ABSTRACT
OBJECTIVES: Our study compared 2 whole grain oat-based cereals with 2 refined grain wheat-based cereals to determine their effects on the need for antihypertensive medications in people with high blood pressure (BP).
STUDY DESIGN: This 12-week, randomized controlled parallel-group trial with 6 weeks of voluntary follow-up was designed to investigate the antihypertensive effects of oats. After 4 weeks of baseline feeding, medication dose was maintained or reduced by half or completely throughout the middle 4 weeks of the study. In the final 4 weeks, participants continued cereal consumption; medication was adjusted according to the protocol.
POPULATION: Men and women (n = 88) being treated for hypertension with a mean baseline BP below 160/100.
OUTCOMES MEASURED: Primary study outcomes included change in SBP and DBP as well as antihypertensive medication reduction. Secondary measures included blood lipid, fasting glucose, and insulin levels and side effects related to elevated BP and increased dietary fiber intake.
RESULTS: Seventy-three percent of participants in the oats group versus 42% in the control group were able to stop or reduce their medication by half. Treatment group participants whose medication was not reduced had substantial decreases in BP. The oats group experienced a 24.2–mg/dL reduction in total cholesterol levels, a 16.2–mg/dL decrease in low-density lipoprotein cholesterol levels, and a 15.03–mg/dL drop in plasma glucose levels vs controls.
CONCLUSIONS: Results suggest that a diet containing soluble fiber–rich whole oats can significantly reduce the need for antihypertensive medication and improve BP control. Considering the lipid and glucose improvements as well, increased consumption of whole oats may significantly reduce cardiovascular disease risk.
KEY POINTS FOR CLINICIANS
- Whole oats, when supplemented daily, significantly reduced antihypertensive medication need and improved blood pressure control over the 12-week intervention.
- Whole oats improved blood lipid and fasting glucose levels and reduced the incidence of overall study-related side effects.
- Significantly increasing whole oat consumption may greatly reduce risk for cardiovascular disease in hypertensive patients.
Since the initial use of antihypertensive medications in the 1940s, they have been the traditional approach to treatment essential hypertension. Many of these pharmacologic agents, however, are costly and are associated with substantial adverse effects. As a result, interest has been increasing in alternative methods to prevent and treat hypertension. Clinical trials using dietary interventions for the alleviation of hypertension and observational studies have suggested that a number of foods and specific food components may exert an antihypertensive effect.1-5 Other research, however, has shown no effect.6-10 Studies specific to oats or cereal fibers have also provided mixed results. Observational studies have noted a reduction in blood pressure (BP),11 but the few clinical trials conducted to date have shown no effect.12
Selected whole grains are known to be good sources of soluble fibers. Previous research trials have demonstrated that these fibers can effectively reduce plasma insulin concentrations and provide other health benefits.13,14 Additionally, elevated insulin levels have been implicated in the etiology of hypertension.15 Based on this potential biologic mechanism and the previously inconsistent findings, we conducted a 12-week trial to evaluate the clinical effects of soluble fiber–rich whole oat cereals when added to the diet of hyperinsulinemic patients medicated for essential hypertension.
Methods
Study sample
Participants were recruited from a database of treated hypertensive patients provided by a local health maintenance organization (HealthPartners). Initial letters describing the study were mailed to 8000 potential participants. Of these, 524 people responded to the mailing and agreed to a telephone screen to determine eligibility. Among respondents, 212 passed the initial phone screening and were invited to our research clinic (Hypertension and Cholesterol Research Clinic at the University of Minnesota Medical School) for a BP screening and general physical. For inclusion in the study, average screening BP readings (2 sets of readings within 7 days) taken by our team physician could not exceed 160/100. Table 1 lists exclusion criteria. The study protocol was reviewed and approved by the University of Minnesota Human Subjects Committee of the Institutional Review Board.
Eighty-eight volunteers (45 men and 43 women) aged 33 to 67 years met all inclusion criteria and provided written informed consent. All participants had a history of essential mild or moderate hypertension (BP 120/80 to 160/100 mm Hg), and were treated with no more than 1 antihypertensive medication (excluding -adrenergic receptor blocking agents) and/or 1 diuretic medication for at least 1 month before enrollment. Eighty participants were treated with a single antihypertensive medication; 8 required an antihypertensive drug and a diuretic medication to manage their BP. Individuals taking beta blockers were excluded from the study because they often take medications prescribed for more serious cardiovascular conditions, such as cardiac arrhythmias, and medication reduction would be inappropriate under such circumstances. Participants’ primary physicians were also consulted concerning participation and study-related medication changes.