Longitudinal study of total body potassium in healthy men.

OBJECTIVES

Total body potassium (TBK) is an index of fat-free mass and an accurate measure of body cell mass (BCM). To date, however, no longitudinal studies have evaluated body composition using TBK in aging healthy adults. The purpose of this study was to assess TBK and BCM in healthy men over a 21-year period, and to evaluate changes with age.

DESIGN

A 21-year longitudinal, prospective, observational study evaluating TBK and BCM and their relationship to changes with aging and body mass index (BMI).

SUBJECTS

Body composition of 133 healthy Italian men, 20 to 66 years of age, was measured by whole-body counting of (40)K. TBK was calculated by using this formula: (40)K × 8.474. BCM was calculated from TBK by using this formula: BCM (kg) = 0.00833 × TBK (mmol).

RESULTS

The prevalence of overweight and obesity increased significantly from baseline to end of study (p < 0.01), with no change in TBK observed over the 21-year period. BCM summaries were tested to determine if any was a good predictor of BMI after age 30. Participants with a low maximum BCM (<27 kg) at an early age tended to exhibit decreased BMI as they aged, whereas those with a high maximum BCM (>27 kg) at an early age tended to show increased BMI as they aged.

CONCLUSION

Despite an overall increase in the incidence of overweight and obesity over the 21-year period, a high maximum BCM at an early age was a predictor of an increase in BMI as men got older.