Design and data quality of a mixed longitudinal study to elucidate the role of dietary calcium and phosphorus on bone mineralization in pre-, peri-, and postmenopausal women

Abstract

The study design and data quality control of an ongoing study (10 yr duration) in a few hundred women are presented. Good variables with respect to their longitudinal usefulness are: body weight, body height, and span-width. Reasonable variables are the bone parameters of the radius (BMC, BW, and BMC/BW). Poor variables are: dietary calcium and phosphorus intake, dietary calcium-to-phosphorus ratio, urinary calcium-to-creatinine ratio, urinary sodium-to-creatimne ratio, hematocrit, serum alkaline phosphatase activity, serum γ-GT activity, and serum parathyroid-hormone concentration. Bad variables are: urinary phosphorus-to-creatinine ratio, urinary hydroxyproline-to-creatinine ratio, creatinine clearance, hemoglobin, MCHC, serum calcium, serum ionized calcium, serum phosphorus, serum total protein, serum albumin, and serum creatinine. In conclusion, it is possible to relate bone loss to food intake and to changes in anthropometric variables on an individual basis. However, quantification of the metabolic process is not possible.