Total body water reference values and prediction equations for adults.

BACKGROUND: The clinical interpretation of total body water (TBW) necessitates the availability of timely comparative reference data. The prediction of TBW volume in renal disease is critical in order to prescribe and monitor the dose of dialysis in the determination of Kt/V. In clinical practice, urea distribution (V) is commonly predicted from anthropometric equations that are several decades old and for white patients only. This article presents new reference values and prediction equations for TBW from anthropometry for white and black adults. METHODS: The study sample included four data sets, two from Ohio and one each from New Mexico and New York, for a total of 604 white men, 128 black men, 772 white women, and 191 black women who were 18 to 90 years of age. The TBW concentration was measured by the deuterium or tritium oxide dilution method, and body composition was measured with a Lunar DXA machine. An all-possible-subsets of regression was used to predict TBW. The accuracy of the selected equations was confirmed by cross-validation. RESULTS: Blacks had larger TBW means than whites at all age groups. The 75th TBW percentile for whites approximated the TBW median for blacks at most ages. The white men and black men and women had the largest TBW means ever reported for healthy individuals. The race- and sex-specific TBW prediction equations included age, weight, and stature, with body mass index (BMI) substituted for weight in the white men. The root mean square errors (RMSEs) and standard errors for the individual (SEIs) ranged from approximately 3.8 to 5.0 L for the men and from 3.3 to 3.6 L for the women. In both men and women, high values of TBW were associated with high levels of total body fat (TBF) and fat-free mass (FFM). CONCLUSION: : TBW in these healthy adults is relatively stable through a large portion of adulthood. There are significant race and sex differences in TBW. These accurate and precise equations for TBW provide a useful tool for the clinical prediction of TBW in renal disease for white and black adults. These are the first TBW prediction equations that are specific for blacks.

Total body water data for white adults 18 to 64 years of age: the Fels Longitudinal Study.

BACKGROUND: Total body water (TBW) volume is reported to decrease with age, but much of the published data are 20 to almost 50 years old and are cross-sectional. Proper interpretation of clinical levels of TBW and trends with age necessitates the availability of current longitudinal data from healthy individuals. METHODS: Mixed longitudinal data for TBW of 274 white men and 292 white women (18 to 64 years of age) in the Fels Longitudinal Study were collected on a regular schedule over a recent eight-year period. The concentration of deuterium was measured by deuterium nuclear magnetic resonance spectroscopy. Body composition estimates were made with dual-energy x-ray absorptiometry, and random effect models were used to determine the patterns of change over time with and without covariates. RESULTS: The mean TBW data for the Fels men are either similar to or approximately 2 to as much as 6 liters greater than that reported by most other investigators 20 to 50 years ago. For Fels women, the mean TBW ranges from approximately 2 to as much as 5 liters less than that reported previously. These comparisons with much earlier studies reflect cohort effects and the secular changes in overall body size that have occurred during the past 60 to 70 years. These findings are reinforced by the fact that some early data sets included individuals born almost 140 years ago. After adjusting for the covariate effects of total body fat (TBF) and fat-free mass (FFM) with age, there were no significant age or age-squared effects on TBW in the men. In the women, after adjusting for the covariate associations of TBF and FFM with age, there was a small, but significant, negative linear association of TBW with age. In the men and women, the mean ratio of TBW to weight declined with age as a function of an increase in body fatness and more so for the men than the women. CONCLUSION: The findings from these mixed longitudinal data indicate that TBW volume, on average, maintains a reasonable degree of stability in men and women through a large portion of adulthood. These TBW data are recommended as current reference data for healthy adults.

Total-body and regional bone mineral content and areal bone mineral density in children aged 8-18 y: the Fels Longitudinal Study.

BACKGROUND: Techniques for cross-calibration of bone mineral content (BMC) and bone mineral density (BMD) between manufacturers of dual-energy X-ray absorptiometry (DXA) instruments are currently inadequate for total body measurements. Therefore, manufacturer-specific data for BMC and BMD in children are needed. OBJECTIVE: We provided age- and sex-specific means and SDs for total-body and regional BMC and areal BMD in 8-18-y-old white children. DESIGN: BMC and BMD of the head, arms, legs, pelvis, spine, and total body were determined by DXA. Data include 465 annual measurements from 148 healthy children with body weights between 30 and 100 kg and statures <190 cm. RESULTS: There were significant sex differences in BMC at ages 15-18 y for the total body and legs, at ages 12 and 15-18 y for arms and pelvis, at ages 11-13 and 16-18 y for the spine, and at ages 10-11 y for the head. There were significant sex differences in BMD at ages 16-18 y for total body, arms, and legs; at ages 12-13 and 16-18 y for the pelvis; at ages 12-14 and 18 y for the spine; and at ages 13-18 y for the head. CONCLUSIONS: Data presented in this investigation can be used to compare the BMC and BMD of 8-18-y-old white children (with statures <190 cm and body weights between 30 and 100 kg) using DXA.