased risk of cancer compared to those with a vitamin D status of < 20 ng/ml, after adjusting for several cofactors (age, BMI, smoking and calcium supplementation).
The researchers summarized their findings,
“We found a clear association between 25(OH)D serum concentration and cancer risk, according to multiple types of analyses. These results suggest the importance of vitamin D for the prevention of cancer.”
As always, it is important to note the limitations to this study. The use of self-reported data may result in recall bias, potentially skewing the results. Additionally, not all covariates could be accounted for. Furthermore, the analysis did not have the power to evaluate the role of vitamin D status on specific cancer types. Lastly, the study showed the relationship between vitamin D and cancer risk specifically among non-Hispanic, white women 55 years and older; therefore, the results may not be generalizable to other target populations.
The researchers concluded,
“Primary prevention of cancer, rather than solely expanding early detection or improving treatment, will be essential for reversing the current upward trend of cancer incidence worldwide; this analysis suggests that improving vitamin D status is a key prevention tool.”
Citation
Sturges, M. & Cannell, JJ. Healthy vitamin D levels associated with significant decrease in cancer risk among women. The Vitamin D Council Blog & Newsletter, 2016.
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