In we present the baseline characteristics of participants in both studies. The large majority of participants in the Collaborative study were male; the Collaborative study participants were somewhat older at baseline that those in the Main study. Combining the cohorts, there were 1,100 (73.2%) men and 403 women aged 16-35 years (mean 27.9 years) at study induction. Around three-quarters of this study sample were normal or underweight, just under one quarter were hypertensive, almost two thirds were current smokers, half were in a manual social class and almost two thirds were not regular drivers.
A total of 55,525 person-years of follow-up (median follow-up 39.6 years), gave rise to 255 deaths (194 in Main, 61 in Collaborative), 103 (82 and 21, respectively) of which were ascribed to CVD. In we present the relations of pre-middle age risk factors with total mortality. In age- and sex-adjusted analyses, obese study participants experienced greater mortality risk than their normal-weight counterparts. The suggestion of a modest elevated risk in the overweight group resulted in some evidence of an incremental effect across these weight categories (p for trend: 0.025). Lower FEV1 and FVC, current smoking, higher alcohol consumption, manual social class and being without a car were also associated with elevated mortality rates. There was a suggestion that increased systolic blood pressure and bronchitis conferred elevated risk, but associations were of borderline statistical significance and the latter was based on very few deaths in the exposed group. These gradients were very little altered on adjustment for markers of socioeconomic position (car use/ownership and social class). On mutual adjustment, the associations with total mortality for obesity, FEV1, current smoking and alcohol intake remained at conventional levels of statistical significance.
Hazards ratios (95% confidence intervals) for the relation of risk factors with all-cause mortality (N=1503)
In we depict the associations between risk factors pre-middle age and later CVD mortality. Lower FEV1 and FVC, current smoking, and higher alcohol consumption were associated with later risk CVD mortality after controlling for age and sex. There was also a suggestion of elevated CVD rates in persons with higher measured systolic and diastolic blood pressure, those who met the definition for hypertension, and in the lower occupational social classes although statistical significance was not seen. When we further adjusted for socioeconomic position there was again little evidence of attenuation of these effects estimates, although mutual adjustment led to some confidence intervals including unity. Hazards ratio across the smoking groups remained incremental (p for trend: <0.001).
Hazards ratios (95% confidence intervals) for the relation of risk factors with cardiovascular disease mortality (N=1503)
We carried out sub-group analyses of only Collaborative study participants, who had blood cholesterol measurements at baseline (374 individuals). Higher cholesterol was weakly associated with both total mortality (61 deaths) (HR 1.23; 95% CI: 0.94 - 1.60) and CVD mortality (21 deaths) (HR 1.38; 95% CI: 0.88 - 2.16) in multiply-adjusted analyses and statistical significance was not attained. We found very similar results comparing effect estimates for all other variables in the multiply-adjusted model including and excluding plasma cholesterol.
We also examined the relation of all the above risk factors with mortality due to cancers from all sites (87 deaths). Lower diastolic blood pressure, poorer lung function, current smoking, higher alcohol consumption and lower socio-economic status were all predictive in age- and sex- adjusted analyses. Some attenuation was apparent following mutual adjustment (results not shown but available upon request). To assess any effect modification due to high smoking prevalence in this population, we performed analyses separately for current and non-current smokers. Effect estimates were similar in each group. Further, all analyses were repeated on the subset of study members with no missing data (n= 1,356) and, again, results were found to be very similar to those reported here using imputed data.