Age‐related decrease in energy expenditure at rest parallels reductions in mass of internal organs

Abstract

This study explores to what extent the mass of internal organs may impact the age-related decrease in energy expenditure at rest (EErest). The relationship between direct measurements of EErest in elderly women and predicted EErest based on equations deriving from the metabolic activity in tissue from younger women were also elucidated. Body composition of elderly women was measured by an impedance method. EErest was measured by the Douglas bag method after an overnight fast. These data were compared with predicted values of EErest based on equations derived from studies in younger women. The mass of internal organs was obtained from autopsy material. Young women (mean age 31.7 years, range 14-60, n = 104) and elderly women of 65 years (n = 22), 75 years (n = 26), and 85 years (n = 31) participated in this study. Autopsy data were obtained from women (n = 238) from the same birth cohorts as the elderly women who died at ages 42-87 years. EErest showed a progressive age-related decline, which appeared to parallel a similar reduction in the mass of internal organs derived from autopsy material of women who died at the same ages. In contrast, FFM was identical in the group of 65 and 75-year-old women, but was lower in the 85-year-old women. Predicted and measured EErest revealed a strong correlation in elderly women. Modest reductions in the mass of internal organs with a high metabolic rate appear to contribute markedly to the decline in EErest observed in aging. Further, it is also possible to predict EErest from the body composition of elderly women using equations developed from younger women.

Repository Describing an Aging Population to Inform Physiologically Based Pharmacokinetic Models Considering Anatomical, Physiological, and Biological Age-Dependent Changes

“…Liver is the major organ of metabolism. Liver weight was analyzed from over 3,000 subjects [29,41,51,52,55,69,72,78,87,88] and was found to be on average 1.78 kg in men and 1.49 kg in women with a CV of 23.7% till the age of 65 years. Thereafter, liver weight decreased by 10 to 15% in women per age decade reaching 1.03 kg at the age of 100 years.…”

“…The literature search yielded nine different studies with a total of 1,620 data points measuring kidney weight after autopsy [29,41,42,51,52,55,69,78,85] ( Figure 4A). The average kidney weight in young males and females was 0.318 kg with a CV of 19.3% and 0.259 kg with a CV of 23.2%, respectively.…”

“…Brain weight was analyzed by using data from eight different studies with 2,425 participants [29,41,42,51,52,55,78,139] and was found to be independent of age. The average brain weight was 1.39 kg in males and 1.28 kg in females with a gender-independent CV of 9%.…”

Advances in the Science and Application of Body Composition Measurement

“…Elucidating the extent of organ and tissue atrophy has important implications for understanding REE changes with age and REE‐related diseases such as obesity 54 , 55 . Autopsy data have shown a linear decline in organ weight with increasing age for the brain, liver, and kidneys, whereas weight for the heart increased with age 56 .…”

“…Elucidating the extent of organ and tissue atrophy has important implications for understanding REE changes with age and REE-related diseases such as obesity. 54,55 Autopsy data have shown a linear decline in organ weight with increasing age for the brain, liver, and kidneys, whereas weight for the heart increased with age. 56 We confirmed these findings in healthy African American and white adults (aged 19-88 years) using in vivo MRIderived organ measures (ie, older people have a smaller mass of brain, kidneys, liver, and spleen but not the heart compared to younger subjects).…”