Three servings of wholegrains a day 'cuts risk of early death'

"Eating Weetabix for breakfast 'can slash your risk of dying early from any cause'," the Daily Mirror reports.

A new study looking at wholegrain consumption (not just Weetabix) found a strong link between consumption and improved "long-term health and longevity" compared with people who ate little or no wholegrain.

This study pooled data from 14 large studies, which included 786,076 people. It found that the chances of dying from any cause during study follow-up was 16% lower for people who ate the most wholegrain, compared to those who ate the least. The link was strongest when the researchers looked at deaths from heart attacks and strokes. There was a weaker link to a lower risk of dying from cancer.

We can't be sure that all the reduced risk is solely down to eating wholegrain food, as people who eat wholegrain may also have other patterns of healthy behaviour, such as exercising regularly, avoiding smoking and sticking to the recommended guidelines for alcohol consumption.

While some of the studies attempted to account for these types of factors (confounders), it is challenging to filter these influences from analysis.

Nevertheless, this study adds to the evidence that wholegrain foods are an important part of a healthy diet, and should be picked in preference to refined carbohydrates (such as white bread, rice and pasta). Current advice is that healthy starchy food options should make up just over a third of the food we eat. 

Where did the story come from?

The study was carried out by researchers from Harvard TH Chan School of Public Health and Harvard Medical School, and was funded by the National Institutes of Health in the US. The study was published in the peer-reviewed medical journal Circulation.

The Mirror's odd fixation on Weetabix could lead readers to conclude that the study looked only at that brand of breakfast cereal, instead of all types of wholegrain food, including bread, rice, pasta and other types of muesli or cereal. All we can guess is that the photo desk had an image of Weetabix to hand.

The Daily Mail gave a better overview of the study, although the claim that "three slices of wholemeal bread a day slash the risk of dying of heart disease by 25%" is slightly exaggerated. The actual risk reduction for eating 70g a day of wholegrain food, compared to eating no wholegrain food, was 23%.

What kind of research was this?

This was a systematic review that pooled the findings of prospective cohort studies in a meta-analysis to try to better establish whether eating wholegrains is linked with mortality risk.

A meta-analysis is a good way of summarising the results of all studies in a specific area. Prospective cohort studies can help identify links between an exposure and an outcome – in this case, wholegrain food and mortality. But cohort studies can't show whether one factor causes another, usually because other health and lifestyle factors may be involved in the link.

What did the research involve?

Researchers searched literature databases to identify all prospective cohort studies looking at wholegrain intake and mortality. They excluded any studies where it was not possible to estimate wholegrain intake.

They pooled the results, looking separately at death from any cause, death from cardiovascular disease (CVD) and death from cancer.

As well as cohort studies looking specifically at wholegrain, the researchers included data from large surveys of diet and health in the US, known as the National Health and Nutrition Survey (NHANES) which allowed them to include a much bigger data set.

Researchers used the data to calculate the "dose response" to wholegrain, looking at the effect of eating 10g, 50g and 70g of wholegrain a day. One serving (i.e. one slice of bread or bowl of cereal) contains roughly 16g.

Overall, 14 studies met eligibility criteria, most of which (10) were carried out in the US. The studies were conducted between 1971 and 2010 and had follow-up periods ranging from 6 to 28 years.

What were the basic results?

There were 97,867 deaths recorded among the 786,076 people who took part in the studies (so 12.5% of people died).

People who ate the most wholegrain food had a 16% lower chance of dying during the studies, compared to people who ate the least wholegrain food (relative risk [RR] 0.84, 95% confidence interval [CI] 0.8 to 0.88), and had a 18% lower chance of dying from cardiovascular disease (RR 0.82, 95% CI 0.79 to 0.85). They also had a 12% reduced risk of dying from cancer (RR 0.88, 95% CI, 0.83 to 0.94).

An additional serving of wholegrain food each day reduced the risk of dying from any cause by about 7% (RR 0.93, 95% CI 0.92 to 0.94). The researchers calculated that if everyone in these studies had been eating high amounts of wholegrains, this would have reduced the observed mortality rate by about 10%, with similar reductions for cardiovascular and cancer deaths specifically.

How did the researchers interpret the results?

Researchers said the study showed that eating wholegrain food "was inversely associated with mortality in a dose-response manner". In other words, it reduced the chances of death depending on the amount eaten, and that "the association with CVD mortality was particularly strong and robust".

They say this reinforces the current dietary guidelines to eat at least three servings of wholegrain food a day, and to replace refined carbohydrates with wholegrains.

Conclusion

This large, carefully conducted review adds to the evidence we already have that wholegrain food is a healthy part of a balanced diet, and that eating less refined carbohydrates (such as white bread) and more wholegrain alternatives is a good move.

Due to the observational nature of these studies, we cannot be sure that the entirety of the reduced risk of early death is due to eating wholegrains. People who choose wholegrain food may be more likely to live a healthy lifestyle in other ways – for example, they may be less likely to smoke or drink alcohol to excess, and be more likely to exercise.

While the cohort studies adjusted their figures to take account of many confounding factors, we can't be sure they accounted for all of them. The number of confounding factors that each of the studies accounted for varied, but they all took account of smoking.

Most of the studies were carried out in the US, with one from the UK and three from Scandinavia. This means the results may not be applicable to populations with different diets and ethnic backgrounds.

The studies were also conducted over different eras – for example, some looked at the 1970s to 1980s, and others looked at the 00s to 10s. Food availability, dietary patterns and lifestyle may not be directly comparable across different studies. There is also the possibility with all food frequency assessments to inaccurately recall the type and quantity of particular food groups.

Therefore, though the review can't prove that wholegrains were solely responsible for the mortality reduction seen, the evidence that wholegrain food is good for health remains strong, especially for cardiovascular health.