Letter re: Calcium supplementation and risk of dementia in women with cerebrovascular disease.

Abstract

Kern et al.1 conducted a small, observational, retrospective, longitudinal, population-based cohort study of calcium supplementation and increased dementia risk in elderly women. Women who took calcium supplementation had higher odds of dementia. However, the number of individuals taking calcium supplements without vitamin D was low and compromised the reliability of the results. The sample size (n = 98) in the calcium supplements group included women taking calcium supplements with 85.7% (84 of 98) also taking vitamin D.1 The authors, recognizing vitamin D as a confounding variable, included it in regression models and stated that vitamin D did not affect the “main results.”1 However, controlling for vitamin D would not improve statistical power. Women taking calcium supplements with vitamin D should have been excluded at baseline because the dependent variable in the hypothesis was calcium supplementation alone.1 The calcium supplement group was described as “women treated with calcium supplements,”1 but they were actually women treated with calcium supplements, most of whom took vitamin D. Thus, the study hypothesis of calcium supplementation association with an increased risk of dementia was tested with a small sample size of 98 where only 14 individuals were relevant to the research question.