Background Recent declines in cardiovascular mortality in Ireland and other developed countries are partially attributable to favourable secular trends in blood pressure (BP). However the underlying causes of these BP trends are not well defined. In particular, the contribution of changes in the dietary and other lifestyle determinants of population BP levels is unclear. We examined changes in distribution and determinants of systolic blood pressure (SBP) in middle-aged Irish adults over a 12 year period

Methods Data are from two cross-sectional studies of men and women aged 47-73 years recruited from 17 General Practices in Cork and Kerry (N = 1018, response rate 70%) and from one large General Practice in Cork (N = 2047, response rate 67%) in 1998 and 2010 respectively. Similar procedures were used at both time points, including recruitment methods, exclusion criteria, health and lifestyle questionnaire, dietary assessment (food frequency questionnaire [FFQ]) and physical examination (height, weight and blood pressure). Dietary quality was assessed using the Dietary Approaches to Stop Hypertension (DASH) score constructed from the FFQ: higher scores indicating healthier diets. Changes in mean SBP were examined in linear regression models and are presented as means (95% CI).

Results Mean SBP fell by 7.1 mmHG (138.0, 130.9) in men and 4.7 mmHG (133.0, 128.3) in women between 1998 and 2010. Adjusted for age, gender and education mean SBP, was 5.8 mmHG (-7.3, -4.5) lower in 2010 than in 1998. Average BMI increased from 27.8 (4.0) to 29.1 (4.1) in men and from 27.4 (4.6) to 28.0 (5.1) in women. By contrast diet quality improved over the period in men and women from 22.5 (4.4) to 27.6 (5.6) and from 23.5 (4.7) to 30.1 (5.6) respectively. Significant trends in physical activity (favourable), smoking (favourable), and alcohol intake (unfavourable) were observed. The proportion of the sample with doctor diagnosed hypertension increased from 25% to 29% over the 12 year period. Adjusting for age, gender, education, BMI, smoking and alcohol the change in mean SBP remained relatively unchanged. Adjusting for DASH diet score the mean SBP change it was reduced to 4.1 mmHG (-6.5, -1.7) and on further adjustment for doctor diagnosed hypertension it was reduced to 3.9 mmHG (-6.3, -1.6).

Discussion The findings suggest that average blood pressures levels in the population are falling, despite increasing prevalence of obesity. Much of the change is due to improvements in diet.