No reduction in C-reactive protein following a 12-month randomized controlled trial of exercise in men and women

Abstract

Low-grade systemic inflammation is suggested to play a role in the development of several chronic diseases including cancer. Higher levels of physical activity and lower adiposity have been associated with reduced levels of markers of systemic inflammation, such as C-reactive protein (CRP); however, reductions in CRP have not been observed consistently in randomized controlled trials of exercise.

Purpose

To examine the effect of a 12-month aerobic exercise intervention on CRP levels in men and women.

Methods

102 men and 100 women, sedentary and aged 40–75 years, mean BMI of 29.9 and 28.7 kg/m², respectively, were randomly assigned to a 12-month moderate-to-vigorous aerobic exercise intervention (6 d/wk, 60 min/d, 60–85% maximum heart rate) or control group. Fasting blood samples were collected at baseline and at 12-months. CRP levels were measured by high-sensitivity latex-enhanced nephelometry.

Results

At baseline, CRP was 1.16 mg/L and 2.11 for men and women, respectively, and CRP was correlated with percent body fat (r=0.48, p ≤0.001), BMI (r=0.37, p ≤0.001) and aerobic fitness (r=−0.49, p ≤0.001). No intervention effects were observed for CRP in men or women, or when stratified by baseline BMI (< 30 kg/m² vs. ≥ 30 kg/m²), baseline CRP (< 30 mg/L vs. ≥ 3 mg/L) or change in body weight, body composition or aerobic fitness.

Conclusion

A 12 month moderate-to-vigorous aerobic exercise intervention did not affect CRP levels in previously sedentary men or women with average-risk CRP values at baseline.

Introduction

Systemic inflammation has been implicated in the pathogenesis of several chronic diseases, including cancer (1–3). In relation to cancer, systemic inflammation is suggested to play a role in both tumor development and promotion (4). C-reactive protein (CRP) is a nonspecific acute-phase protein secreted by the liver that is considered a surrogate marker of chronic low-grade systemic inflammation. Systemic inflammation has been suggested to be an important mechanistic link between physical activity and cancer risk (5).

CRP is positively associated with body fat (6, 7) and negatively associated with physical activity (8–11), and cardiorespiratory fitness (VO₂max) (12–16) in observational studies. It is not clear whether improvements in cardiorespiratory fitness reduce CRP, and whether such an effect is mediated entirely by a reduction in body fat. The results of previous randomized controlled trials of exercise effects on CRP levels have been mixed (17–25).

This study investigated the effects of a 12-month aerobic exercise intervention on CRP, a proposed biomarker of cancer risk, in 202 previously sedentary adults. We hypothesized that those in the exercise group would have a significant improvement in aerobic fitness (VO₂max) and a subsequent reduction in CRP at 12-months compared to controls.

Materials and Methods

Design Overview

This study was a 12-month randomized controlled trial that compared the effect of a moderate-intensity exercise intervention to a usual lifestyle control program on biomarkers of colon cancer risk. Participants were men and women, 40–75 years who: were sedentary (i.e., < 90 min/wk of moderate-to-vigorous exercise in the past 3 months); had a normal exercise tolerance test; and had no serious medical conditions. Participants were recruited to a trial examining biomarkers of colon cancer risk, through media placements, flyers, a study web site, and referrals (2001–2004). 102 men and 100 women were enrolled. The study was approved by the Fred Hutchinson Cancer Research Center Institutional Review Board.

Laboratory Analysis

Blood samples were obtained following a 12h fast and stored at −70°C. Plasma CRP was measured by latex-enhanced nephelometry using high-sensitivity assays on the Behring Nephelometer II analyzer (Dade-Behring Diagnostics, Deerfield, IL) at the University of Washington (UW) Clinical Immunology Laboratory, by staff blinded to group assignment. Lower detection limits for CRP were 0.2 mg/L for CRP. The inter- and intra-assay coefficients of variations were 0.3% and 0.3%, respectively.

Demographics, anthropometrics and fitness

At baseline and 12-months, participants were evaluated for: demographics, medical history, weight, height, body composition measured by DEXA whole-body scanner (GE Lunar, Madison, WI) and cardiopulmonary fitness (VO₂max), measured by oxygen update during a maximal-graded treadmill test (Medgraphics, MN).

Intervention

The intervention was an aerobic exercise program (12 mos, 6d/wk, 60 min/d, at 60–85% of maximal heart rate, determined by the graded treadmill test) with both supervised facility (at least 3 d/wk) and home-based sessions. Exercisers and controls were asked during the trial not to change their dietary habits and controls were asked not to change their exercise habits.

Randomization and Statistical Analyses

Participants were randomly assigned to the exercise or control groups, blocked on sex and, among women, on menopausal status (pre- or peri- vs. postmenopausal) and current use (yes/no) of postmenopausal hormones.

Intervention effects were determined by generalized estimating equations for linear regression. Baseline CRP data were available for 195 participants. Participants with missing end-of-study CRP data (N=7) were not included in the analysis. Means and standard deviations are reported, except for the main outcome, CRP, where geometric means are reported to reduce the impact of outliers. Associations between CRP and baseline participant characteristics were examined using Spearman correlations. Secondary analyses examined intervention effects stratified by baseline BMI (< 30 kg/m² and ≥ 30.0 kg/m²), baseline CRP levels (< 3 mg/L vs. ≥ 3 mg/L), change in body weight (control, exercise: no change, ≤ 3 kg, or > 3 kg), change in body fat (control, exercise: no change, ≤ 2%, > 2%) or change in aerobic fitness (control, exercise: ≤ 5%, 5–15%, > 15%). Statistical analyses were performed using SAS software (version 9.1; SAS Institute Inc, Cary, NC).

Results

No differences between groups were noted at baseline (Table 1). Male and female exercisers averaged 370 (103 % of goal) and 295 (82% of goal) minutes per week, respectively. Aerobic fitness (VO₂max) increased by 11% (3.3 mg/kg/min) and 10.5% (2.5 ml/kg/min) among male and female exercisers, respectively, and decreased in both female and male controls (−6.3% and −1.8%, respectively, p< 0.001 comparing exercise to control for both genders). The effect of the intervention on body composition has been reported in detail (26). In brief, exercisers lost weight and body fat compared to controls both among men (−1.8 versus −0.1 kg, p=0.03 and −2.7 versus +0.2 %, p <0.001, respectively) and women (−1.4 versus +0.7 kg, p=0.008 and −1.8 versus −0.1 %, p=0.002, respectively). No differences were noted for dietary intake throughout the study.

Table 1.

Participant characteristics at baseline.

	Women		Men
	Exercisers N=49 Mean (SD) or N (%)	Controls N=51 Mean (SD) or N (%)	Exercisers N=51 Mean (SD) or N (%)	Controls N=51 Mean (SD) or N (%)
Age (years)	54.4 (7.1)	53.7 (5.6)	56.2 (6.7)	56.6 (7.6)
Race
White	42 (86)	47 (92)	48 (94)	48 (94)
Non-white	7 (14)	4 (8)	3 (6)	3 (6)
Menopausal status			NA	NA
HRT user	23 (47)	22 (43)
No HRT	10 (20)	11 (22)
Premenopausal	16 (33)	18 (35)
Height (cm)	164.0 (6.9)	165.5 (6.4)	178.4 (6.3)	179.8 (8.0)
Weight (kg)	78.0 (17.8)	77.9 (12.8)	94.8 (14.9)	97.4 (18.2)
BMI (kg/m2)	28.9 (5.5)	28.5 (4.8)	29.7 (3.7)	30.1 (4.8)
Body fat (%)	43.3 (7.2)	43 (6.8)	31.5 (6.4)	29.7 (6.0)
Total fat mass (kg)	34.4 (13.6)	33.9 (10.4)	30.3 (9.5)	29.0 (9.5)
VO2max (ml/kg/day)	23.8 (5.1)	24.8 (4.3)	30.1 (5.9)	30.3 (6.7)
Cigarette Use
Smoker	2 (4)	1 (2)	5 (10)	4 (8)
Non-smoker	47 (96)	50 (98)	46 (90)	47 (92)

^*1 female control, 1 male control, and 2 male exercisers were missing baseline DEXA.

^†T-test comparing baseline characteristics for female exercisers versus controls.

^‡T-test comparing baseline characteristics for male exercisers versus controls.

At baseline, CRP was correlated with percent body fat (r=0.48, p =0.001), BMI (r=0.37, p ≤0.001) and aerobic fitness (r=−0.49, p ≤0.001), with similar results for analysis limited to either men or women (data not shown). No intervention effects were observed for CRP in men or women overall (Table 2), or when stratified by baseline BMI (Table 3), baseline CRP (data not shown), change in aerobic fitness or change in body composition (data not shown).

Table 2.

Geometric means (95% confidence intervals) for the effect of exercise on CRP: differences at baseline and after 12 months of exercise intervention.

	Baseline					Follow-up
	Exercisers		Controls			Exercisers		Controls
	N	Geometri c mean (95% CI)	N	Geometri c mean (95% CI)	† P- value	N	Geometri c mean (95% CI)	N	Geometri c mean (95% CI)	P- value ‡
Men	4	1.16	4	1.16	0.99	4	1.23	4	1.01	0.29
	9	(0.92–1.46)	9	(0.87–1.55)		6	(0.95–1.60)	9	(0.77–1.33)
Women	4	2.08	4	2.16	0.87	4	1.87	4	2.16	0.65
	8	(1.48–2.91)	9	(1.57–2.97)		5	(1.35–2.59)	8	(1.57–2.98)

^†p-value for exercisers versus controls at baseline;

^‡p-value for changes from baseline to 12months, among exercisers versus controls, with adjustment for baseline values.

Table 3.

CRP levels at baseline and 12 months in exercise intervention and control participants: stratified by baseline BMI.

	Baseline				Follow-up
	n	Exercisers Geometric Mean (95% CI)	n	Controls Geometric Mean (95% CI)	n	Exercisers Geometric Mean (95% CI)	n	Controls Geometric Mean (95% CI)
Men
BMI < 30 kg/m2	26	0.85 (0.63–1.14)	26	0.89 (0.61–1.30)	22	0.82 (0.62–1.08)	26	0.74 (0.54–1.01) † p-value: 0.61
BMI ≥ 30 kg/m2	23	1.67 (1.24–2.25)	23	1.57 (1.03–2.39)	24	1.80 (1.25–2.59)	25	1.40 (0.92–2.15) † p-value: 0.38
Women
BMI < 30 kg/m2	29	1.32 (0.88–1.99)	30	1.60 (1.07–2.38)	28	1.27 (0.86–1.89)	29	1.59 (1.04–2.45) † p-value: 0.82
BMI ≥ 30 kg/m2	19	4.14 (2.68–6.39)	19	3.47 (2.20–5.47)	17	3.54 (2.33–5.38)	19	3.44 (2.29–5.16) † p-value: 0.73

^†P-value for difference in CRP changes from baseline to twelve months in exercise intervention versus control stratified by BMI group, controlling for baseline CRP values.

Conclusion

A 12-month randomized controlled aerobic exercise intervention resulted in improved cardiorespiratory fitness in both men and women. However, this improvement did not translate into a reduction in CRP. These findings are consistent with other randomized controlled trials of exercise alone (17–25) and a recent meta-analysis (27), which included five of these studies and reported a 12% improvement inVO₂max resulted in a non-significant 3% decrease in CRP. However, previous trials have been hampered by small sample size, use of a clinical population which may have altered CRP levels due to the underlying medical condition (23, 24), and type and duration of aerobic exercise intervention. The current study adds to the literature by examining this question in a large number (n=202) of healthy, sedentary middle-aged adults, using a year long exercise trial that achieved excellent adherence.

In our study, the exercisers lost weight and had a reduction in total body fat (26). A reduction in CRP has been reported with weight loss in randomized controlled trials of very low calorie diet interventions (28, 29), gastric bypass surgery (30) and lifestyle interventions (i.e. combined diet and exercise) (31, 32). However, the change in CRP may be contingent on the associated change in body weight with the interventions. In our study, the exercise groups did not experience significant weight loss (< 2.0 kg over 12-months).

Nevertheless, exercise is suggested to play an important role in reducing systemic inflammation beyond simply inducing weight loss. Lower cardiorespiratory fitness (VO₂max) is associated with higher CRP levels in cross-sectional studies (12–16). Therefore, examining the effect of a change in VO₂max on CRP would provide insight into the impact of aerobic exercise on CRP levels. You et al.(33) reported a 6% improvement in absolute VO₂max and reduction in CRP in a 6-month randomized controlled trial of combined hypocaloric diet and exercise versus no change with hypocaloric diet alone in 34 obese, postmenopausal women with similar reductions in body weight and body fat in both groups. However, in our study, female and male exercisers had statistically significant improvements in VO₂max, 10.5% and 11%, respectively, but no intervention effect on CRP was noted.

The baseline characteristics of participants may impact the effect lifestyle interventions on CRP. Our participants fell in the “average” risk category (1–3 mg/L, based on criteria from the American Heart Association). Reductions in CRP level with lifestyle interventions has been successful in studies of individuals with much higher baseline CRP values (i.e. > 5 mg/L) (32–35) or in more obese participants (i.e. BMI > 30–35 kg/m²) (31, 32, 34, 35). We found no change in CRP with stratified by baseline CRP level (i.e. < 3 mg/L or ≥ 3 mg/L) and BMI (i.e. < 30 kg/m² or ≥ 30 kg/m²). However, we have some unpublished data to support this, inasmuch as, in another study, women with a higher BMI (> 30 kg/m²), particularly, showed a reduction in CRP over 12 months following a similar intervention regime (P Campbell et al, submitted¹).

A limitation of this study was that it was designed to look at a number of proposed biomarkers of colon cancer risk. Therefore, individuals were recruited based on a number of baseline characteristics that did not include CRP levels. As a result, participants had low CRP levels at baseline. From the literature, it would suggest that exercise and/or weight loss may be more effective in those with higher initial CRP values. Also oral hormone replacement therapy (HRT) has also been shown to elevate CRP levels (36). Our sample included both pre- and postmenopausal women, and HRT users and non-users, with approximately half of the women in the trial were using HRT. The use of HRT may have counteracted reductions in CRP level due to a lifestyle intervention.

In conclusion, a 12-month randomized controlled trial of aerobic exercise in previously sedentary adults did not alter CRP, a marker of systemic inflammation, despite resulting in a significant improvement in aerobic fitness (VO₂max) and decrease in body weight and body fat. This suggests that exercise may have a greater role to play in those with higher initial levels of systemic inflammation, such as obese individuals.