Eggs don’t give you heart attacks and strokes, conclude nutritional scientists at Huazhong University of Science and Technology in China. They did a meta-study in which they collected existing data on half a million people and reanalysed it.
After scientists determined that an egg yolk contains 150-180 mg cholesterol, nutritionists advised against eating eggs. So much cholesterol was bad for the heart and blood vessels, was the message. Sensible people would confine their egg eating to 2-3 eggs a week, and no more.
Studies were done that backed up this advice. The more eggs people eat, the higher the levels of bad cholesterol [LDL] in their blood, studies showed. From these studies [Am J Clin Nutr. 2001 May;73(5):885-91.] it was possible to calculate that for every whole egg per day that you eat (cholesterol is only present in the yolk) you raise your chance of having a heart attack by 2.1 percent.
Now 2.1 percent isn’t so high, and a calculation is not scientific proof. And it looked for a while as though that proof would never be delivered. Meanwhile the arrival of statins and blood pressure reducing drugs brought interest in nutrition and cardiovascular disease down to nil in rich countries, and scientific research on the relationship between diet and cardiovascular disease ground to a halt.
In up and coming economies such as China and India the situation is different. As the food industry grows it has started to destroy traditional eating habits and the number of people suffering heart attacks and strokes is growing. These countries do not yet have enough money for mass provision of medicines, so scientists are once again starting to look at the relationship between diet and cardiovascular disease there.
The Chinese researchers are no exception. They decided to collect all available epidemiological studies on the relationship between the consumption of eggs and the chance of developing cardiovascular disease. They then aggregated the data in these studies and reanalysed it.
The researchers found 17 studies that met with their approval, and these contained data on 474,342 people. Some of the studies concerned heart attacks [first figure below], others concerned strokes [second figure below].
As you can see above, eggs slightly reduce the chance of having a stroke.
The Chinese discovered, however, that among diabetics a high intake of whole eggs does increase the risk of heart attack. Click on the summary table below to access the full information.
“Results from our meta-analysis do not support that higher egg consumption is associated with elevated risk of coronary heart disease and stroke”, the researchers summarise their findings. “Subgroup analyses suggest a positive association between higher egg intake and risk of coronary heart disease in diabetic patients, and an inverse association between higher egg consumption and incidence of hemorrhagic stroke. Studies with larger sample sizes and longer follow-up times are warranted to confirm these subgroup results.”
Egg consumption and risk of coronary heart disease and stroke: dose-response meta-analysis of prospective cohort studies.
Rong Y, Chen L, Zhu T, Song Y, Yu M, Shan Z, Sands A, Hu FB, Liu L.
Department of Nutrition and Food Hygiene, Hubei Key Laboratory of Food Nutrition and Safety, Tongji Medical College, Huazhong University of Science and Technology, 430030 Wuhan, PR China.
To investigate and quantify the potential dose-response association between egg consumption and risk of coronary heart disease and stroke.
Dose-response meta-analysis of prospective cohort studies.
PubMed and Embase prior to June 2012 and references of relevant original papers and review articles. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Prospective cohort studies with relative risks and 95% confidence intervals of coronary heart disease or stroke for three or more categories of egg consumption.
Eight articles with 17 reports (nine for coronary heart disease, eight for stroke) were eligible for inclusion in the meta-analysis (3,081,269 person years and 5847 incident cases for coronary heart disease, and 4,148,095 person years and 7579 incident cases for stroke). No evidence of a curve linear association was seen between egg consumption and risk of coronary heart disease or stroke (P=0.67 and P=0.27 for non-linearity, respectively). The summary relative risk of coronary heart disease for an increase of one egg consumed per day was 0.99 (95% confidence interval 0.85 to 1.15; P=0.88 for linear trend) without heterogeneity among studies (P=0.97, I(2)=0%). For stroke, the combined relative risk for an increase of one egg consumed per day was 0.91 (0.81 to 1.02; P=0.10 for linear trend) without heterogeneity among studies (P=0.46, I(2)=0%). In a subgroup analysis of diabetic populations, the relative risk of coronary heart disease comparing the highest with the lowest egg consumption was 1.54 (1.14 to 2.09; P=0.01). In addition, people with higher egg consumption had a 25% (0.57 to 0.99; P=0.04) lower risk of developing hemorrhagic stroke.
Higher consumption of eggs (up to one egg per day) is not associated with increased risk of coronary heart disease or stroke. The increased risk of coronary heart disease among diabetic patients and reduced risk of hemorrhagic stroke associated with higher egg consumption in subgroup analyses warrant further studies.
PMID: 23295181 [PubMed – in process] PMCID: PMC3538567