“Going to work on an egg a day?” asks the headline in the Daily Mail today. The article concludes that this “increases the risk of premature death for middle aged men”. The newspaper adds “consumption of seven or more eggs a week pushed up the chances of dying from any cause by 23 per cent”. It says that this latest research could re-open the debate about how many eggs are safe to eat, just when it seemed clear that it was safe to consume them.
The story is based on a study of over 21,000 male doctors in the United States. It warns that the doctors who ate lots of eggs were fatter, more likely to drink alcohol and less likely to exercise. All these factors affect the risk of heart disease, so any advice that more than one egg a day is unsafe would be dubious. A commentator in the same journal says: “Eggs are like all other foods - they are neither ’good‘ nor ’bad‘, and they can be part of an overall heart-healthy diet."
Where did the story come from?
Drs Luc Djoussé and J Michael Gaziano from the Divisions of Aging and Preventive Medicine at the Brigham and Women’s Hospital and Harvard Medical School in Boston carried out this research. The study was supported by grants from the National Cancer Institute and the National Heart, Lung, and Blood Institute in the United States. It was published in The American Journal of Clinical Nutrition , a peer-reviewed medical journal.
What kind of scientific study was this?
This was a prospective cohort study of 21,327 men who took part in the Physicians’ Health Study. This study was a randomised controlled trial which began in 1981. It was designed to test whether low-dose aspirin and beta-carotene, an anti-oxidant supplement, could prevent heart disease, stroke or cancer among US male doctors. Only those aged between 40 and 85 years old were invited to enter the trial. Participants also had to be healthy, without previous illnesses such as stroke, warning stroke, heart attack, ulcers, gout or cancer.
As part of this large study, all participants were asked to give details of how many eggs they ate using a simple, short questionnaire. They were asked to estimate their average egg consumption during the past year five times throughout the study, which ran for over 20 years. Their answers were recorded as: rarely or never, one to two times a month, once a week, two to four times a week, five to six times a week, daily and more than twice a day. They were also asked similar questions about other food groups, including vegetables and breakfast cereals.
The researchers used statistical models to adjust for a number of other factors that could have influenced the results, such as age, sex, smoking and social class. They then analysed the data for links between the number of eggs consumed and ‘cardiovascular outcomes’, heart attacks and stroke, and deaths from any cause, which had been recorded as part of the original trial.
What were the results of the study?
Over the course of the study 1,550 new heart attacks, 1,342 first strokes and 5,169 deaths occurred.
The researchers report that egg consumption was not associated with first heart attack or first stroke in their models. However, in contrast, there was an association with overall mortality: those who ate more eggs were at greater risk.
The highest risk was in the men who ate more than seven eggs a week. They were 23% more likely to die of any cause than those who ate fewer than one. Any small increases in mortality in those men who ate one to six eggs a week were not significant.
What interpretations did the researchers draw from these results?
The researchers conclude that “infrequent egg consumption does not seem to influence the risk of heart disease or stroke in male physicians”. They add that “egg consumption was positively related to mortality”. This means that they had shown a link between increasing egg consumption and increasing chance of death from any cause.
What does the NHS Knowledge Service make of this study?
Several features of this study have been mentioned by the researchers:
- The concern with eggs is that they contain cholesterol. A high dietary intake of eggs may therefore increase the concentration of cholesterol in the blood. However, the researchers acknowledge that they were unable to measure cholesterol, lipids or blood sugar in this study. In fact, it is known that the higher saturated fat content of some foods, such as animal meat, typically raises cholesterol in the blood further than high intakes of cholesterol in the diet.
- They were also unable to adjust for total energy intake as this was not one of the items in the original questionnaire. If they had managed to do either of these things, it would have improved the reliability of these findings.
- The participants in this study were all male doctors. The findings will need to be confirmed in the general population, in women and in certain high-risk groups, such as people with diabetes.
This study has cast some doubt about the exact number of eggs that should be considered safe as part of a healthy diet. It doesn’t, however, provide strong evidence about the risks or benefits of egg consumption. Therefore, it should only be considered in the context of all the other studies which together form the basis of current dietary recommendations.
Sir Muir Gray adds...
The less animal fat the better; both for the individual and the planet.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 10 April 2008
Daily Mirror, 9 April 2008
Links to the science
Am J Clin Nutr 2008; 87:964-969
Cochrane Database Syst Rev 2007, Issue 4