Background
In the Netherlands, among men aged younger than 65 years, a quarter of all deaths is due to cardiovascular diseases (CVD) [
1]. Cardiovacular disease may not only lead to premature death, but also to decreased physical functioning and lower quality of life [
2]. Important precursors of CVD are obesity, hypertension, and an abnormal blood lipid profile. These abnormalities are caused to a large extent by an unhealthy lifestyle, such as unhealthy diet [
3], insufficient physical activity (PA) [
4], and smoking [
5]. Irrespective of other CVD risk factors such as age, male gender, family history, or low job control [
6], improving lifestyle will lower CVD risk. Effective lifestyle change strategies should be developed in order to prevent CVD.
Numerous trials have been performed among persons with an elevated CVD risk, assessing the effectiveness of interventions aimed at changing lifestyle [
7‐
9]. Different strategies have been evaluated, among which providing advice, exercise classes, a prescribed diet, and individual counseling. Advice alone was proven to be less effective than individual counseling in achieving long-term behavior change among adults with an elevated CVD risk [
8,
9]. Supervised exercise and diet alone may facilitate body weight loss [
10], but long-term behavior change is less likely if not combined with more intensive diet and PA modification therapy [
11], such as individual counseling. Nowadays, a frequently used counseling method is motivational interviewing (MI). Motivational interviewing was originally developed for changing addictive behaviors, but has also proven effective in lifestyle change [
12,
13]. Motivational interviewing is a client-centered, directive method for enhancing intrinsic motivation to change by exploring and resolving ambivalence, and is based on the principle that behavior change occurs in stages [
14]. During MI, determinants are addressed that have consistently proven associated with behavior change, such as attitude and self-efficacy [
15].
The workplace is an appropriate setting for investigating lifestyle interventions, since many adults of various socio-economic statuses, lifestyles, and risk profiles can be targeted at once. Moreover, in the working population, a lifestyle intervention will not only influence CVD risk. Improving diet and increasing PA may also lower absenteeism [
16]. Regular PA may increase work ability, due to its effects on cardiorespiratory and musculoskeletal capacity, factors that normally decline with age [
17]. However, in most workplace lifestyle intervention studies, the sustenance of health effects, which is necessary for permanent CVD risk reduction, was not determined, as the final follow-up measurement took place directly after the intervention had ended [
18,
19]. Recently, two workplace intervention studies were performed on the effectiveness of MI on lifestyle changes [
20,
21], showing that MI is more effective than providing health risk information only, and equally effective to group activities or computer-tailored advice. Again, in both studies, no long-term follow-up measurements took place.
In the Health under Construction study, we aimed to develop and evaluate a lifestyle intervention for construction workers with an elevated CVD risk in the Netherlands. In this population, most workers are male and over 40 years of age. In 2008, the prevalence of overweight and obesity among male construction workers who attended a periodical health screening at the occupational health service was higher than in the total Dutch adult male population; 63.8% versus 52.3% [
22]. According to the Framingham risk score [
23], 27.3% of male construction workers had a higher than moderate 10-year risk of coronary heart disease. In the Health under Construction study, we evaluated the short- and long-term effects on PA, diet, and smoking of a lifestyle intervention consisting of individual counseling using MI techniques among male workers in the construction industry with an elevated risk of CVD in the Netherlands.
Methods
Participants
All male construction workers aged 18-65 years, employed at different (>400) companies throughout the Netherlands, who had attended the voluntary periodical health screening at the occupational health service between January 2007 and February 2008 (59.4% of all invited), and who had an elevated risk of CVD (n = 4.058; 19.1% of all screened), were personally invited to the study. Elevated CVD risk was concluded if the worker's 10-year coronary heart disease risk was higher than moderate according to the Framingham risk score, and he additionally fulfilled at least one of the following criteria; body mass index (BMI) ≥ 30 kg/m
2; HbA1c ≥ 6.5%; consuming ≥ 35 glasses of alcohol per week; not meeting the Dutch PA guidelines; heart complaints; psychological complaints. The Medical Ethics Committee of the VU University Medical Center approved the study protocol. An extensive description of the study design is provided elsewhere [
24].
Randomization, blinding, and sample size calculation
The workers who consented to participate were pre-stratified for work type (blue-collar workers performing the construction work versus white-collar workers involved in administration and supervision), and individually randomized into the control or the intervention group, using Random Allocation Software (Version 1.0). After randomization, the research assistant notified each participant to which group he had been allocated. The investigator who performed the data analyses was blinded to the group allocation. Due to the study design, the intervention providers and participants could not be blinded. The sample size was based on PA; one of the main outcome measures of the study. To detect a 10% difference between the control and intervention group in the proportion of participants meeting none of both Dutch guidelines for moderate and vigorous intensity PA after 6 months, i.e. 38% in the control group and 28% in the intervention group, with a power of 80% and a 95% confidence interval (α = 0.05), 692 persons were needed at the first follow-up measurement.
Intervention and control condition
Over a period of 6 months, each participant in the intervention group had three 45-60 minute face to face and four 15-30 minute telephone contacts with an occupational physician or occupational nurse. This counselor applied a client-centered counseling style using MI techniques such as asking open questions, summarizing, carefully listening, supporting, and raising ambivalence. In the first session, a stepwise protocol had to be followed. First, the participant's CVD risk profile was presented and his current health status was discussed. Second, the participant decided to aim at PA and diet, or smoking. Third, the participant was encouraged to indicate advantages and disadvantages of current and 'desired' behavior. Fourth, the participant was asked to indicate his willingness, readiness, and perceived confidence in his ability to change on 10-point scales. Last, the participant set long- and short-term goals, and formulated implementation intentions [
25]. In the following counseling sessions, progress and barriers were discussed. The participants in the control group received usual care, consisting of brief oral or written information from the occupational physician about their risk profile, based on the periodical health screening results. To all participants of both intervention and control group, brochures were provided containing information on PA, healthy eating, smoking cessation, and CVD.
Outcome measures
At baseline and after 6 and 12 months, a questionnaire on PA, diet, and smoking was filled out. For measuring PA, we used the fairly reliable (r
spearman 0.58) and valid (r
spearman 0.45) Short QUestionnaire to ASsess Health enhancing PA (SQUASH)[
26]. By means of this questionnaire, we determined the number of minutes per week spent on two domains of PA, i.e. leisure time PA (walking, cycling, doing odd jobs, gardening), and sports activities. In addition, the total weekly amount of energy expended due to the activities in those two domains was estimated, by multiplying the total number of minutes spent on each activity by its metabolic equivalent- (MET-) value [
27] and summing all MET-minutes. With regard to diet, in line with the Short Questionnaire for Measuring Fruit and Vegetable Intake, the average weekly intake during the past month was determined for fruit (pieces) and vegetables (heated and raw; tablespoons). Moreover, consumption of alcohol (glasses), and snacks were assessed. The latter food group was defined as the sum of sweet (e.g. piece of pie), cold salty (e.g. handful of crisps), and warm salty snacks (e.g. piece of egg roll), eaten outside the regular meals. The food questionnaire was not validated but tested for face validity by an expert in nutrition and lifestyle change, and for comprehensibility by two construction workers. Current smoking status was defined as 'smoker' or 'non-smoker'. Furthermore, the participant was asked whether he had used nicotine replacement therapy or medication in case he had succeeded in smoking cessation. At baseline, the possible confounding variables age (years) and BMI were determined at the occupational health service. For determining BMI, body height (meters) without shoes was determined with the participant in standing position, his heels and head against the wall and his face in a horizontal plane. Body weight (kilograms) was measured without shoes and jacket, using a digital balance.
Data analyses
Data were analyzed using SPSS (Version 15.0, Chicago Ill). In the baseline questionnaire, all participants had indicated whether they would prefer to improve their dietary or PA behavior, or to quit smoking. Those who had indicated to prefer improving diet or PA (energy balance-related behaviors; EB) were analyzed separately from the ones who had indicated to prefer smoking cessation (SC). As a result of self selection, baseline differences between the intervention and control group may have arisen, possibly leading to confounding. Therefore, we checked for baseline differences between intervention and control group in age, BMI, smoking status and all of the outcome measures, within both the EB group and the SC group. To determine the effects at 6 months, linear and logistic regression analyses were done with the variable of interest as the outcome, and group allocation (intervention vs. control) as the independent variable, adjusted for the baseline value. The effects at 12 months were evaluated using the same method. In both the EB and SC group we checked for confounding by age and BMI, and for effect modification by variables that theoretically could modify the effect on the outcome measure of interest, i.e. age, BMI, smoking, work type, and marital status (partner/no partner). Effect modification was concluded in case the p-value of the interaction term was <0.1. Only participants for whom data were present on all three time points were included in the analyses. Additionally, in order to assess the intervention effects among participants who had adhered to the protocol, linear and logistic regression analyses according to the 'per protocol' principle were done, for the effects at 6 and at 12 months. Of the intervention group, only those who had completed five or more counseling sessions on one of both topics (diet and PA, or smoking cessation) were included in the analyses. Of the control group, only those participants were included who had indicated not to have received counseling sessions and/or tailored lifestyle advice from any type of care provider, either face to face, by telephone, or computerized, between baseline and 6 months.
Competing interests Statement
The authors declare that they have no competing interests.
Authors' contributions
IG performed the analyses and wrote the manuscript. KP wrote the original study protocol. KP, AB, VH and WM provided intellectual input and had a role in supervision. All authors read and approved the final manuscript.