Could an egg a day help keep stroke at bay?

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An egg in the pan: a US meta-analysis drew on data from existing cohort studies exploring links between egg consumption and the risks of heart disease and stroke.
An egg in the pan: a US meta-analysis drew on data from existing cohort studies exploring links between egg consumption and the risks of heart disease and stroke.
Matthew Murdoch, Flickr CC
A systematic review and meta-analysis by US researchers of existing data collected from around 300,000 people across an array of studies suggests that eating up to one egg a day may cut a person’s risk of suffering a fatal stroke, though not of developing heart disease.

For years, scientists have debated the effects of egg consumption on human health. Because eggs contain high levels of cholesterol, they have been assumed by many to increase people’s risk of developing coronary heart disease (CHD) by raising their cholesterol levels.

More recent studies, however, show that the presence of cholesterol in food products has minimal impact on levels of cholesterol in the bloodstreams of those routinely consuming such foods. In fact, it appears that most of the cholesterol circulating in a person’s blood is made by that person’s liver.

The meta-analysis

The study, conducted by researchers from Michigan’s EpidStat Institute and DLW Consulting Services in Utah, was funded by the US’s Egg Nutrition Center (arguably, raising potential conflicts of interest) and published in the Journal of the American College of Nutrition in late 2016.

The ENC, which refers to itself as the “science and nutrition education division” of the American Egg Board (AEB), http://www.aeb.org is a trade association representing American egg farmers.

The idea was to undertake a review and up-to-date analysis of existing evidence on the link between eating eggs and the risks of stroke and CHD.

The EpidStat-DLW research team identified all prospective studies published up to August 2015 that looked at adults’ egg consumption and either heart disease or stroke. All were prospective cohort studies, which can determine associations between factors but not the direction of causation.

The team pooled the results of these studies, then analysed the pooled data in an attempt to ascertain whether higher egg consumption had any impact on stroke and/or CHD outcomes.

They also looked for what is known as a ‘dose response’ – that is, any indication that a person’s risk of developing CHD or suffering a stroke rose or fell in line with the number of eggs that person ate in an average week.

Most of the studies upon which the analysis was conducted had classified ‘high egg consumption’ as around an egg per day and ‘low egg consumption’ as less than two eggs a week.

Most, but not all the studies had adjusted their data to account for confounding factors that could have affected subjects’ risk of heart disease and stroke, such as age, gender, weight, exercise levels and regularity, smoking history – and, in a few of the studies, the ‘healthiness’ or otherwise of participants' diets overall.

The researchers also conducted standard tests to check for publication bias and to determine whether their summary findings had been unduly affected by one or more of the studies from which data was drawn.

Brown eggs: the meta-analysis suggested that eating an egg a day, or thereabouts, could lessen a person's risk of stroke by 12 percent.
Stock up on these babies: the meta-analysis suggested that eating an egg a day, or thereabouts, could lessen a person's risk of stroke by 12 percent.
Kevin Choi, Flickr CC

Key findings

The EpidStat-DLW meta-analysis revealed no significant association between egg consumption and heart disease but a 12 percent reduction in the risk of suffering a stroke in those who ate an egg every day or so, compared to people who ate less than two eggs a week.

Based on their analysis of data from seven studies, collected from a total of 276,000 people, the researchers concluded that those whose egg consumption was categorised as ‘high’ (about an egg a day) were no more or less likely to develop heart disease than those whose egg consumption was deemed ‘low’ (less than two eggs a week).

Analyses of data from seven studies including 308,000 people suggested that those who ate an egg or thereabouts per day were 12 percent less likely to suffer a stroke than those who consumed less than two eggs a week.

The researchers found no indications of ‘dose response’, however – a person’s risk of stroke risk did not appear to diminish (or increase) as their weekly egg consumption rose.

“Consumption of up to one egg daily may contribute to a decreased risk of total stroke [all types of stroke] and daily egg intake does not appear to be associated with risk of coronary heart disease,” the team concluded.

Cracked egg: the study pooled data from existing studies that looked at egg consumption and CHD or stroke and analysed it for possible associations.
The study pooled data from existing studies that looked at egg consumption and CHD or stroke and analysed it for possible associations.
Daniel Novta, Flickr CC

Implications – and shortcomings

The review and meta-analysis supports the contention that eggs can be a regular part of a healthy diet, without increasing your risk of heart disease or stroke. Indeed, eating eggs regularly could be a means of lowering your risk of suffering the latter.

That said, however, its findings should be interpreted with some caution, as the data the study drew on included little information on people's overall dietary intake; nor did the researchers have access to information on how eggs were prepared that may have been relevant to risks of stroke and CVD.

The EpidStat-DLW researchers did not find a statistically significant association between a person’s consumption of eggs and their risk of fatal stroke. Nor did the meta-analysis unearth evidence that ‘eating more eggs was better’– a person’s risk of stroke did not appear to diminish in line with the number of eggs that person ate per week.

The conclusion

Don’t assume that eating ‘your daily egg’ religiously gives you license to fry that egg in butter and add high-fat bacon, hash browns and the like –12 percent is a small risk reduction, especially given the study’s limitations.

As eggs are a great source of protein, vitamins and minerals, however, adding a poached or boiled one, most days, to breakfast (or lunch, or dinner) is a healthy way to fuel your day, won’t up your risk of CHD and, combined with a healthy lifestyle, may even help keep stroke at bay.

Further reading

Read more about preventing strokes from:

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