American Journal of Epidemiology Advance Access originally published online on July 21, 2006
American Journal of Epidemiology 2006 164(5):449-458; doi:10.1093/aje/kwj246
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Original Contribution |
Dairy, Magnesium, and Calcium Intake in Relation to Insulin Sensitivity: Approaches to Modeling a Dose-dependent Association
1 Center for Research in Nutrition and Health Disparities, Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, SC
2 Department of Epidemiology and Biostatistics, Arnold School of Public Health, University of South Carolina, Columbia, SC
3 Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC
Correspondence to Bo Ma, Center for Research in Nutrition and Health Disparities, Arnold School of Public Health, University of South Carolina, 2718 Middleburg Drive, Columbia, SC 29204 (e-mail: mab{at}mailbox.sc.edu).
Dairy intake has been inversely associated with insulin resistance, which may be partly due to the specific effects of calcium and magnesium. Data from the Insulin Resistance Atherosclerosis Study (1992–1999) for 1,036 US adults without diabetes at baseline were examined to evaluate the cross-sectional association of habitual dairy, magnesium, and calcium intake with insulin sensitivity at baseline and after 5 years of follow-up. Insulin sensitivity was directly measured with a validated, 12-sample, insulin-enhanced, intravenous glucose tolerance test with minimal model analysis. Dietary intake was assessed by a validated food frequency interview, and dietary supplement dose was confirmed by reviewing the supplement label. Several statistical approaches were used to ensure appropriate modeling of the dose-dependent association. No association was found between dairy intake and insulin sensitivity (p = 0.41); however, associations were positive for magnesium and calcium intake (p = 0.016) after adjusting for demographic, nondietary lifestyle and dietary factors, and food groups. Furthermore, magnesium intake was associated with insulin sensitivity in a threshold fashion, with a Bayesian method–estimated threshold (325 mg) (ß = 0.0607/100 mg, p = 0.0008 for <325 mg of magnesium/day; and ß = –0.001/100 mg, p = 0.82 for 
325 mg of magnesium/day). This study suggests that magnesium and calcium intake specifically, but not dairy intake, is associated with insulin sensitivity.
calcium; dairy products; insulin resistance; magnesium
Abbreviations: AIC, Akaike's Information Criterion; BIC, Schwarz's Bayesian Information Criterion; IRAS, Insulin Resistance Atherosclerosis Study; SI, insulin sensitivity index