Evaluation of the decline in total body potassium with age - Body Composition

Nutrition Research Newsletter, August, 2003

Total body potassium (TBK) is a measure of the body's cell mass and can be quantifiable by the detection of gamma-rays that emanate from the body by virtue of its content of the naturally occurring radioisotope of potassium ([sup.40.K]). It has been estimated that 60% of the body's potassium is found in skeletal muscle, and the rest in other organs and tissues. TBK can be used as an index of skeletal muscle mass and can provide an estimate of fat-free mass. Throughout adulthood, skeletal structures including muscle and bone are dynamically changing and influence cognitive and physical functional status, nutritional and endocrine status, quality of life, and comorbidity. Therefore, information regarding changes in TBK during the lifespan may be beneficial in identifying periods of high health risks in the primary care selling, with potential for treatment and prevention.

The aims of a recent investigation were to 1) investigate race-ethnic and sex differences in changes in TBK during adulthood and 2) identify age cutoffs when TBK values begin to decline in a cohort of African American, Asian, Hispanic, and White women and men. The subjects included 1368 women (299 African American, 197 Asian, 669 White, and 203 Hispanic) and 973 men (198 African American, 152 Asian, 44 White, and 179 Hispanic). Longitudinal data were available for 166 women and 88 men; the remaining subjects (89%) were measured once. Both cross-sectional and longitudinal data were used in the analysis.

Each subject completed a medical examination that included screening blood tests. Body weight and height were measured. The 4-pi whole body counter was used to measure [sup.40.K]. TBK was calculated from measured [sup.40.K].

The ages 30 and 31 were identified for women and men, respectively, as the cutoffs after which TBK began to decline. Both sexes had similar racial-ethnic patterns for expected mean TBK at the age cutoffs: African Americans had the highest value, followed by whites, Hispanics, and Asians. After the age cutoffs, the reduction in TBK differed by race and sex. In women, African Americans showed the most rapid decline, whereas Asians had the lowest. In men, Hispanics had the most rapid decline in TBK, followed by African Americans, whites, and Asians.

The results suggest significant sex and racial differences in the rate of change in TBK with age. Additional research is needed to investigate further the associations of declining TBK with potential health complications.

Q. He, M. Heo. S. Heshka, et al. Total body potassium differs by sex and race across the adult age span. Am J Clin Nutr; 78:72-77 (July, 2003). [Correspondence: D. Gallagher; Obesity Research Center, 1090 Amsterdam Avenue, 14th Floor, New York, NY 10025. E-mail: dg108@columbia.edu].