Results from 2 studies suggest that vitamin D blood concentrations greater than 40ng/ml are linked to lower cancer risk
Thirty-five years ago, Garland and Garland hypothesized that vitamin D may have a protective effect against cancer when they noticed people living in higher latitudes were more likely to die of colon cancer. Today, many epidemiologic studies have supported this initial observation; in that, high blood serum levels of 25-hydroxyvitamin D [25(OH)D] (a marker for vitamin D) may be related to reduced cancer risk.
In a new study published in PLOS ONE, data from two cohorts were combined and analyzed; the Lappe cohort, a randomized clinical trial, and the GrassrootsHealth cohort, a prospective cohort. The analysis attempted to determine the relationship between vitamin D and the risk of cancer among non-Hispanic white women aged 55 years and older.
The Lappe cohort was a four year study examining the independent link of vitamin D and calcium supplements on cancer. Participants were given calcium, calcium plus vitamin D, or no supplements. Health status and supplement intake was assessed every 6 months.
The GrassroothsHealth Cohort required participants to submit to a home blood 25(OH)D test and complete an online health questionnaire every 6 months.
Overall, results showed that when vitamin D blood concentrations were higher, cancer incidence rates were lower and this association was prevalent with higher concentrations. Of note, women with vitamin D concentrations of 40 ng/ml or more were less likely to develop cancer. These findings suggest the importance of dosage on the protective effects of vitamin D. Calcium supplements did not appear to affect cancer risk.
Limitations of this study included the reliance of self-report data and the inability to control for other risk factors such as family history, diet, physical activity and alcohol use. There were also differences in methods between the 2 cohort studies in addition to issues regarding the generalizability of results to the overall population.
Nevertheless, these findings suggest that vitamin D concentrations greater than 40 ng/ml in the blood appear to reduce cancer risk, making vitamin D an important prevention tool against cancer.
Written By: Aurelie Hartawidjojo, BSc, BScPT