A Randomized Trial of a Low-Fat Diet Intervention on Blood Pressure and Hypertension: Tertiary Analysis of the WHI Dietary Modification Trial

Abstract

Background: This post hoc analysis determined if the Women's Health Initiative (WHI) Diet Modification intervention (DM-I) resulted in a significantly different rate of incident hypertension (HTN), as well as longitudinal changes in blood pressure.

Methods: Participants were 48,835 postmenopausal women aged 50-79 years who were randomly assigned to either the intervention or comparison group. HTN was defined as self-report of treated HTN collected semiannually or blood pressure ≥140/90mm Hg at one of the annual follow-up clinic visits.

Results: After a mean follow-up of 8.3 years, and among those who did not have HTN at baseline (n = 31,146), there were 16,174 (51.9%) HTN cases and those assigned to the intervention group had a 4% lower overall risk of developing incident HTN (hazard ratio (HR): 0.96, 95% confidence interval (CI): 0.93-0.99). Although the risk of HTN was lower in the DM-I group in the first few years, the HR became greater than 1 after year 5 (P-trend < 0.01). Similarly, randomization to the DM-I arm resulted in a small but significantly lower average systolic blood pressure (SBP) at 1 year of follow-up (-0.66mm Hg, 0.44-0.89) that increased over the following 8 years (0.16mm Hg/year, 0.11-0.21), such that any early benefit was eliminated by year 5 and a minimal deleterious effect emerged by year 7.

Conclusion: Randomization to an intensive behavioral dietary modification program aimed at a lower total fat intake is not associated with sustained reductions in blood pressure or risk of HTN in postmenopausal women.

Clinical trial registration: url http://www.clinicaltrials.gov, unique identifier nct00000611.

Trial registration: ClinicalTrials.gov NCT00000611.

Keywords: blood pressure; diet; hypertension; trial; women..

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Figures

Figure 1.

Participant flow in the Dietary Modification Trial.

Figure 2.

Mean longitudinal effect of randomization to the DM-I arm compared to DM-C on systolic blood pressure, diastolic blood pressure, and pulse pressure. Estimate (95% CI) is from a linear mixed effects (LME) regression model shown by a solid (dotted) lines. The LME model included the corresponding baseline BP measurement as a covariate, a cubic polynomial to model time since randomization, an indicator variable for randomization group, an interaction term for randomization group × time (linear), along with a random intercept and random slope for time (linear). To confirm the LME model was reasonable, estimates for mean BP (95% CI; bowties) were also computed from a classical repeated measures model, where annual visits were coded categorically, and therefore do not assume a cubic relationship with time, nor a linear intervention effect.

Figure 3.

Kaplan–Meier estimates for incident hypertension during the intervention period by DMT arm. Solid black line, intervention group; dashed black line, control group.