Associations of Dietary Cholesterol and Egg Consumption with Incident Cardiovascular Disease and Total Mortality

Associations of Dietary Cholesterol and Egg Consumption with Incident Cardiovascular Disease and Total Mortality

Associations of Dietary Cholesterol and Egg Consumption with Incident Cardiovascular Disease and Total Mortality

 

By Kevin C. Maki, PhD and Heather Nelson Cortes, PhD

 

Despite decades of research, the association between dietary cholesterol consumption, cardiovascular disease (CVD) and mortality remains controversial.  Adding to this controversy are the confusing recommendations in the 2015-2020 Dietary Guidelines for Americans.1,2  The Guidelines state that cholesterol is not a nutrient of concern for overconsumption, but also recommend that individuals should consume as little dietary cholesterol as possible while following a healthy eating pattern.  A meta-analysis of prospective cohort studies published in 2015 did not show statistically significant associations between dietary cholesterol consumption and incident CVD, coronary artery disease or stroke, although higher dietary cholesterol intake was associated with an increased level of low-density-lipoprotein cholesterol (LDL-C).3  Because a large chicken egg (~50 g) contains roughly 186 mg of cholesterol,4 limiting egg consumption has been recommended as a way to decrease dietary cholesterol and to possibly reduce the risk of CVD.

 

Zhong et al. recently published an analysis of the associations between intakes of dietary cholesterol and eggs with incident CVD and total mortality from the Lifetime Risk Pooling Project.5  The Lifetime Risk Pooling Project contains data from 6 cohorts in which usual dietary intake, fatal and nonfatal coronary heart disease, stroke, heart failure and CVD from other causes were assessed. The 6 cohorts were the Atherosclerosis Risk in Communities (ARIC) Study,6 Coronary Artery Risk Development in Young Adults (CARDIA) Study,7 Framingham Heart Study (FHS),8  Framingham Offspring Study (FOS),9 Jackson Heart Study (JHS)10 and the Multi-Ethnic Study of Atherosclerosis (MESA).11  The analysis included 29,615 participants (mean [standard deviation] age at baseline, 51.6 [13.5] years).5  There were 13,299 (44.9%) men and 9,204 (31.1%) subjects were black.  The median follow-up was 17.5 years (interquartile limits, 13.0-21.7; maximum, 31.3) during which there were 5,400 incident CVD events and 6,132 all-cause deaths. 

 

Dietary cholesterol and egg consumption showed linear associations with incident CVD and all-cause mortality (all P values for nonlinear terms, 0.19-0.83).  The addition of each 300 mg of dietary cholesterol per day was associated with higher risk of incident CVD (adjusted hazard ratio [HR] 1.17, 95% confidence interval [CI], 1.09-1.26 and adjusted absolute risk difference [ARD] 3.24%, 95% CI 1.39%-5.08%).  The same increment of dietary cholesterol per day was also associated with higher risk of all-cause mortality (adjusted HR 1.18, 95% CI 1.10-1.26 and adjusted ARD 4.43%, 95% CI 2.51%-6.36%). Consumption of each additional half egg per day was associated with higher risk of incident CVD:  adjusted HR 1.06, 95% CI 1.03-1.10; adjusted ARD 1.11%, 95% CI 0.32%-1.89% and all-cause mortality:  adjusted HR 1.08, 95% CI 1.04-1.11; adjusted ARD 1.93%, 95% CI 1.10%-2.76%.

 

The associations between egg consumption and incident CVD (adjusted HR 0.99, 95% CI 0.93-1.05) and all-cause mortality (adjusted HR 1.03, 95% CI 0.97-1.09) were no longer significant after adjusting for dietary cholesterol consumption.  The associations between dietary cholesterol intake and incident CVD, as well as mortality, remained statistically significant after adjusting for traditional CVD risk factors (including non-high-density lipoprotein cholesterol [non-HDL-C] concentration), various nutrient intakes and measures of diet quality.

 

Comment.  This new analysis by Zhong et al. has several strengths, including a long follow-up period and the availability and analysis of a great deal of dietary information, such as indices of diet quality, including the Alternative Healthy Eating Index, a Dietary Approaches to Stop Hypertension score and a Mediterranean Diet index.  The supplemental material for the paper includes extensive information from sensitivity analyses.

 

Despite these strengths, the results are difficult to interpret, in our view, for several reasons.  First, adjustment for non-HDL-C level did not materially alter the association between dietary cholesterol intake and incident CVD.  This is curious because the presumed mechanistic link between dietary cholesterol intake and incident CVD is through the effect of dietary cholesterol to raise the circulating concentrations of LDL-C and non-HDL-C, which are well-established major CVD risk factors that are believed to be causally related to CVD incidence.  In a communication with the authors, we were told that adjustment for non-HDL-C and HDL-C levels had virtually no impact on the point estimates for CVD risk.  Data were missing for LDL-C for 900 subjects, so this was not assessed separately.  Given the lack of effect of adjustment for lipid levels, if the association between dietary cholesterol intake and CVD risk is causal, one must hypothesize mechanisms other than the effect of dietary cholesterol to raise atherogenic cholesterol (LDL-C and non-HDL-C) levels.

 

A second issue is that within the range of typical cholesterol intakes in the United States (<300 mg/d), no significant increases in risk for incident CVD or all-cause mortality were observed.  For example, for intakes of 200 to <300 mg/d compared to <100 mg/d, the HR for CVD in model 3 (adjusted for CVD risk factors and medication use) was 0.99, 95% CI 0.87-1.12 and for mortality was 0.95, 95% CI 0.84-1.06.  Therefore, the traditional recommendation to limit dietary cholesterol intake to <300 mg/d is supported by these analyses.

 

Finally, the relationship between cholesterol intake and non-CVD mortality is similar to that for all-cause mortality, with model 3 HR for all-cause mortality of 1.15 (95% CI 1.07-1.23) compared with 1.13 (95% CI 1.04-1.22) for non-CVD mortality (eFigure 5 in the supplemental material).  We are not aware of biologically plausible mechanisms that would explain an increase in non-CVD mortality as a consequence of higher dietary cholesterol intake.  Therefore, the possibility of residual confounding must be considered.

 

It is also notable that two other recent publications have reported on the association between egg consumption and incident CVD.  In the EPIC-Norfolk cohort,12 the top quintile of egg consumption (median 40 g/d) was associated with a non-significantly lower adjusted incidence of ischemic heart disease compared with the lowest quintile (HR 0.93, 95% CI 0.86-1.01), with a p-value for trend across quintiles of 0.37.  Also, in a large study in China with nearly 500,000 participants,13 those who consumed eggs daily had lower risks for incident CVD (HR 0.89, 95% CI 0.87-0.92) and ischemic heart disease (HR 0.88, 95% CI 0.84-0.93) than those who rarely or never consumed eggs, with significant inverse trends (p < 0.001) over the range of egg intake categories.  So, within the space of one year we have seen publications from observational studies reporting associations ranging from a significant inverse association, to no significant relationship, to a significant positive association of egg intake with incident CVD and/or ischemic heart disease.

 

Our view is that the available data show convincingly that higher dietary cholesterol intake modestly raises the level of LDL-C, a major CVD risk factor, with linear models indicating a rise of ~2 mg/dL of LDL-C for each increment of 100 mg/d of dietary cholesterol.3,14,15  The results from the Zhong et al. study do not suggest elevations in CVD incidence or mortality risk for intakes of dietary cholesterol below the traditional recommendation of <300 mg/d (i.e., for intake of 200-299 mg/d compared with <100 mg/d).5  Their results also showed that the relationship between egg consumption and CVD and mortality risk could be accounted for by the cholesterol content of eggs.  Therefore, we believe it is reasonable to suggest that whole eggs can be a part of a healthy dietary pattern, provided that total dietary cholesterol intake is not excessive, with the traditional recommendation being not to exceed 300 mg/d.  For those with hypercholesterolemia, it may be reasonable to further restrict dietary cholesterol intake.  The National Lipid Association recommendations for management of dyslipidemia suggest that dietary cholesterol be limited to <200 mg/d for those with hypercholesterolemia, and further restriction may be prudent for those who are known to be hyperresponders, i.e., those who have a larger than average increase in LDL-C in response to an increase in dietary cholesterol.16  Additional research will be needed to determine whether a dietary cholesterol intake >300 mg/d is causally related to adverse health outcomes, and, if so, what mechanisms account for these relationships.

 

References

  1. US Department of Health and Human Services and US Department of Agriculture. 2015-2020 Dietary Guidelines for Americans. 8th Edition. December 2015. https://health.gov/dietary guidelines/2015/guidelines/.
  2. Dietary Guidelines Advisory Committee. Scientific Report of the 2015 Dietary Guidelines Advisory Committee: Advisory Report to the Secretary of Health and Human Services and the Secretary of Agriculture. Washington, DC: US Dept of Agriculture, Agricultural Research Service; 2015.
  3. Berger S, Raman G, Vishwanathan R, et al. Dietary cholesterol and cardiovascular disease. Am J Clin Nutr. 2015;102:276-294.
  4. US Department of Agriculture. Agricultural Research Service, Nutrient Data Laboratory. USDA National Nutrient Database for Standard Reference, Release 28. Version Current: September 2015. https://ndb.nal.usda.gov/ndb/.
  5. Zhong VW, Van Horn L, Cornelis MC, et al. Associations of dietary cholesterol or egg consumption with incident cardiovascular disease and mortality. JAMA. 2019;321:1081-1095.
  6. The ARIC Investigators. The Atherosclerosis Risk in Communities (ARIC) study: design and objectives. Am J Epidemiol. 1989;129:687-702.
  7. Friedman GD, Cutter GR, Donahue RP, et al. CARDIA: study design, recruitment, and some characteristics of the examined subjects. J Clin Epidemiol. 1988;41:1105-1116.
  8. Wong ND, Levy D. Legacy of the Framingham Heart Study: rationale, design, initial findings, and implications. Glob Heart. 2013;8:3-9.
  9. Feinleib M, Kannel WB, Garrison RJ, et al. The Framingham Offspring Study: design and preliminary data. Prev Med. 1975;4:518-525.
  10. Taylor HA Jr, Wilson JG, Jones DW, et al. Toward resolution of cardiovascular health disparities in African Americans. Ethn Dis. 2005;15(suppl 6):4-17.
  11. Bild DE, Bluemke DA, Burke GL, et al. Multi-Ethnic Study of Atherosclerosis: objectives and design. Am J Epidemiol. 2002;156:871-881.
  12. Key TJ, Appleby PN, Bradbury KE, et al. Consumption of meat, fish, dairy products, eggs and risk of ischemic heart disease: a prospective study of 7198 incident cases among 409,885 participants in the Pan-European EPIC cohort. Circulation. 2019; Epub ahead of print.
  13. Qin C, Lv J, Bian Z, et al. Associations of egg consumption with cardiovascular disease in a cohort study of 0.5 million Chinese adults. Heart. 2018;104:1756-1763.
  14. Vincent MJ, Allen B, Palacios OM, Haber LT, Maki KC. Meta-regression analysis of the effects of dietary cholesterol intake on LDL and HDL cholesterol. Am J Clin Nutr. 2019;109:7-
  15. Clarke R, Frost C, Collins R, Appleby P, Peto R. Dietary lipids and blood cholesterol: quantitative meta-analysis of metabolic ward studies. BMJ. 1997;314:112-117.
  16. Jacobson TA, Ito MK, Maki KC, et al. National Lipid Association recommendations for patient-centered management of dyslipidemia: part 2. J Clin Lipidol. 2015;9(6 Suppl):S1-S122.e1.

 

Photo by Annie Spratt