Age-related decline in body cell mass in elderly men and women, determined by a noninvasive nuclear technique: effects of physical activity and dietary potassium intake.

The body cell mass (BCM) represents the actively metabolizing cellular components of the human body. In this study, the hypothesis was tested that physical activity and a sufficient dietary intake of potassium attenuate the age-related decline in BCM in the elderly. Cross-sectional data were collected in 82 male and 79 female non-institutionalized elderly (60-90 years) from Mainz, Germany, and were analyzed by age groups. BCM was calculated from total body potassium, measured by whole-body counting of naturally occurring 40K. Physical activity level (PAL) was assessed by a standardized questionnaire. Dietary intake of potassium (DIP) was estimated from a 7-day food diary. The results showed the following trends: (1) BCM decreased continuously from age 60 to 90 years by 11.2% (men) and 7.0% (women). BCM was inversely correlated with age in both sexes (men, P < 0.001; women, P < 0.05), but significant age group differences only existed for men (P < 0.01, one-way analysis-of-variance). Women had less BCM than men in all age groups (P < 0.001, t tests). (2) Correlation analyses demonstrated that in both sexes PAL declined with advancing age (P < 0.05), whereas DIP did not change significantly with age. (3) In both sexes, BCM showed a strong positive correlation with PAL (P < 0.001), but did not correlate significantly with DIP. Multiple linear regression analysis (independent variables were PAL, DIP, age, height, weight) demonstrated that PAL, age, and height explained 45% of the variability in BCM in men. In women, PAL was the only significant predictor of BCM, explaining 23% of the variance. The study supports the hypothesis that the level of physical activity is associated with the decline of BCM in the elderly.