Whole grain intake and cardiovascular disease: A meta-analysis

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Abstract

Background and aims

Whole grain food sources have been associated with lowered risk of cardiovascular disease (CVD). Studies in recent years have strengthened this observation and elucidated potential mechanisms for this association. This study sought to quantitate the available observational evidence on whole grain intake and clinical cardiovascular events.

Methods and results

Seven prospective cohort studies with quantitative measures of dietary whole grains and clinical cardiovascular outcomes were identified from MEDLINE searches and a review of the literature. Based on event estimates adjusted for cardiovascular risk factors, greater whole grain intake (pooled average 2.5 servings/d vs. 0.2 servings/d) was associated with a 21% lower risk of CVD events [OR 0.79 (95% CI: 0.73–0.85)]. Similar estimates were noted for different CVD outcomes (heart disease, stroke, fatal CVD) and in sex-specific analyses. Conversely, refined grain intake was not associated with incident CVD events [1.07 (0.94–1.22)].

Conclusions

There is a consistent, inverse association between dietary whole grains and incident cardiovascular disease in epidemiological cohort studies. In light of this evidence, policy-makers, scientists, and clinicians should redouble efforts to incorporate clear messages on the beneficial effects of whole grains into public health and clinical practice endeavors.

Introduction

Cardiovascular disease (CVD) accounts for one-third of deaths worldwide, and the World Health Organization estimates that, over the next two decades, developing countries will bear the brunt of the increasing burden of CVD [1]. Over thirty years ago, Dr. Trowell noted that sub-Saharan Africa had a lower prevalence of ischemic heart disease than industrialized European and American populations, hypothesizing that observed differences were attributable to the relative intake of refined versus whole plant food sources [2]. This came to be known as the “fiber hypothesis”, which related fiber intake from cereal and plant sources to chronic heart and gastrointestinal diseases. The first prospective evaluation of the “fiber hypothesis” with respect to heart disease came from the United Kingdom [3]. Morris et al. found that cereal fiber (but not vegetable fiber) was negatively associated with incident ischemic heart disease. The first study to prospectively associate whole grain consumption with cardiovascular events was the Seventh Day Adventists' study, in which individuals who consumed wheat bread had a 55% lower risk of non-fatal MI than those who ate white bread [4]. In 2003, Dr. Anderson synthesized data from thirteen studies evaluating intake of whole grains, fruits, vegetables, and fiber with respect to risk for clinical cardiovascular disease [5]. Of five studies prospectively evaluating whole grain intake and cardiovascular risk, higher intake of whole grains was associated with a 29% lower risk for cardiovascular events (adjusted RR 0.71, 95% CI 0.48–0.94). However, since this analysis, multiple observational studies have replicated this association and important causal pathways have been elucidated, including effects on glucose homeostasis, serum lipids, and endothelial function. We sought to quantitate the available observational evidence on whole grain intake and clinical cardiovascular events and review the potential mechanisms of this association.

Section snippets

Methods

We identified observational studies that evaluated the association between whole grain intake and clinical cardiovascular events using the following inclusion criteria: 1. the studies were performed using self-reported quantitative measures of whole grain intake (e.g. servings/day); 2. cardiovascular events were ascertained prospectively; and 3. the studies provided adequate data to generate adjusted event rates. Studies were identified from a MEDLINE search for ‘whole grain’ and

Results

Six studies provided information for demographic-adjusted analyses [10], [11], [12], [13], [14], [15], and seven included information for risk-factor-adjusted analyses [10], [11], [12], [13], [14], [15], [16] (Table 2). Among these cohorts, the pooled average intake of those with high intake was 2.5 servings/d, while consumption in the comparison group averaged 0.2 servings/day. High intake of whole grains was associated with a 37% lower risk of incident cardiovascular disease in the analyses

Discussion

The inverse association between whole grain intake and cardiovascular disease has been consistently demonstrated in multiple observational studies. In analyses reflecting cardiovascular events from over 149,000 participants, we found that consumption of 2.5 servings of whole grains was associated with a 21% lower risk of incident CVD compared to intake of 0.2 servings per day, after adjustment for cardiovascular risk factors. Similarly, whole grain intake is inversely associated with

Whole grain intake and CVD risk: potential mechanisms

Grains consist of bran, germ, and endosperm components. When refined, the carbohydrate-rich endosperm component is retained, while many biologically active agents, such as fiber, vitamins, minerals, antioxidants, and other plant compounds (lignans, phytosterols, etc.) are removed with the bran and germ [19]. These biological agents influence cardiovascular risk through effects on glucose homeostasis [20], [21], lipids and lipoproteins [16], [22], endothelial function [23], and other mechanisms

Conclusions

Despite the abundant evidence in support of increasing whole grain intake and a diverse assortment of whole grain food sources (Table 3), intake remains low. Data from the National Health and Nutrition Examination Survey 1999–2000 found that only 8% of U.S. adults consume three or more servings of whole grain per day, with most whole grains consumed in snack foods (41%) [followed by cereals (32%), breads (18%) and other sources (9%)] [53]. The same data revealed that 42% of adults eat no whole

Acknowledgment

PBM was sponsored by an NIH training grant (T32 HL76132).

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