Background: Together with bone mass, muscularity and adiposity constitute the three major components of body composition. The latter two, independent of bone mass, influence largely the morbidity and mortality in old age. / The adverse effect of adiposity on morbidity and mortality in mid-life is well established but it remains intriguing in late-life. Whether adiposity is deleterious or is paradoxically protective for survival in older adults remains elusive. Body mass index (BMI) in mid-life has been used as a conventional measurement of adiposity and has been categorized to predict cardiovascular risk and mortality. Therefore the majority of the data was collected from early and mid-life adults. However, the predictive validity of these reference values in older adults is uncertain. / The second component in body composition is muscularity. Both muscle strength and muscle mass can affect morbidity and perhaps mortality as well. Age-associated muscle loss or sarcopenia adversely affects physical function and therefore the daily activities and the quality of life in old age. Very few studies of muscle loss have been undertaken in Asian and Chinese population. In addition, data about the longitudinal change in muscle mass, muscle strength and muscle function is lacking in older Chinese. / Physical function depends not only on muscle mass and strength but also on cognitive function which executes the motor task. Impaired cognitive function can give rise to derailed motor task execution despite good muscle strength. Physical limitations in cognitive decline may be secondary to sarcopenia, dys-execution of motor task, or both. On the other side, motor impairment can occur early in the process of neuro-degeneration. Whether it is the early manifestation of dementia rather than its sequel remains uncertain. / Muscle mass and strength is positively associated with BMI. In the lower end of BMI, underweight together with muscle loss will certainly result in physical limitations. In the upper end of BMI, however, the interaction between muscularity and adiposity is more complicated. Sarcopenic obesity is prevalent in the western populations but much less is known in Asian and Chinese population, not to mention in old age. BMI, though is protective against sarcopenia, will affect physical function adversely at its upper end. This paradox needs reconciliation. Perhaps an optimal ratio between adiposity and muscularity, representing the amount of adiposity supported by one unit of muscle mass can non-paradoxically be related to physical limitations. / Contraction in vertical dimension or height loss is a common occurrence in late life. Age-associated stature decline has been attributed to both clinical and subclinical vertebral fractures secondary to established osteoporosis. However its significance may extend beyond bone loss. Senile kyphosis can affect postural stability in locomotion and may result in falls and fractures independently of bone mass. The health impact of contraction in vertical dimension has less often been examined. / While the contraction in vertical body dimension may have health impact and significance, the risk of excess in horizontal dimension, waist circumference and waist-hip ratio have been well accepted and widely applied in the conventional cardiovascular mortality risk assessment. Whether central adiposity exerts similar adverse effect in old age or older adults are more resistive to the hazard of central adiposity remains unanswered. / Against this background, I together with my colleagues have conducted a series of studies to examine how body composition, adiposity and muscularity, and how body dimension, contraction in vertical dimension (height loss) and excess in horizontal dimension (central adiposity), affect the mortality, physical limitation and cognitive decline in old age. / Hypothesis: I hypothesize that (1) Adiposity in older adults is protective for survival (2) Muscularity alone and in combination of adiposity is related to physical limitation and cognitive decline (3) Excess in horizontal dimension (central adiposity) is adaptive and can be beneficial for survival while contraction in vertical dimension (height loss) is degenerative and deleterious to health / Methods: In collaboration with my colleagues, I have conducted a territory-wide prospective health survey in older adults. Four thousand community-dwelling men and women aged 65 years or over were recruited between August 2001 and December 2003. The sample was stratified so that approximately 33% were in each of the age groups: 65-69, 70-74 and 75 and over. / Muscle and fat mass, and their distribution, together with bone mineral density were examined using dual-energy X-ray absorptiometry (DXA) by a Hologic QDR 2000 densitometer (Hologic, Waltham, WA). Body weight and body dimensions: stature, waist and hip circumferences were recorded. Their grip strength was measured by hand grip dynamometer (Jamar Hand dynamometer 5030 J1, Sammons Preston, INC, Bolingbrook, IL, USA). Participants were asked to stand up with folded arms from a chair 5 times and the time required was recorded. The time to walk 6 meters at normal pace and the step lengths were measured. / A questionnaire containing information regarding demographics, physical activity level (PASE score), physical limitation and medical diagnosis was administered by trained interviewers. / Cognitive function was assessed by trained interviewers using the cognitive score of the Chinese version of the Community Screening Instrument of Dementia (CSI-D) and the Mini-mental Status Examination (MMSE) score. / The body composition measurements, body dimension (stature and waist hip circumferences) measurements, physical performance tests and cognitive function were repeated prospectively in the second year and 4th year visits. Mortality status was ascertained annually through the Hong Kong Special Administrative Region Death Registry. / Results: Adiposity -- We have observed a beneficial effect of adiposity for survival in older men. The crude mortality hazard ratio decreased consistently by 0.85 (p<0.005) and 0.86 (p<0.005) per every quintile increase in body mass index (BMI), and body fat index (BFI) respectively. The best survived men fell into a BMI range of 25, which is defined as overweight in the Asia-Pacific classification of BMI. Furthermore, the highest two quintiles of whole body fat percentage were associated with significantly lower all-cause mortality. Therefore older men were resistive to the hazard of being overweight and may benefit from being overweight and slightly obese. / Muscularity -- The mean relative appendicular skeletal mass (ASM/height square) was 7.19 and 6.05 kg/m2 in men and women respectively. / The relationship between muscle mass, muscle function and cognitive function is more complex and perhaps is bidirectional. In both older men and women, the cognitively impaired (CSI-D cognitive score ≦28.40) group had weaker grip strength (-5.10 kg, p =0.000 in men; -1.08 kg in women, p =0.000) and performed worse in the two physical function tests (in men, 6-meter walk speed, -0.13 m/s, p =0.000, chair stand test, 1.42 seconds, p =0.000; in women, 6-meter walk speed, -0.08 m/s, p = 0.000, chair stand test, 1.48 seconds, p =0.000) After adjustment for age, ASM, PASE and other co-morbidities, significant differences in grip strength (-2.60 kg, p =0.000 in men; -0.49 kg, p = 0.011 in women) and the two physical function tests persisted between the cognitively impaired and non-impaired group (in men, 6-meter walk speed, -0.072m/s, p = 0.001, chair stand test, 0.80 seconds, p = 0.045; in women, 6-meter walk speed, -0.049 m/s, p =0.000, chair stand test, 0.98 seconds, p =0.000). Therefore muscle loss though coexisting with cognitive decline, cannot fully account for the poorer physical function and weaker muscle strength observed in the cognitively impaired older adults. / In a reverse direction, I have also examined if loss in muscle mass and strength can precede cognitive decline. In men, being underweight, having a lower ASM, a weaker grip strength, a slower chair-stand test, a shorter step length and a slower timed walk were significantly associated with a lower MMSE score 4 years afterwards. In women, all except underweight and a lower ASM were significantly associated with MMSE score 4 years later. Therefore being underweight, having weaker grip strength, a slower chair-stand test, a shorter step-length in men and weaker grip strength in women, was associated with faster cognitive decline over a four year period. Weak grip strength is a predictor of faster cognitive decline in both genders. / Adiposity and Muscularity in combination -- Having analyzed adiposity and muscularity individually, I have combined the two and examined whether the adiposity to muscle ratio, as conceptualized as the weight of fat supported by one unit of muscle, can predict incident or worsening physical limitation. In men having BMI >23, all 3 adiposity to muscle ratios were predictive of physical limitation. (all p values <0.001) In women, throughout the entire BMI range, all 3 adiposity to muscle ratios were associated with physical limitation 4 years later both before and after adjustment. (all p values <0.05) Therefore sarcopenia and sarcopenic obesity as measured by either the body weight or fat mass bearing on a unit of muscle mass (the adiposity to muscle ratio), is a valid predictor of incident or worsening physical limitation in older women throughout the entire BMI range and in older men having BMI > 23. / Loss in vertical dimension (Height loss) -- I have conducted a prospective analysis about height loss in older adults across a period of four years. Twenty five (1.6%) men and 64 (4.0%) women lost >2 cm after 4 years. Rapid height loss (>2 cm after 4 years) was associated with excess all fractures and hip fractures (adjusted HR for all fractures = 2.86, p<0.001; adjusted HR for hip fractures = 4.74, p<0.01) in women but only hip fractures (adjusted HR = 4.93, p<0.05) in men. The all-cause (adjusted HR = 3.43, p<0.01) and respiratory disease mortality (adjusted HR = 5.64, p<0.05) were higher in men with rapid height loss while those in women were insignificant. Therefore modest height loss occurring in old age, >2 cm in 4 years, was associated with excess hip fracture, total and respiratory disease mortality in older men. In women, it was associated with excess BMD decline, all fractures and hip fractures but not mortality. Contraction in vertical dimension in late-life is hazardous to health. / Excess in horizontal dimension (Central adiposity) -- In answering whether central adiposity is hazardous or protective, we have examined the effect of the excess in horizontal dimension (central adiposity) by three measurements, namely waist-hip ratio (WHR), relative truncal fat (RTF), and relative abdominal fat (RAF). In men, the lowest mortality belonged to the quintile having WHR (0.92 – 0.94) and the second highest RTF quintile (mean WHR 0.94). In addition, the upper four quintiles of RAF (abdominal fat according to anatomical landmark in DXA / whole body fat) were associated with significantly lower all-cause mortality, and the adjusted hazard ratio (95% CI) in ascending quintiles of RAF compared with the lowest quintile was 0.62 (0.43–0.89), 0.58 (0.4– 0.85), 0.52 (0.36–0.77), and 0.67 (0.47–0.96). Therefore, in older men, excess in horizontal dimension or accumulation of central adiposity in late life may be beneficial for survival. / Conclusion: Body composition, as represented by adiposity and muscularity, is a major determinant of health in old age. In contrast to conventional belief, adiposity and being overweight may be beneficial for survival in late life. This may bear significant implication on the recommended cutoff values for BMI in the older population. Muscle loss can result in physical limitation and is related to cognitive impairment. In a reverse manner, loss in muscle mass and muscle strength can precede cognitive decline. When taking muscularity and adiposity together, the right balance between the two, or the adiposity to muscle ratio, is a predictor of physical limitation. When considering the two body dimensions, the vertical and the horizontal, loss in vertical dimension (height loss) in late life is hazardous for health while the excess in horizontal dimension (central adiposity) may be protective. Therefore the loss in vertical dimension is degenerative, and the excess in adiposity, both in general and in horizontal dimension, on the contrary, may be an ageing adaption to retain energy reserve for survival benefit rather than a degenerative process. / Au Yeung, Tung Wai. / Thesis M.D. Chinese University of Hong Kong 2015. / Includes bibliographical references (leaves 145-163). / Title from PDF title page (viewed on 14, September, 2016).
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_1291265 |
| Date | January 2015 |
| Contributors | Au Yeung, Tung Wai (author.), Chinese University of Hong Kong Graduate School. (degree granting institution.) |
| Source Sets | The Chinese University of Hong Kong |
| Language | English |
| Detected Language | English |
| Type | Text, bibliography, text |
| Format | electronic resource, electronic resource, remote, 1 online resource (xxii, 163 leaves, 62 variously numbered leaves) : illustrations (some color), computer, online resource |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons "Attribution-NonCommercial-NoDerivatives 4.0 International" License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
Page generated in 0.0045 seconds