Bioelectric and anthropometric assessments and reference data in the elderly.

Most studies using bioelectric impedance have estimated the volume of total body water, fat-free mass and on occasion extracellular fluid volume using whole-body resistance and reactance. However, the validity of bioelectric impedance has not been established for the elderly except in small samples of limited age ranges. The estimation of whole-body composition from impedance of body segments may be an alternative method that can be applied to many chair- and bedfast elderly patients. Also, measures of bioelectric impedance at lower and higher frequencies than 50 kHz are reported to differentiate the proportions of intra- and extracellular fluid volumes, and this could also provide important information about fluid quantities and balances in the elderly. Distribution statistics for body measurements for persons 65-85 y of age are available from the national health surveys and large clinical studies but reference data for persons > or = 80 y are sparse. Some reference data may be from groups that are not representative of the elderly because the samples were from cohorts older than elderly persons living today and significant group and racial differences existed among these as children and adults. These differences may have increased interindividual variances among the elderly. Suitable reference data for the present generations of elderly in the United States will be available with the culmination of NHANES III after 1994, but limited reference data for elderly persons up to 90 y of age have been published.(ABSTRACT TRUNCATED AT 250 WORDS)