Håkan Melhus, MD, PhD; Karl Michaëlsson, MD, PhD; Andreas Kindmark, MD, PhD
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Melhus H, Michaëlsson K, Kindmark A. Dietary Vitamin A Intake and Risk for Hip Fracture. Ann Intern Med. 1999;131:392. doi: 10.7326/0003-4819-131-5-199909070-00014
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Published: Ann Intern Med. 1999;131(5):392.
Dr. Sigurdsson would like clarification of the covariates that made the effect of retinol significant in the multivariate analysis in the bone mineral density study. He would also like to see the results after adjustment for vitamin D intake.
We tried to include the same set of covariates in both the hip fracture and bone mineral density studies (established osteoporosis risk factors). No major confounding was observed in the hip fracture study, but in the linear regression analysis of the bone density study, inclusion of possible confounders did change our estimates. Energy intake was the covariate with the most pronounced effect on the β estimates in the latter analysis. The bone density study included a more heterogeneous sample of women with regard to age and menopausal status. When we restricted the analysis of retinol intake to a dichotomous variable (> or < 1.5 mg/d), no major differences were seen between univariate and multivariate analysis (Table 5 of our article).
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