Relative risk estimate in HEAT for walking

In 2010, a systematic review to derive a risk estimate to be used for HEAT for walking was carried out (1,2). The review found nine studies meeting the inclusion criteria. These studies were combined in a pooled-analysis to calculate an aggregated risk, weighted by sample size. The resulting relative risk estimate was 0.78 (95% CI: 0.64–0.98) for a walking exposure of 29 minutes, 7 days a week (or about 200 minutes per week), which was used for the first HEAT walking.

In 2013, an updated systematic review and meta-analysis for walking was carried out (3). To be included in this review, a study was required:

  • to be a prospective cohort study;
  • to report the level of regular walking or cycling (such as duration, distance or MET equivalent);
  • report all-cause mortality rates or risk reductions as outcome; and
  • report results independent of (that is, adjusted for) other physical activity.

A total of 8901 titles were identified, and 431 full texts were screened. Fourteen studies on walking and all-cause mortality met the inclusion criteria, yielding high quality scores of 7 to 9 out of 9 possible points on the Newcastle-Ottawa Quality assessment scale for cohort studies. A meta-analysis was carried out. Since the available studies used a range of different exposures, to conduct the meta-analysis it was necessary to estimate for each study the reduced risk at a common exposure level. For this purpose, the different walking exposures used in the studies were converted into MET-hours per week (assuming a linear dose-response relationship and an average intensity of 4.0 METs for walking if not otherwise stated). 11.25 MET-hours per week was used as common reference level for the risk reductions. This value was derived from the global physical activity recommendations as corresponding to the recommended level of at least 150 minutes of moderate-intensity physical activity per week (4) using 4.5 METs as an average for moderate-intensity physical activity. Using an average intensity 4.0 METs for walking, this exposure represents 168 minutes of walking per week. Depending on the shape of the dose–response curve used, a risk reduction of 10–11% was found.

For the HEAT walking, the advisory group also recommended using a linear dose–response curve based on a relative risk of 0.89 (CI 0.83–0.96) and applying a constant absolute risk reduction (5). The sensitivity of the results to various possible shapes of dose–response relationships was tested. The differences between the various curves were small and the difference in the final risk estimate was no more than 6%.

Sources
  1. Kahlmeier S et al. Health economic assessment tools (HEAT) for cycling and walking. Methodology and user guide. Copenhagen: WHO Regional Office for Europe; 2011 (http://www.heatwalkingcycling.org/ index.php?pg=archive, accessed 26 March 2014).
  2. Development of guidance and a practical tool for economic assessment of health effects from walking. Consensus workshop, 1–2 July 2010, Oxford, United Kingdom. Background document: summary of literature reviews and issues for discussion. Copenhagen: WHO Regional Office for Europe; 2010.
  3. Development of the Health Economic Assessment Tools (HEAT) for walking and cycling. Consensus workshop: meeting background document. Bonn, 1–2 October 2013. Copenhagen: WHO Regional Office for Europe; 2014.
  4. Global recommendations on physical activity for health. Geneva: World Health Organization; 2010 (http://www.who.int/dietphysicalactivity/factsheet_recommendations/en/index.html, accessed 26 March 2014).
  5. Development of the Health economic assessment tools (HEAT) for walking and cycling. Consensus workshop: meeting report. Bonn, 1-2 October 2013. Copenhagen, WHO Regional Office for Europe, 2014.