Physical Activity, Sedentary Behaviour and Retinal Microvasculature

Satyamurthy Anuradha (2011). Physical Activity, Sedentary Behaviour and Retinal Microvasculature PhD Thesis, School of Population Health, The University of Queensland.

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Author Satyamurthy Anuradha
Thesis Title Physical Activity, Sedentary Behaviour and Retinal Microvasculature
School, Centre or Institute School of Population Health
Institution The University of Queensland
Publication date 2011-12
Thesis type PhD Thesis
Total pages 202
Total colour pages 11
Total black and white pages 191
Language eng
Subjects 111706 Epidemiology
111301 Ophthalmology
111799 Public Health and Health Services not elsewhere classified
1106 Human Movement and Sports Science
Abstract/Summary Background The eye is a unique site where the retinal microvasculature can be seen and examined in a non-invasive fashion through retinal imaging. Abnormalities in the retinal microvascular calibres (both arteriolar and venular) as well as other retinal microvascular signs (arteriovenous nicking [AV nicking], focal arteriolar narrowing and retinopathy) have been shown to provide insights into the cumulative microcirculatory  effects  of  an  individual’s  exposure  to  systemic  and  lifestyle  factors. Physical inactivity is an established risk factor for cardio-metabolic health, and the potential impact of sedentary behaviour (too much sitting) on health outcomes is being increasingly recognized. However, the associations of physical inactivity and sedentary behaviour with the retinal microvasculature remain largely unknown. Aims This thesis examines the associations of physical inactivity and time spent in sedentary behaviours with the retinal microvasculature among adults in large, population-based studies; and, explores gender and racial/ethnic differences between population sub-groups in these associations. Methods and Results The empirical evidence for this thesis was largely derived from cross-sectional, large-scale population- based studies conducted in different parts of the world (Australia, USA, Asia). In these studies, the retinal microvasculature was assessed using retinal microvascular calibre (measured quantitatively) and/or retinal microvascular signs (graded qualitatively). Most of the studies used self-reported behavioural measures of leisure-time physical activity and television (TV) viewing time (a commonly assessed, and highly prevalent sedentary behaviour) as the exposure measures. However, there was the opportunity within one study to investigate the associations using objectively-derived (accelerometer) measures of physical activity and sedentary time. To complement this research, and to understand some of the nuances of objective measurement of sedentary time, a field based study was conducted to provide accelerometry-based cut-points for the classification of sitting. Evidence from Australia This study used data from 2,024 adults of a predominantly Caucasian origin, who participated in the baseline Australian Diabetes, Obesity and Lifestyle (AusDiab) study (1999-2000). While no statistically significant association emerged for physical activity, more TV viewing among men was associated with a significantly wider venular calibre relative to lower amounts of TV viewing. This study provided the first evidence of adverse associations of TV viewing time with the microvasculature, thereby paving the way for further investigations in larger and more-varied population samples. Evidence from the USA A multi-ethnic population sample of nearly 6,000 adult participants from the USA (comprising whites, blacks, Hispanics and Chinese) were examined in the Multi-Ethnic Study of Atherosclerosis, MESA (2002-2004). Racial/ethnic differences were noted for the first time in this study in that those in the lowest quartile of leisure-time physical activity (among whites and Hispanics) had wider retinal venular calibres, compared to those in the highest quartile. Those in the highest quartile of TV viewing time (among whites) had wider venular calibres compared to those in the lowest quartile. Additionally, findings from the Atherosclerosis Risk-In-Communities (ARIC) study from the USA confirmed greater levels of sport-related physical activity to be beneficially associated with retinal microvascular signs among adults compared to lower amounts of physical activity. Finally, data from the National Health and Nutrition Examination Survey, NHANES (2005-06) provided the opportunity to explore associations of ActiGraph-derived measures of physical activity and sedentary time with retinal microvascular signs among 1,701 adults. Those in the lower two quartiles of physical activity had a significantly greater odds of AV nicking and focal arteriolar narrowing, compared to those in the highest quartile. Those with prolonged sedentary time had greater odds of AV nicking compared to those with the lowest sedentary time. Evidence from Asia The Singapore Prospective Study (2004-2007) allowed the examination of 3,866 Asian adults of Chinese, Indian and Malay origin. Lower levels of physical activity were associated with wider retinal venular calibre compared to the highest level. Greater TV viewing time (among women) showed detrimental associations with narrower retinal microvascular calibre when compared to those with the least TV viewing time. Furthermore, differences in associations were noted by ethnicity in that the associations of lower levels of physical activity were significant only among the Chinese, but not the other ethnic groups. Conclusions This thesis has shown adverse associations of lower levels of physical activity and higher levels of sedentary time with the retinal microvasculature in different populations across the globe. It has provided new insights into evidence relating these behavioural risk factors with cardiometabolic health outcomes by highlighting the contribution of early, subclinical small-vessel disease processes. Although significant racial/ethnic differences have been noted in the MESA and Singaporean studies, the minority racial/ethnic groups within the populations studied could have been underpowered to detect significant associations, even if true differences existed. Differences noted in these associations between gender and racial/ethnic groups should help to improve the understanding of health differences between population subgroups. Future prospective studies and intervention trials are needed to explore how changes in physical activity and sedentary behaviour will impact on the retinal microvascular characteristics.
Keyword physical activity
sedentary behaviour
television viewing
narrower arterioles
wider venules
arteriovenous nicking
Additional Notes Colour pages: 2,5,6,46,47,48,69,172,176,177,178 Landscape pages: 16, 17, 34, 61, 62, 89, 90, 100, 127, 128

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Created: Mon, 18 Jun 2012, 22:04:46 EST by Satyamurthy Anuradha on behalf of Library - Information Access Service