The effect of a 12 week walking intervention on markers of insulin resistance and systemic inflammation

Abstract

Objectives

The purpose of the present study was to determine whether a community-based walking intervention, using pedometers, is effective in reducing systemic inflammatory markers.

Methods

Participants (age = 49(8.9)) were recruited in Glasgow, United Kingdom, from August to December 2006 and were randomly assigned to a control (n = 24; 6 males, no change in walking) and intervention group (n = 24; 5 males gradually increasing walking by 3000 steps/day on 5 days of the week). Blood samples were collected at baseline, and after 12 weeks, and analysed for glucose, insulin, high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), soluble IL-6 receptor (sIL-6R), tumour necrosis factor-alpha (TNF-α) and soluble TNF receptors I and II (sTNFR1 and sTNFRII).

Results

In the control group baseline step counts were 6356 (2953) steps/day and did not change (P > 0.05) after 12 weeks, 6709 (2918) steps/day. The intervention group increased (P < 0.001) step count from 6682 (3761) steps/day at baseline to 10182 (4081) steps/day at 12 weeks. Over the 12 week period there was no change in any other variables measured, in either control or intervention group.

Conclusion

We conclude that the current community-based intervention did not affect systemic markers of inflammation or insulin sensitivity.

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.