American Journal of Clinical Nutrition, Vol. 87, No. 3, 792-793,
March 2008
© 2008 American Society for Nutrition
Calcium supplementation and cancer incidence
Mark J Bolland and
Ian R Reid
Department of Medicine
University of Auckland
Private Bag 92 019
Auckland
New Zealand
E-mail: m.bolland{at}auckland.ac.nz
Dear Sir:
Lappe et al (1) reported that daily supplementation with 1400–1500 mg Ca or 1400–1500 mg Ca and 1000 IU vitamin D reduced the risk of cancer in healthy postmenopausal women over 4 y by 47% and 60%, respectively. Previously, we reported the results of a 5-y randomized, placebo-controlled trial of daily supplementation with 1000 mg Ca or placebo in healthy postmenopausal women (2). The primary endpoint of our trial was fracture incidence, but a prespecified secondary endpoint was cancer incidence. In contrast with the findings of Lappe et al, we observed no effect of calcium supplementation on cancer incidence. As shown in Table 1
, 48 cancers occurred during the study in 46 of 732 women assigned to calcium supplementation compared with 43 cancers in 42 of 739 women assigned to placebo (P = 0.6).
The differences between our results and those of Lappe et al might have been due to the different doses or formulations of calcium used or to differences in some of the baseline characteristics of the groups. For example, the women in our study were older (mean age: 74 compared with 67 y), were lighter [mean body mass index (kg/m2): 26 compared with 29], had lower 25-hydroxyvitamin D concentrations (mean: 52 compared with 72 nmol/L), and had lower dietary calcium intakes (mean: 860 compared with 1150 mg/d). Additionally, in our study, there was no combined calcium and vitamin D supplementation group, but Lappe et al reported that the risk of cancer was lower in women with higher 25-hydroxyvitamin D concentrations at baseline, and the reduction in risk of cancer appeared to be greatest in women receiving combined calcium and vitamin D supplementation. Another possible explanation for the discrepant findings was the unexpectedly high rates of cancer in the placebo group of the study by Lappe et al. The annualized incidences of cancer in that group were 1.7% over the entire study and 2.3% over the last 3 y of the study. These values are substantially higher than the value that we observed in the placebo group of our study (1.2%) and higher than the annualized incidence (1.1%) in the placebo groups of the 2 hormone replacement arms of the Women's Health Initiative (3, 4), in which the participants had baseline characteristics similar to the participants in the study of Lappe et al. Thus, the findings of Lappe et al might have resulted, in part, because of an increased cancer incidence in the placebo group rather than because of a benefit of either calcium or calcium plus vitamin D supplementation.
ACKNOWLEDGMENTS
The authors had no conflicts of interest to declare.
REFERENCES
- Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr 2007;85:1586–91.[Abstract/Free Full Text]
- Reid IR, Mason B, Horne A, et al. Randomized controlled trial of calcium in healthy older women. Am J Med 2006;119:777–85.[Medline]
- Anderson GL, Limacher M, Assaf AR, et al. Effects of conjugated equine estrogen in postmenopausal women with hysterectomy: the Women's Health Initiative randomized controlled trial. JAMA 2004;291:1701–12.[Abstract/Free Full Text]
- Rossouw JE, Anderson GL, Prentice RL, et al. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women's Health Initiative randomized controlled trial. JAMA 2002;288:321–33.[Abstract/Free Full Text]
