The effect of a 12 week walking intervention on markers of insulin resistance and systemic inflammation☆
Introduction
Chronic systemic low-grade inflammation, defined as a two to four fold elevation in circulating levels of pro-inflammatory and anti-inflammatory cytokines (Bruunsgaard, 2005), has in recent years emerged as a major player in the aetiology of several chronic diseases, which are major causes of mortality in the western world. Of the many inflammatory markers interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-α) and C-reactive protein (CRP) are amongst the most commonly measured. The pleiotropic IL-6 has been demonstrated to be an independent risk factor for cardiovascular mortality (Pedersen, 2007, Tzoulaki et al., 2005) and is also involved in the development of insulin resistance (e.g. Bastard et al., 2002). The biological activity of IL-6 can be mediated by levels of its soluble receptor (sIL-6R) which has also been recently shown to be involved in the development of many diseases such as inflammatory bowel disease, peritonitis, rheumatoid arthritis, asthma and colon cancer (Scheller et al., 2006). The acute phase protein CRP has a pro-inflammatory effect and has been well established as a risk factor for cardiovascular disease, hypertension and stroke (Pearson et al., 2003). The cytokine TNF-α has been shown to have a direct role in the metabolic syndrome by inducing insulin resistance (Hotamisligil et al., 1993), a pre cursor for the metabolic syndrome and type 2 diabetes. High levels of TNF-α are also associated with an increased risk of atherosclerosis and myocardial infarction (Ridker et al., 2000). However, the short half-life of TNF-α in the circulation has also led to an increase in the number of studies investigating its soluble receptors. The degree to which these inflammatory markers affect insulin resistance can be measured by fasting levels of glucose and insulin, and the subsequent calculation of the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR).
Physical activity has long been prescribed to reduce the incidence of disease. A number of studies have shown that exercise interventions involving cycling, running, swimming and resistance exercise can reduce markers of inflammation (Goldhammer et al., 2005, Schumacher et al., 2006, Fairey et al., 2005, Kohut et al., 2006, Mattusch et al., 2000, Smith et al., 1999, Straczkowski et al., 2001, Tsukui et al., 2000), although several other investigations have found no change in inflammatory markers after similar exercise interventions (Ferrier et al., 2004, Hammett et al., 2004, Hammett et al., 2006, Kelly et al., 2004, LeMaitre et al., 2004, Marcell et al., 2005, Nicklas et al., 2004). The differing outcome of such studies may depend on the form/intensity/duration of exercise performed, whether concomitant dietary changes also occur, or the population status (e.g. patients with diabetes, obesity, cardiovascular disease/individuals with elevated levels of inflammation vs. healthy individuals). However, no clear pattern emerges.
Walking has been suggested to be the most likely form of exercise to increase physical activity (Hillsdon and Thorogood, 1996, Ogilvie et al., 2007) as it is accessible to most individuals with little risk of injury and can be accumulated into daily routine (Morris and Hardman, 1997). Controlled laboratory-based walking interventions, with concomitant restricted calorie intake, have previously been shown to decrease systemic levels of IL-6 and hsCRP (Balagopal et al., 2005, You et al., 2004, Roberts et al., 2006) with similar results found in a small participant group (n = 10) when no dietary changes occurred (Starkweather, 2007). There are currently no studies, to the authors' knowledge, that have investigated the effects of an increase in physical activity through walking, delivered in a community setting, on the chronic inflammatory processes.
The purpose of the present study, therefore, was to investigate the effectiveness of a community based walking intervention on systemic inflammatory markers in participants recruited from the local population. We hypothesised that an increase in physical activity would result in a decrease in markers of inflammation such as hsCRP, IL-6, TNF-α and their soluble receptors.
Section snippets
Participants
The current study was set in the community surrounding a West of Scotland university. Participants were recruited within a 1.5 km radius of the university in the period between August and December of 2006 using mail drops, local newspaper adverts and posters (placed in physicians' surgeries and shops within the study area). The criteria for inclusion within the study were: independently ambulatory, English speaking and between the ages of 18–65 years. Only individuals who were self-classified
Subject characteristics
Participants in the intervention group successfully increased (P < 0.001) their step count by 3300 (2215) steps/day while there was no change in the step count of the control group (Table 1). The goal of the intervention was to achieve an increase of 3000 steps/day on at least 5 days of the week and, on average, participants actually achieved an extra 3000 steps/day on 7 days of the week. At baseline there were no differences in the age, weight, BMI, body fat, waist-to-hip ratio or blood pressure
Discussion
Chronic low grade inflammation has been implicated in the aetiology of several chronic inflammatory diseases (Bruunsgaard, 2005) and the identification of effective therapies to reduce their incidence is clearly important. Regular physical activity has long been promoted as central to this objective and has been the focus of much research (e.g. Haskell et al., 2007). The current study, therefore, investigated the effects of an increase in physical activity through walking on systemic markers of
Conclusions
In conclusion a graduated 12 week walking programme in a community setting did not result in any changes in systemic markers of chronic low grade inflammation. This may be due to poor adherence during unsupervised exercise, insufficient exercise intensity/duration or insufficient duration of the intervention to result in positive anti-inflammatory effects. More community-based studies are required to determine the effects of different exercise intensity/duration on reducing chronic low grade
Conflict of interest statement
The authors declare that there are no conflicts of interest.
Acknowledgments
We would like to acknowledge the assistance of Rona Sutherland, Martha Paisi and Martin Watson in the data collection.
Funding: The Scottish Physical Activity Research Collaboration (SPARColl) is managed by NHS Health Scotland and funded by the Scottish Government Health Department.
Ethical approval: University of Strathclyde Ethics Committee (UEC0506/56).
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Trial registration — Current controlled trials ISRCTN88907382 [controlled-trials.com].