Health checks and coronary risk: further evidence from a randomised controlled trial

Subjects and methods AIMS

This study was established as a randomised controlled trial to answer two questions. Firstly, do health checks modify risk factors for coronary heart disease or other health related behaviours, or both? Secondly, are any particular benefits conferred by personalised feedback of plasma cholesterol concentration or coronary risk score, or both?

STUDY POPULATION

The study took place in two work sites in Glasgow. The main intervention site was a large engineering factory that employed just over 2600 people in 1991, when the study started. The other site, which provided the external control group, was an engineering and repair facility with a workforce of 290. Both workforces were predominantly middle aged male blue collar workers (skilled manual workers). Table R1 gives a breakdown of the age and sex distribution of the study samples. Although the proportion of women in the workforce was small, both sexes were included so that the study would reflect the operational realities faced by workplace health check programmes.

RECRUITMENT, INITIAL ASSESSMENT, AND RANDOMISATION

In the main intervention site 1600 subjects were randomly selected. Those working permanent night shifts were excluded because of practical difficulties. A total of 1381 subjects accepted the invitation, 10 of whom were excluded because they were participants in another coronary intervention study or were taking lipid lowering agents. Subjects with high plasma cholesterol concentrations (>7.8 mmol/l) or high blood pressure (>160 mm Hg systolic pressure or >100 mm Hg diastolic pressure) were referred to their general practitioner but remained as participants in the study.

We calculated that 200 subjects in each of the study groups would allow a difference in the mean change between any two groups of 0.3 of a standard deviation to be detected with 80% power at the 5% significance level. We selected a slightly larger sample size to allow for non-responders.

At the main intervention site 1371 subjects were allocated, by means of computer generated randomisation, to one of five groups. Each received different information and feedback.

Group 1 received health education without feedback on cholesterol concentration or risk score.

Group 2 received health education with feedback on cholesterol concentration but without feedback on risk score.

Group 3 received health education with feedback on risk score but not on cholesterol concentration.

Group 4 received a full health check: health education with feedback on cholesterol concentration and on risk score.

Group 5 acted as an internal control group, their intervention being delayed.

Two hundred and sixty one subjects from the other workforce acted as the external control group (group 6). Their intervention was also delayed.

All six groups were seen at enrolment (stage I), after five months (stage II), and after 12 months at the completion of the study (stage III). This timetable is illustrated in the figure. A common dataset was collected from participants at each visit. The data comprised sociodemographic data including age, sex, address, general practitioner, education, and occupation or employment; relevant details of family and personal medical history including height, weight, blood pressure (using a random zero sphygmomanometer, measured twice after resting for five minutes), and non-fasting plasma cholesterol concentration for both desk top and laboratory measurement; and health related behaviour including diet, alcohol intake, smoking, and exercise.

To minimise bias in self reported behaviour that might arise from a subject's desire to please an interviewer, data on smoking, drinking, and exercise were collected separately at each stage and replies analysed later for change (rather than asking the subjects for self reported changes).

Design of study

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The health education package was an interview backed up by written information. Each component of the health message and the feedback on risk score and cholesterol concentration was written and rehearsed by the counsellors to ensure consistency of advice. However, issues of most relevance to each subject were emphasised by the counsellors. When group allocation determined that feedback was not to be given on risk score or cholesterol concentration, or both, the counsellor and the subject remained blind to the relevant measurements.

The internal and external control groups were both assessed at stage I but received no health education, feedback, or written information. In this way groups 5 and 6 acted as control groups between stages I and II. We recognised that subjects in group 5 (internal control) were open to influences from colleagues because the messages given to other participants were being freely discussed in the workplace. The external control group did not have these influences. After five months (stage II) groups 5 and 6 were reassessed and provided with a full health check. Although delaying any intervention in these groups until the end of the study would have been advantageous from a scientific perspective, we judged this approach to be impractical as it might have led to poor participation at follow up.

ANALYSIS

The key baseline characteristics of the study groups were compared using one way analysis of variance or Kruskal-Wallis tests for continuous variables and χ² tests for categorical variables. The effect of the full health check was assessed by comparing changes over the five months between stages I and II in group 4 (full health check) and group 5 (internal control) and in group 4 and group 6 (external control). Comparisons were made separately with each control group because they came from different locations and a comparison of changes between the two control groups provides an indication of the degree to which the internal control group had taken up the health education messages that were being discussed in the workplace. Results were analysed on the basis of intention to treat, with nonattenders at stage II being deemed to have made no change (table 2). Two sample t tests or Mann-Whitney U tests were used for continuous variables, while χ² tests were used to compare the number who had made a positive change, no change, or a negative change for categorical variables.

In assessing the interventions and, therefore, the effect of feedback, analysis was carried out on the basis of intention to treat and then, separately, on subjects who had attended all stages (full attenders) (table 2). Changes over time from stages I to II were compared by one way analysis of variance or Kruskal-Wallis tests for continuous variables and χ² tests, as described above, for categorical variables. Follow up multiple comparisons were used with the Bonferroni correction to determine which groups differed significantly from which others.

The health check computer programme generated a risk score for immediate feedback based on a risk factor algorithm. However, for analytical purposes, and to facilitate comparison with other published studies, we considered it useful to use the more recently developed Dundee risk score as an outcome measure. The Dundee risk score is a well validated method of estimating reversible cardiac risk based on a score that runs from 1.5 to 50 derived from the subject's smoking habit, blood pressure, and blood cholesterol concentration.11

SUMMARY OF STUDY DESIGN

The study design achieved two objectives. Firstly, it created a narrow randomised controlled trial on the basis of intention to treat between group 4 (full health check) and group 5 (internal control) and separately between groups 4 and 6 (external control) over five months (stages I to II). Secondly, it allowed multiple comparisons between all the study groups to assess the impact of components of the health check including feedback of cholesterol concentration. This paper concentrates on these two issues between stages I and II. Changes in the workforce as a whole over a longer follow up period (until stage III) will be reported elsewhere.

EFFECTIVENESS OF THE HEALTH CHECK

Tables 3 and 4 summarise the comparison of 263 subjects in group 4 (full health check) and 233 subjects in group 5 (internal control) between stages I and II. The analysis was conducted on the basis of intention to treat. Changes in clinical measurements (plasma cholesterol concentration, diastolic blood pressure, and body mass index) were small. Although small, the change in mean cholesterol concentration was significantly higher in group 4 (0.16 mmol/l) than in group 5 (0.03 mmol/l) (difference in change 0.13 mmol/l (95% confidence interval for difference in change 0.02 to 0.22), P=0.02). There were no significant differences between the two groups for changes in Dundee risk score (P=0.21), diastolic blood pressure (P=0.71), or body mass index (P=0.16).

Changes in the prevalence of smoking were small and showed no significant difference between the groups (P=1.00) (table 4). Changes in reported exercise were large, but the proportion of participants who reported exercising less than 20 minutes aerobically three times a week at stage I who had increased above this level by stage II were similar in both groups (42% in group 4 and 37% in group 5, P=0.41). Changes in self reported alcohol consumption were large and showed significant differences between groups. Of those at stage I who were drinking above recommended limits (21 units weekly for men and 14 units weekly for women), 41% in group 4 and 17% in group 5 reduced alcohol consumption (P=0.001). All participants made some improvement in their diet. Significant differences were found for self reported increases in the consumption of fruit and vegetables (24% v 12%, difference 13% (6.2% to 19.2%), P<0.001) and self reported reductions in consumption of fat (30% v 9%, difference 21% (13.9% to 27.3%), P<0.001).

Tables 5 and 6 show the comparable set of results for group 4 (full health check) and 261 subjects in group 6 (external control). The pattern of results in tables 5 and 6 is similar to that in tables 3 and 4. In tables 5 and 6, however, the difference in mean change in Dundee risk score is significant (0.28 (-0.01 to 0.58), P=0.05), the difference in proportion increasing fruit and vegetable consumption is not significant (5.5%; P=0.12), and the difference in proportions increasing fibre consumption is significant (6.4% (1.0 to 11.8), P=0.02).

BENEFITS OF FEEDBACK OF CHOLESTEROL CONCENTRATION AND RISK SCORE

There were no differences between groups to suggest that feedback of cholesterol concentration or risk score had additional impact on any of the outcomes. All six groups were compared with each other to assess their impact on each outcome measure. To isolate the effect of feedback of cholesterol concentration we paid particular attention to detecting differences between group 1 (health education only) and group 2 (health education and cholesterol feedback) and between group 3 (health education and feedback on risk score but not cholesterol concentration) and group 4 (full health check). In the same way, we compared groups 1 and 3 and groups 2 and 4 to identify any additional benefits from feedback of risk score. Analysis was carried out on the basis of intention to treat, to determine the impact of feedback, and on full attenders, to maximise sensitivity to any effect of feedback.

Some differences were detected between the intervention groups and the control groups. For several categories of self reported dietary behaviour (table 7) each of the four intervention groups (groups 1-4) showed greater improvements than the internal control group (group 5). All four intervention groups reduced fat consumption significantly better than the internal control group. The differences between groups 5 and 2 were also significant for increases in fibre consumption and between group 5 and groups 2 and 4 for increase in fruit and vegetable consumption (P<0.005 in each case).

Group 4 showed an improvement in self reported alcohol consumption that was significantly larger than that in group 5 (P=0.001). None of these differences in outcomes, however, showed an enhanced effect from feedback of cholesterol concentration or risk score.