Objective: To assess whether dietary intervention in free-living healthy subjects is effective in improving blood pressure levels.
Design: Open randomised, controlled trial.
Setting: Free-living healthy subjects in two rural villages in north-eastern Japan.
Participants: Five hundred and fifty healthy volunteers aged 40-69 years.
Interventions: Tailored dietary education to encourage a decrease in sodium intake and an increase in the intake of vitamin C and carotene, and of fruit and vegetables.
Main outcome measures: Blood pressure, dietary intake and urinary excretion of sodium, dietary carotene and vitamin C, and fruit and vegetable intake data were collected at 1 year after the start of the intervention.
Results: During the first year, changes differed significantly between the intervention and control groups for dietary (P = 0.002) and urinary excretion (P < 0.001) of sodium and dietary vitamin C and carotene (P = 0.003). Systolic blood pressure decreased from 127.9 to 125.2 mmHg (2.7 mmHg decrease; 95% confidence interval, -4.6 to -0.8) in the intervention group, whereas it increased from 128.0 to 128.5 mmHg (0.5 increase; -1.3 to 2.3) in the control group. This change was statistically significant (P = 0.007). In contrast, the change in diastolic blood pressure did not significantly differ between the groups. In hypertensive subjects, a significant difference in systolic blood pressure reduction was seen between the groups (P = 0.032).
Conclusion: Moderate-intensity dietary counseling in free-living healthy subjects achieved significant dietary changes, which resulted in a significant decrease in systolic blood pressure.