May 21, 2018

expert reaction to eggs and CVD

Among Chinese adults, a moderate level of egg consumption was significantly associated with lower risk of cardiovascular disease, largely independent of other risk factors, report scientists in a study published in the journal Heart.

Prof Nita Forouhi, MRC Epidemiology Unit, University of Cambridge, said:

“One can deliberate on the many limitations and caveats of nutritional research, but the take home message of this research from a large study from China is that at the very least up to 1-egg-a-day is not linked with raised cardiovascular risk, and at best up to 1-egg-a-day may even have health benefits. The researchers accounted for many dietary and other behaviours in their analyses, but it is important to emphasize that eggs are not eaten in isolation, and overall healthy or unhealthy dietary patterns will always matter. This means what you eat with the eggs matters, based on the other research to-date. In a Western context, if you eat eggs with lots of refined white bread, processed meats like bacon and sausages and sugar-rich ketchup, that is materially different to eating an egg with whole-grain bread and vegetables for instance.

“The link between egg consumption and risk of heart disease and stroke has been under scrutiny for decades as eggs were thought to predispose to heart disease due to their high cholesterol content. But increasing research has shown that the correlation between dietary cholesterol and blood cholesterol is modest, when in fact blood cholesterol is more influenced by dietary saturated fat and the body’s own internal processes. Eggs are rich in many healthful nutrients and can be part of a healthy overall diet according to this latest research. This is not a licence to over-indulge in eggs, noting that the researchers were able to examine intakes up to a maximum of 1-egg-per-day in the Chinese population they studied.

“This research like much of nutritional research is observational and not experimental, that is, it follows a large sample of adults over time for health endpoints but does not intervene by prescribing particular diets. We have to largely rely on such research because doing randomised controlled trials of all different foods, unlike for pharmaceutical products, is simply not feasible. Observational research that tries to account for limitations with lots of robustness analyses, as this study has tried to do, can contribute meaningfully to understanding links between diet and health.”

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics at King’s College London, said:

“This very large study of nearly half a million people in China finds that people who ate about 5 eggs a week had an 11 % lower risk of cardiovascular disease (CVD) compared with those who avoided eggs.

“The lower risk was mainly from a reduction in stroke. In China, stroke is more prevalent than coronary heart disease (CHD) and is strongly related to high blood pressure but this study statistically adjusted for raised blood pressure.

“The lower risk of stroke may be due to the increase in protein intake contributed by eggs as previous research in Asia has linked low protein intake to an increased risk of stroke, particularly haemorrhagic stroke.

“But an important limitation of this present study is that the people who consumed eggs regularly were much more affluent than those who avoided them. Indeed, rates of stroke have been falling in Japan, Australia, North America and Europe for several decades for reasons that remain uncertain but may be related to increasing affluence.

“High blood cholesterol is strongly related to increased risk of CHD but not to risk of stroke. Eggs contain cholesterol which contributes to raising blood cholesterol. However, the effect of an intake of 5 eggs/ week would raise cholesterol by 0.1 mmol/L, which conventional wisdom suggests might increase risk of CVD by 1-2%.

“A previous Korean study¹ found that regular egg consumption was associated with coronary artery calcification, which is a strong predictor of future coronary events. Whereas this new study observed that regular egg consumers had a 16% lower risk of major coronary events!

“The evidence presented supports many dietary guidelines for CVD prevention, including those from China, that it is acceptable to eat up to 1 egg a day. This is an important caveat because this study was not able to look at intakes of more than 1 egg/day.”

¹ Choi Y, Chang Y, Lee JE, Chun S, Cho J, Sung E, Suh BS, Rampal S, Zhao D, Zhang Y, Pastor-Barriuso R, Lima JA, Shin H, Ryu S, Guallar E. Egg consumption and coronary artery calcification in asymptomatic men and women. Atherosclerosis. 2015 Aug;241(2):305-12. doi: 10.1016/j.atherosclerosis.2015.05.036.

Dr Gavin Sandercock, Reader in Clinical Physiology (Cardiology) and Director of Research at the University of Essex, said:

“If you study enough people you can find a correlation between almost anything.  To say that eating eggs is good (or bad) for you based on a study like this would be foolish as diet is much more complicated than picking on one foodstuff like eggs.

“In people who rarely ate eggs there were 3.4 deaths per 1000 people compared with 2.2 deaths in people who ate 4-6 eggs a week.  That’s a 0.12% difference in the chance of surviving if you do or don’t eat lots of eggs.** I don’t think that provides very strong evidence that eating eggs is either good or bad for you.

“Taking the findings at face value, this means eating eggs might reduce your risk of heart disease by just 0.1% – whereas being active or quitting smoking reduces this risk by 30-50%.

“Should we all start eating more eggs? Eggs are a good, relatively sustainable source of protein but the complex nature of diet and the myriad other factors that affect heart disease means eating eggs is unlikely to a make any difference to our health.”

**NOTE:

(996.6 survivors [few eggs] / 997.8 survivors [4-6 eggs]) * 100 = 99.88%

100%-99.88% =0.12% difference in chance of surviving

Prof Tim Chico, Professor of Cardiovascular Medicine and Honorary Consultant Cardiologist at the University of Sheffield, said:

“It is very difficult to determine the part any single element of our diet plays in our risk of developing heart disease. This study has shown that people who eat more eggs have lower rates of a range of diseases including heart attack and stroke. It is important to stress that this does not prove that eating eggs protects against these diseases, as there may be other differences between the people eating more eggs that cause these differences.

“This study shows that eating eggs is not associated with higher rates of heart diseases, so people who eat eggs can be reassured that they do not seem to pose a risk to their heart. Although it is important to reduce our risk of heart disease through diet and lifestyle (such as more physical activity), it is unrealistic to think that eating more eggs is going to make much difference unless as part of a more comprehensive shift towards a healthier diet.”

* ‘Associations of egg consumption with cardiovascular disease in a cohort study of 0.5 million Chinese adults’ by Chenxi Qin et al. published in Heart at on Monday 21 May 2018. 

Declared interests

Prof Tom Sanders: I am honorary Nutritional Director of HEART UK

Dr Gavin Sandercock: No conflicts to report

Prof Tim Chico: No conflicts

Prof Nita Forouhi: No conflicts to declare