To the Editor Dr Lappe and colleagues concluded that vitamin D and calcium supplementation compared with placebo did not reduce the risk of cancer in healthy older women.1 However, we believe their conclusion may be premature.
First, the 4-year length of follow-up may have been insufficient. Keum and Giovannucci2 reported that over 2 to 7 years the benefit of vitamin D supplementation may be limited to cancer mortality without much of an effect on cancer incidence.
Jaroudi S, Peiris A. Vitamin D Supplementation and Cancer Risk. JAMA. 2017;318(3):299. doi:10.1001/jama.2017.7833
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