Cardiovascular disease (CVD) encompasses heart, stroke and blood vessel diseases. Accounting for 34% of all deaths in 2006, it is the leading cause of death in Australia.

There is substantial scientific evidence that wholegrain foods offer protection against cardiovascular disease. In a meta-analysis, Mellen et al (2008) found “a consistent, inverse association between dietary wholegrains and incident cardiovascular disease in epidemiological cohort studies. In light of this evidence, policy makers, scientists and clinicians should re-double efforts to incorporate clear messages on the beneficial effects of wholegrains into public health and clinical practice endeavours.”

Coronary Heart Disease (CHD):

The evidence for the role of wholegrains in reducing coronary heart disease risk is compelling – it shows increasing wholegrains to 2-4 serves a day can reduce the risk of heart disease by as much as 40% – equal to the effect of statin drugs.

In 2006 Food Standards Australia New Zealand (FSANZ) commissioned a review of a potential high-level health claim for wholegrains and CHD. That review concluded that the large body of prospective data provides convincing evidence for a protective effect of wholegrains against CHD. However, FSANZ did not accept that the relationship was convincing enough because of inconsistency in the definitions of wholegrain used in the studies, and because most studies focused on oats and barley, rather than wheat, which is the predominant cereal consumed in Australia.

More recent reviews have been strongly consistent in supporting the protective effect of wholegrains. There have now been four meta-analyses and at least four systematic reviews published in international peer-reviewed journals which all report an association of reduced risk of CHD with wholegrain food consumption. The most recent systematic review published in 2008 concluded three serves of wholegrains a day is associated with a 30-48% risk reduction. Seven of the nine cohort studies summarised in that review found there was a significant reduction in relative risk with intakes as low as only one serve of wholegrains a day.

The definition of wholegrain foods in these studies varied from requiring 25% to 51% wholegrain ingredients. Using the few studies employing the stricter US Food and Drug Administration (FDA) definition of 51%, De Moura (2008) concluded the body of evidence was insufficient to draw conclusions. However, most epidemiological studies, such as the Iowa Women’s Health Study, the Physicians Health Study and the Nurses Health Study used the lower 25% definition, and reported a positive association, suggesting the protective effect would also be present for foods with a higher percentage of wholegrains.

Another systematic review of prospective cohort studies and randomised controlled trials investigating the strength of causal evidence for a range of dietary factors in relation to CHD found moderate evidence of causal association for wholegrains – the same level of evidence as found for fish, fruit and folate.

Stroke:

Few studies exist that specifically examine the relationship between wholegrain intakes and risk of stroke. However, one notable study examined the relationship of wholegrain intake and risk of ischaemic stroke in a 12-year follow-up of the Nurses Health Study, which included over 75,500 women. An inverse association was observed between wholegrain intake and ischaemic stroke risk, with the relative risk for ischaemic stroke in the highest quintile (median intake 2.7 servings/day) being 0.69 (95% CI, 0.50–0.98, P=0.04 for trend) relative to the lowest quintile (median intake 0.13 servings/day). No such inverse relationship was observed for refined grain intake.

Mixed results with other studies have been shown when adjustment has been made for potential confounders. However, the trends overall are strongly suggestive of a protective effect of wholegrain on risk of stroke.

Hypertension:

Three prospective cohort studies have reported an inverse association between wholegrain consumption and hypertension. The US Health Professionals Follow-Up Study followed 31,864 male participants without hypertension for 18 years. It found that for those in the highest quintile of wholegrain intake (46g a day) the incidence of hypertension was reduced by 19% compared to those with the lowest intake (3g a day), independent of sodium intake. Total bran intake was also inversely associated, with a 15% risk reduction in the highest versus lowest quintiles of intake.

In another prospective cohort of 28,926 female health professionals followed for 10 years, those who consumed 0.5-1, 1-2, 2-4 and 4 wholegrain servings a day had multivariate relative risks for hypertension of 0.93, 0.93,0.92, and 0.77 respectively, compared with those who consumed <0.5 wholegrain servings a day.

In the CARDIA study, the hazard ratio for incidence of hypertension during 15 years of follow-up in 4,304 young adults was 0.83, with a wholegrain intake of >1.9 serves a day.

In addition, three randomised controlled trials have examined the effect of wholegrain cereal supplementation. These studies found:

• • two serves of oats a day led to greater reduction in medication than two serves of wheat cereal in 43 patients on hypertensive medication;
• • three serves of foods supplemented with oat -glucan significantly reduced blood pressure in hypertensive subjects who were obese, but not others;
• • replacement of white rice with brown rice, white bread with wholegrain bread, and low-fibre cereals with barley or whole wheat cereals led to significant reduction in systolic and diastolic blood pressure during a five week period, in 25 overweight hypercholesterolaemic patients.

The suggested mechanisms by which wholegrains can reduce blood pressure include increased insulin sensitivity, prevention of weight gain and improved endothelial function.

Blood Lipids:

A 2007 Cochrane Review of randomised trials assessed the evidence for the relationship between consumption of wholegrain foods and the effect on risk factors for CHD. Ten trials met the inclusion criteria and in eight of these studies, the wholegrain component was oats. Seven of these eight studies reported lower total cholesterol and LDL cholesterol with oatmeal foods compared to the control foods, with a significant weighted mean difference of -0.19mmol of total cholesterol/L.

Significant reductions in blood lipids have been demonstrated not only with oats, but also barley and psyllium, and since 1997 the US FDA has permitted a health claim for cereal foods containing at least 0.75g of soluble fibre a serve. A cross-sectional study reported that intakes of wholegrains (but not refined grains) and cereal fibre were inversely associated with total and LDL cholesterol levels among participants from the Baltimore Longitudinal Study on Aging.

Suggested Mechanisms:

Soluble Fibre: A major mechanism by which wholegrain foods affect cardiovascular disease risk is through the action of viscous soluble fibres, including beta-glucan and soluble pentosans, which slow digestion and increase cholesterol excretion. Such fibres can inhibit cholesterol absorption by as much as 20% and promote the excretion of bile by up to 144%.

Nutrients and Phytochemicals: While soluble fibre is an important mechanism it is not the only one. It has been clearly demonstrated that wheat fibre does not reduce serum cholesterol levels, but in a randomised crossover study published in 2010, consumption of wholemeal wheat foods for three weeks significantly decreased fasting plasma cholesterol and LDL cholesterol levels in healthy individuals. This suggests that components other than the fibre in wholegrain foods may also have an effect on cardiovascular risk.

Wholegrains, particularly rye, contain phytoestrogens known as ligans. Compared to white wheat bread, eating wholemeal rye bread at least doubles the levels of ligans in the blood and urine in the form of a chemical called enterolactone. A study that assessed heart disease risk factors showed significant associations between raised serum enterolactone concentration and reduced risk of death due to coronary heart disease and cardiovascular disease. (GGHN – do you have a reference for this? I’ve taken this from the existing website: ‘Cereal Grains and Coronary Heart Disease’ page)

Other components of wholegrains which have been suggested to be important include magnesium, folate, alpha-tocotrienol and the variety of phytochemicals which may directly or indirectly inhibit oxidative stress and inflammation.

Antioxidants: Grain-specific antioxidants exist, such as oryzonol in rice, avenanthramides in oats and ferulic acid in corn and wheat. Some of these phenolics have anti-atherogenic activity.

Certain other antioxidants found in grains like vitamin E and its isomers (tocopherols and tocotrienols), selenium and polyphenols may also bestow cardio-protective benefits. GGHN – I added ‘antioxidants’ in this section. Please check you are happy with this.

Gluten: Grain proteins such as gluten, with a low lysine to arginine ratio, may help to reduce the risk of developing atherosclerosis through its effect on nitric oxide production.

To view references click here