MedicalResearch.com Interview with:
Joan M. Lappe, Ph.D., R.N., F.A.A.N.
Associate Dean for Research, College of Nursing
Criss/Beirne Professor of Nursing
Professor of Medicine
Omaha NE 68131
MedicalResearch.com: What is the background for this study? What are the main findings?
- Numerous observational studies show that higher vitamin D intake and serum 25, hydroxyvitamin D [25(OH)D], the functional indicator of vitamin D status, are associated with lower incidence of cancer.
- However, the scientific fields consider randomized clinical trials (RCT) as a gold standard for testing new interventions for prevention and treatment of disease. In the only RCT of cancer and vitamin D to date with cancer as a primary outcome, the Women’s Health Initiative, postmenopausal women randomly assigned to vitamin D3400 IU/day and calcium 1000 mg/day showed no difference from those assigned to placebo in colorectal cancer incidence. One criticism of that study was that the vitamin D intervention was low, only 400 international units (IU) per day.
- In our study we found that, in healthy women ages 55 and older with a mean baseline serum 25(OH)D of 33 ng/mL, supplementation with 2000 IU/day of vitamin D3and 1500 mg/day of calcium for four years, compared with placebo, decreased all-type cancer incidence by about 30%, but this did not reach statistical significance. (p value =0.057 and for statistical significance, the p value would need to be less than 0.05.)
- In a secondary analysis, we re-analyzed the data excluding cancers that developed during the first year of study and were likely present but not diagnosed upon study enrollment. The findings here were that vitamin D and calcium did significantly decrease cancer risk by about 35%.
- In another secondary analyses, we combined all of the serum 25(OH)D values to determine if higher levels were associated with lower cancer incidence. Here, higher serum 25(OH)D was significantly associated with lower cancer incidence. Persons with serum 25(OH)D of 55 ng/mL had a 35% lower risk of cancer than persons with serum 25(OH)D of 30 ng/mL. This is especially interesting since current recommendations for sufficient serum 25(OH)D levels are 20 ng/mL (the National Academy of Medicine) and 30 ng/mL (the Endocrine Society).
- Note that serum 25(OH)D is a better predictor of cancer development than assigning persons to supplement groups. Serum 25(OH)D takes into account poor compliance of the active supplement group with taking supplements, personal use of supplements by the placebo group, dietary vitamin D intake, sunlight exposure, and the variation among persons in absorption and metabolism of the vitamin D supplement.
MedicalResearch.com: What should readers take away from your report?
- Vitamin D3and calcium supplementation likely decrease the risk of cancer; however this study does not provide definitive evidence within a randomized clinical trial.
- The women in our study had a high baseline level of serum 25(OH)D compared to recommended levels and compared to the US population. (33% of the population has levels below 20 ng/mL while 60% have levels below 30 ng/mL. In populations with lower serum 25(OH)D, supplementation would likely have a greater effect.
- Our study does suggest that higher levels of serum 25(OH)D are associated with lower cancer risk.
- Furthermore, levels of serum 25(OH)D needed for maximum cancer prevention effects may be higher than currently recommended levels of 25(OH)D. As indicated earlier, current recommendations for sufficiency are 20 ng/mL and 30 ng/mL.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: Future studies should give vitamin D supplements to target varying levels of 25(OH)D. It is not the dose of vitamin D given that is important for effects but rather the level of serum 25(OH)D achieved. We need to determine what optimal serum 25(OH)D levels are for decreasing risk of cancer.
MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.
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Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trialAm J Clin Nutr June 2007 85: 6 1586–1591Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.