Original Article
Epidemiological
Vegetable Protein and Fiber from Cereal Are Inversely Associated with the Risk of Hypertension in a Spanish Cohort

https://doi.org/10.1016/j.arcmed.2006.01.007Get rights and content

Background

Some cross-sectional studies suggest that fiber and protein intake can be associated with lower levels of blood pressure, but results from prospective cohorts are scarce and none has been conducted outside the U.S.

Methods

The SUN cohort followed-up prospectively 5880 Spanish men and women older than 20 years of age, all university graduates. Dietary information was gathered at baseline with a previously validated semiquantitative food frequency questionnaire. New cases of medically diagnosed hypertension (HT) were identified through responses to a mailed questionnaire after at least 2 years from recruitment.

Results

One hundred and eighty new cases of HT were ascertained after a median follow-up of 28 months. After adjustment for potential confounders and several dietary factors, participants in the highest quintile of vegetable protein intake had a lower risk of incident HT compared with those in the lowest quintile [hazard ratio (HR) = 0.5, 95% confidence interval (CI) 0.2−0.9, p for trend = 0.06]. Similarly, fiber from cereals was inversely associated with a lower risk of HT (HR comparing fifth vs. first quintile = 0.6, 95% CI 0.3–1.0, p for trend = 0.05). Risk reduction was more important among men and obese and older individuals. Total or animal protein and total fiber as well as fiber from other sources different from cereal were not associated with the risk of HT.

Conclusions

In this Mediterranean cohort, dietary intake of vegetable protein and fiber from cereals was associated with a lower risk of HT when other nutrients were also taken into consideration.

Introduction

The most recent statement on the primary prevention of hypertension (HT) published by the National High Blood Pressure Education Program Coordinating Committee accepted the role of some dietary factors in a multifactorial approach for the prevention of this disorder. Nonetheless, it also recognized that further research is still needed. Particularly, this statement recommends investigating the role of dietary protein and fiber intake in the prevention of HT (1). So far, the effect of both nutrients in the pathogenesis and prevention of this condition remains elusive.

Recently, two meta-analyses of randomized trials have shown that fiber supplementation can exert a small beneficial effect on blood pressure (BP) levels, particularly among hypertensives 2, 3. But the trials included in both studies assessed short-term interventions (<6 months). Results from well-conducted cohort studies consistently suggest that fiber, especially from cereals, can reduce the risk of coronary heart disease 4, 5, 6, 7, stroke 8, 9 and peripheral arterial disease 10, 11. A possible mechanism to explain this effect could be a reduction in BP values. But prospective studies that have assessed the role of fiber in the incidence of HT are scarce 12, 13, 14, failing on occasion to separate the effect of different types of fiber (15), and they have been conducted exclusively in the U.S.

The study of the relationship between protein intake and BP presents similar problems. Most studies have been cross-sectional, did not discriminate between animal and vegetable protein, or did not adjust for potential dietary confounders 15, 16, 17, 18, 19.

There are no published results from large prospective studies in Mediterranean countries assessing the role of diet on the development of HT. The high consumption of fruit, vegetables, and cereal in these countries, which also implies a higher between-subject variability, makes them an excellent setting to address the role of dietary fiber and protein, particularly vegetable protein, in the prevention of HT.

The objective of our study was to assess the role of different nutritional factors, especially protein and fiber from different sources, on the risk of incident HT in a cohort of Spanish university graduates.

Section snippets

Study Population

The Seguimiento Universidad de Navarra (SUN, University of Navarra) Follow-up Study is a Mediterranean cohort of university graduates. A detailed description of its methods has been published elsewhere (20). Briefly, beginning in December 1999 an explanatory letter and a mailed questionnaire were sent to all former students of the University of Navarra (Spain) and to members of some Spanish professional associations. The follow-up of those who responded to the initial questionnaire is being

Results

We included initially 9,907 participants in the baseline assessment of diet and other risk factors. From these, 1,045 were prevalent cases of HT, 813 reported a history of cardiovascular disease, cancer or diabetes, 1,018 were below or above the limits of caloric intake, and 784 had missing values for one or more potential confounding variable, with some participants included in more than one of these categories. Finally, 6,686 individuals were considered in the initial cohort; 5,880 (88%)

Discussion

In this prospective Mediterranean cohort conducted in Spain, vegetable protein and fiber from cereal were inversely associated with the risk of HT, but only after taking into consideration multiple confounding factors. Fiber from other sources different from cereals and animal protein did not show any association with the incidence of HT. The inverse associations found for vegetable protein and cereal fiber were stronger among men, among older people, and among obese/overweight participants,

Acknowledgments

This study was supported by the Spanish Ministry of Health (Grants PI040233, PI042241, PI050514, and G03/140), the Navarra Regional Government (PI41/2005), and the University of Navarra. Dr. Alvaro Alonso was supported by a Fulbright fellowship and a grant from the MMA Foundation for Medical Research.

We are especially thankful to the SUN participants for their collaboration. We are also indebted to Ms. Carmen de la Fuente for her nutritional advice. Finally, we thank the other members of the

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