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15 November 2012
Regular egg consumption: a hidden residual risk factor to be considered in high-risk patients

New data show that egg yolk consumption is a significant predictor of atherosclerotic burden, more so than total cholesterol. These findings merit further study in a hard outcomes trial testing the hypothesis that egg yolk consumption should be reduced or avoided in high-risk individuals.

Spence JD, Jenkins DJA, Davignon J. Egg yolk consumption and carotid plaque. Atherosclerosis 2012;224:469-73.
Summary
Comments & References
STUDY SUMMARY
Objectives To investigate whether carotid plaque burden is influenced by egg yolk consumption
Study design Prospective study
Study population 1,262 consecutive patients (mean age 61.5 years, 47% women, 13% with diabetes) referred to vascular prevention clinics at an University Hospital London, Ontario, Canada  
Primary variable Carotid total plaque area (TPA)
Methods
  • Carotid TPA was measured as previously described.1 Data were normalised by multiple linear regression analysis and adjusted for age
  • Egg yolk consumption and smoking were investigated as predictors of TPA.
    • Egg yolk consumption was assessed by lifestyle questionnaire and categorised by quintiles of egg yolk years, defined as the number of eggs per week x the number of years consumed; <50, 50-110, 110-150, 150-200 and ³200
    • Smoking exposure was assessed by lifestyle questionnaire and categorised into roughly equal groups that made clinical sense: 0 pack years (39.9%), <10, 10-20, 20-40 and >40 pack years
Main results
  • Carotid TPA increased exponentially with egg-yolk years (Figure 1).

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Figure 1. Carotid plaque area increases exponentially with increasing quintiles of egg yolk consumption.
From Spence JD et al (2012).

  • Patients who ate £2 eggs/week had significantly less carotid plaque than those who ate 3 or more eggs per week (125 ±130 mm2 versus 132 ± 142 mm2, p<0.0001 after adjustment for age).
  • Egg yolks years was a significant predictor of baseline TPA, even after adjustment for sex, total cholesterol, systolic blood pressure, diabetes, body mass index and pack-years of smoking.
  • Egg yolk years was a better predictor of baseline TPA than fasting cholesterol or BMI.
  • In contrast, triglycerides, HDL cholesterol and LDL cholesterol were not significantly predictive of baseline TPA.
  • Smoking was also associated with exponentially increased TPA.
Author's conclusion

Regular consumption of egg yolk should be avoided by people at risk of cardiovascular disease.

 

COMMENT

This study shows a strong association between egg yolk consumption and carotid plaque burden. Indeed, the magnitude of the effect is generally similar to that seen with smoking (not shown here); the effect on plaque burden associated with the upper quintile of egg yolk consumption was about 70% of that seen in the upper smoking quintile, i.e. corresponding to at least 40 pack-years exposure. The effect on the arteries of egg yolks and smoking appears to be additive (in press, Atherosclerosis).
Dietary cholesterol, as found in egg yolks, not only raises LDL cholesterol levels, but also increases the susceptibility of LDL to oxidation; concomitant effects of vascular inflammation and oxidative stress contribute to endothelial dysfunction.(2) Furthermore, the effects of egg yolk consumption on postprandial lipaemia are relevant in the context of residual cardiovascular risk, in reducing postprandial clearance of atherogenic chylomicron remnants by about 50%.(3)


Emerging evidence also suggests that interaction between dietary phosphatidylcholine (otherwise referred to as lecithin), which is found in eggs, and the gut flora may be relevant. The gut flora or microbiota play an intermediate metabolic role in converting choline, released by hydrolysis of phosphatidylcholine, to trimethylamine, which then undergoes oxidation in the liver. Studies in animal models have shown an association between dietary choline, plasma levels of oxidative metabolites of trimethylamine, and plaque development.(4) Thus, these mechanistic data provide further support for a deleterious association between egg yolk consumption and atherosclerotic plaque development.


In conclusion, the findings from this study suggest that reducing or avoiding egg yolk consumption may be another, emerging and relevant therapeutic lifestyle change to reducing residual cardiovascular risk in the high-risk patient. These data warrant testing in a prospective randomized outcomes trial.

References

1. Spence JD, Eliasziw W, DiCiccoM et al. Carotid plaque area: a tool for targeting and evaluating vascular preventive therapy. Stroke 2002;33:2916-22.
2. Spence JD, Jenkins DJA, Davignon J. Dietary cholesterol and egg yolks: Not for patients at risk of vascular disease. Can J Cardiol 2010;26:e336-9.
3. Cesar TB, Oliveira MR, Mesquita CH, Maranhao RC. High cholesterol intake modifies chylomicron metabolism in normolipidemic young men. J Nutr 2006;136:971-6.
4. Wang Z, Klipfell E, Bennett BJ et al. Gut flora metabolism