Among adults, excessive sedentary behaviour (as characterised by those activities that involve sitting, in particular screen (TV or computer) viewing) is linked to increased risk for cardiovascular events,(1,2) all-cause mortality,(1) obesity,(3,4) dyslipidemia,(5) higher plasma glucose levels,(6) and the metabolic syndrome.(7) These links seem to be independent of participation in moderate-to-vigorous physical activity (MVPA). For example, among adults who meet the MVPA guidelines, significant, detrimental dose-response associations of sedentary time exist with all-cause and cardiovascular mortality,(1) waist circumference and BMI,(3) systolic blood pressure, 2-hour plasma glucose, fasting plasma glucose, triglycerides, and HDL cholesterol.(8)

In children, it is less clear how sedentary behaviour relates to cardiovascular and metabolic health. There is cross-sectional evidence that sedentary behaviours, such as TV viewing relates to cardiometabolic risk,(9,10) but these cross-sectional relationships are not always independent of MVPA, especially when sedentary behaviour and MVP are measured objectively,(11) raising the possibility that research based on non-objective measurements is biased. However, cross-sectional evidence may be explained by reverse causation, for example there are indications that body weight status can predict sedentary behaviour but sedentary behaviour may not predict future obesity in adults.(12) There is very little work done on the longitudinal relationships of objectively measured sedentary behaviour and cardio-metabolic health indicators in children. Such evidence will provide clues as to whether sedentary behaviour should be targeted separately to MVPA to protect and improve children's health. If sedentary time is found to be independently associated with cardio-metabolic risk in children, UK physical activity recommendations should explicitly address sitting in addition to recommending 60 minutes of MVPA a day. Such recommendations currently exist in guidelines in USA and Canada(13) and Australia,(14) where it is recommended that children limit their TV viewing time to less than 2 hours per day.

The main purpose of the proposed project will therefore be to study the longitudinal associations between sedentary behaviour and cardio-metabolic risk factors in children with an emphasis on the interactions between MVPA. Specific objectives would be:

* To examine the association of sedentary behaviour (assessed by questionnaire and accelerometer) in earlier childhood with variation in fasting blood glucose, insulin & lipids assessed at age 15 and 17 years.

. To examine the extent to which any of these associations are mediated by adiposity

. To examine whether associations of sedentary behaviour with these metabolic risk factors varies by whether the person has high or low levels of MVPA

Manos Stamatakis is applying for a Wellcome Trust senior career scientist fellowship to address these issues using data from a number of cohort studies and National cross-sectional surveys. These are likely to include (permissions either obtained or currently being sought) the Health Survey for England, Whitehall II and British Women's Heart and Health Study. One overall aim is to examine how patterns of sedentary behaviour and their associations vary by age group. Relevant analyses in ALSPAC as one part of his planned work for this fellowship. This will use data already available/funded in ALSPAC, including collected accelerometer data (Chris Riddoch grants) and fasting blood sample data (Debbie Lawlor grants) and will not require new data collection or bio-assays.

This application has been discussed with Prof C Riddoch & we would work in close collaboration with him & with Professors S Blair & R Pate who are applicants on the grant that funds the accelerometer data.

Methods

All applicants will develop the analysis protocol, in collaboration with S Blair & R Pate

DAL will put together the dataset

MS will complete analyses

All applicants will contribute to papers for publication

References

1. Katzmarzyk PT, Church TS, Craig CL, Bouchard C. Sitting Time and Mortality from All Causes, Cardiovascular Disease, and Cancer. Med Sci Sports Exe. 2009;41:998-1005.

2. Stamatakis E, Hamer M, Dunstan DW. Television and other screen-based entertainment time and cardiovascular events: population-based study with ongoing mortality and hospital events follow up. Under Review

3. Stamatakis E, Hirani V, Rennie K. Moderate-to-vigorous physical activity and sedentary behaviours in relation to body mass index-defined and waist circumference-defined obesity. Br J Nutrit 2009;101:765-773.

4. Frank LD, Martin A. Andresen MA, et al. Obesity Relationships with Community Design, Physical Activity, and Time Spent in Cars. Am J Prev Med 2004;27:87-96.

5. Jakes RW, Day NE, Khaw KT, et al. Television viewing and low participation in vigorous recreation are independently associated with obesity and markers of cardiovascular disease risk: EPIC-Norfolk population-based study. Eur J Clin Nutr. 2003;57:1089-1096.

6. Healy GN, Dunstan DW, Salmon J, et al. Objectively Measured Light-Intensity Physical Activity Is Independently Associated With 2-h Plasma Glucose. Diabetes Care. 2007;30:1384-1389.

7. Chang PC, Li TC, Wu MT, et al. Association between television viewing and the risk of metabolic syndrome in a community based population. BMC Public Health 2008;8:193 doi: 10.1186/1471-2458/8/193.

8. Healy GN, Dunstan DW, Salmon J, et al.: Television time and continuous metabolic risk in physically active adults. Med Sci Sports Exerc 2008, 40:639-645

9. Ekelund, U; Brage, S; Froberg, K; et al. TV viewing and physical activity are independently associated with metabolic risk in children: The European Youth Heart Study. PLoS Medicine 2006; 3: 2449-2457.

10. Martinez-Gomez, D; Tucker, J; Heelan, KA; et al. Associations Between Sedentary Behavior and Blood Pressure in Young Children. Archives of Pediatrics & Adolescent Medicine 2009, 163 (8): 724-730.

11. Mitchell JA, Mattocks C, Ness AR, et al. Sedentary Behavior and Obesity in a Large Cohort of Children. Obesity 2009; 17: 1596-1602

12. Ekelund U, Brage S, Besson H, Sharp S, Wareham NJ. Time spent being sedentary and weight gain in healthy adults: reverse or bidirectional causality? Am J Clin Nutr. 2008;88:612-617.

13. American Academy of Pediatrics, Committee on Public Education. Children, adolescents, and television. Pediatrics. 2001;107:423-426.

14. Australian Government, Department of Health and Ageing. Australia's physical activity recommendations for 5-12 tear olds. Department of Health and Ageing 2004, Canberra, Australia.