Heart rate, employment status, and prevalent ischaemic heart disease confound relation between cereal fibre intake and blood pressure

Cross sectional data from a survey of 2512 men aged 45-49 years were used to examine the confounding effects of heart rate, employment, and ischaemic heart disease (IHD) on the relation between cereal fibre intake and blood pressure. Daily cereal fibre intake (g/day) was associated with systolic pressure (r = -0.053, p less than 0.01), diastolic pressure (r = -0.057, p less than 0.01), and heart rate (r = -0.071, p less than 0.01). The associations were strengthened in employed men and inapparent in unemployed men. Unemployed men had more IHD than employed men. Persons with any manifestation of IHD had significantly higher blood pressure and heart rates but ate less cereal fibre (7.0 v 7.9 g/day, p less than 0.001) than those without IHD, regardless of employment status. In employed men, after adjustment for age, body mass index, prevalent IHD, and heart rate, systolic pressure changed -0.186 mmHg (95% CI = -0.362, -0.009) and diastolic pressure changed -0.111 mmHg (95% CI = 0.228, 0.005) for each gram of cereal fibre eaten daily. The association between cereal fibre and blood pressure was inapparent in unemployed men. Heart rate, employment, and prevalent IHD confound the association between cereal fibre intake and blood pressure. Future work concerning this relationship will have to account for the effects of these variables.