Five-year blood pressure trends and regression-to-the-mean in an industrial population

To determine trends in blood pressure (BP) and assess the statistical phenomenon of regression to the mean we performed sequential examinations in an industrial population.

All the employees in an industrial plant were examined. Height, weight, body mass index (BMI) and blood pressure were measured using standardised techniques successively for 5 years as part of annual medical check-up of these employees. All the male employees (n=145) were targeted in the first year of which 122 (84.1%) were examined. These numbers declined to 121, 99, 90 and 87 in subsequent years respectively due to employee attrition. Trends in levels of systolic and diastolic BP and hypertension prevalence were examined using standard regression analysis, least-squares regression and graphic analyses using a commercially available statistical programme.

The mean age 31.3 +/- 5.9 years (range 23-41). The mean height was 1.68 + 0.06 m, weight 60.0 + 9.1 kg and BMI 21.2 +/- 3.1 kg/m2. 18 subjects (14.8%) were overweight. From the first to the fifth year, respectively, BMI increased from 21.2 +/- 3.1 kg/m2 to 21.3 +/- 3.9, 21.9 +/- 3.0, 22.3 +/- 3.0 and 22.6 +/- 2.9 kg/m2 (r = 0.93, p = 0.011), systolic BP declined from 127.1 +/- 13.5 to 125.7 +/- 15.4, 125.5 +/- 12.9, 125.0 +/- 12.6 and 124.9 +/- 14.0 mm Hg (r = -0.60, p = 0.034) while diastolic BP remained unchanged (r = 0.15). Prevalence of hypertension (> or =140 / > or =90) declined from 34.4% at baseline to 28.9, 28.3, 24.4 and 24.1% respectively (r = -0.948, p = 0.021).

A high prevalence of hypertension in observed in this young industrial cohort. Without treatment, the hypertension prevalence as well as mean systolic BP decline over time demonstrating the statistical phenomenon of regression to the mean.