Circadian rhythm of some parameters of body composition in the elderly investigated by means of bioelectrical impedance analysis.

We studied the within-day determinations of some body composition (BC) parameters in clinically healthy elderly subjects with the aim of investigating their circadian rhythms (CR), which are known to vary in a circadian manner in clinically healthy young adults. The study involved six non-smoking, clinically healthy elderly males (mean age: 75 +/- 4 years; mean weight: 71.07 +/- 10.26 kg; mean height: 170 +/- 5 cm, mean BMI: 24 +/- 1 kg/m2). The BC parameters were determined by means of bioelectrical impedance analysis (BIA) at 2-hour intervals during the day and night, with the subjects lying horizontally in bed. The time-qualified BC estimates were analysed using the Cosinor method. The analysis revealed that the healthy elderly subjects had lost the CR of a number of the BC parameters, including fat body mass, cell body mass, extracellular body mass, total body water, extracellular body water, intracellular body water, and the Na and K exchangeable pools. However, they still retained the CR of body weight and lean body mass, with the expected nocturnal phase of oscillation. The abolition of the CR of the majority of BC parameters in the elderly suggests that human senescence is characterised by consistent changes in the daily rhythmic patterns of fat, water and electrolyte metabolism.