Serum 25-hydroxyvitamin D concentrations greater than 40 ng/mL correlated with a 67% decrease in invasive cancer risk among women older than 55 years, according to an analysis of two study cohorts.
“We have quantitated the ability of adequate amounts of vitamin D to prevent all types of invasive cancer combined, which had been terra incognita until publication of this paper,” Cedric Garland, DrPH, adjunct professor in the department of family medicine and public health at UC San Diego School of Medicine and member of UC San Diego Moores Cancer Center, said in a press release. “These findings support an inverse association between serum 25-hydroxyvitamin D and risk of cancer.”
Increasing concentrations to a minimum of 40 ng/mL in the general population might substantially reduce cancer incidence and associated mortality, according to the researchers.
Although many epidemiologic studies have demonstrated an inverse association between levels of serum 25-hydroxyvitamin D, or serum 25(OH)D, and cancer risk, Garland and colleagues sought to quantify this association across a broader range of serum 25(OH)D levels. They sought to evaluate vitamin D levels and the risk for invasive, non-skin cancers in women older than 55 years.
Researchers pooled data from two different studies of non-Hispanic white women with different median 25(OH)D concentrations — the Lappe cohort (n = 1,169; median of within-subject mean 25(OH)D, 30 ng/mL) and the GrassrootsHealth cohort (n = 1,135; median of within-subject mean 25(OH)D, 48 ng/mL).
Women in the Lappe cohort were randomly assigned to receive calcium alone, calcium plus vitamin D or placebo. Women in the GrassrootsHealth cohort tracked and sustained a serum 25(OH)D concentration of their choice.
The median age of the total cohort (n = 2,304) was 64 years. The median baseline 25(OH)D was 34 ng/mL and the mean 25(OH)D — or the mean of all 25(OH)D measurements during the observation period — was 37 ng/mL. Median follow-up was 3.9 years.
Fifty-eight women in the combined cohort received an invasive, non-skin cancer diagnosis during the observation period. This translated into a combined cancer incidence rate of 840 per 100,000 person-years, or 1,020 cases per 100,000 person-years in the Lappe cohort and 722 cases per 100,000 person-years in the GrassrootsHealth cohort. Breast cancer was the most common cancer diagnosis in the total cohort (43% of all diagnoses).
Overall, higher concentrations of mean and baseline 25(OH)D concentrations correlated with significant decreases in cancer incidence.
Women with a baseline 25(OH)D of 40 ng/mL or greater demonstrated a 77% decrease in the incidence of cancer compared with women who had a baseline 25(OH)D less than 20 ng/mL. Further, a mean 25(OH)D concentration of 40 ng/mL or greater compared with less than 20 ng/mL corresponded with a 71% lower cancer incidence.
Results of a Cox multivariate regression analysis that adjusted for age, BMI, smoking status and calcium supplement intake showed women in the pooled cohort who had a 25(OH)D concentration of 40 ng/mL or greater demonstrated a 67% decrease in cancer risk compared with women with 25(OH)D concentrations less than 20 ng/mL.
Women with 20-ng/mL to 39-ng/mL 25(OH)D concentrations demonstrated a 43% decreased cancer risk compared with those whose concentration was less than 20 ng/mL.
Women who received 1,000 mg or more per day of calcium supplement demonstrated an insignificantly reduced cancer risk (hazard ratio = 0.81).
The researchers acknowledged limitations of the study which did not control for family history of cancer, diet, physical activity or alcohol, and relied on some self-reported data. The differences between the two cohorts, such as demographic characteristics and study methods, may also have impacted the results.
“Primary prevention of cancer, rather than solely expanding detection or improving treatment, will be essential for reversing the current upward trend of cancer incidence worldwide,” the researchers wrote. “This analysis suggests that improving vitamin D status is a key prevention tool.” – by Nick Andrews
McDonnell SL, et al. PLoS One. 2016;doi:10:1371/journal.pone.0152441.
Disclosure: Bio-Tech Pharmacal partially funded the study. The researchers report no relevant financial disclosures.