Longitudinal Association of Egg Consumption Habits with Blood Lipids Among Chinese Adults: Results from the Prediction for Atherosclerotic Cardiovascular Disease Risk in China Project
Egg consumption has long been a topic of debate in nutritional epidemiology due to its dual role as a rich source of high-quality protein and dietary cholesterol. While guidelines in many countries advocate limiting cholesterol intake to maintain ideal lipid profiles, the relationship between habitual egg consumption and blood lipid levels remains contentious, particularly in non-Western populations. This study, conducted within the framework of the China-PAR (Prediction for Atherosclerotic Cardiovascular Disease Risk in China) project, provides critical longitudinal insights into how varying levels of egg intake influence lipid metabolism among Chinese adults, a population with distinct dietary patterns compared to Western cohorts.
Research Context and Objectives
The China-PAR project, a large-scale national initiative, investigates cardiovascular disease risk factors across the Chinese population. Leveraging data from two study waves (2007–2008 and 2012–2015), this analysis aimed to elucidate the longitudinal effects of habitual egg consumption on five key lipid indicators: total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and non-HDL cholesterol (non-HDL-C). The study addressed gaps in existing literature by focusing on moderate egg intake levels, which are more representative of typical consumption patterns in China, and by extending observation periods beyond the short durations typical of randomized controlled trials (RCTs).
Methodology and Participant Characteristics
The study cohort included 60,952 adults after excluding individuals using lipid-lowering medications or lacking essential dietary or lipid data. Egg consumption was assessed via standardized food frequency questionnaires (FFQs) administered during face-to-face interviews. Participants reported the frequency and quantity of egg intake over the preceding year, with amounts converted to weekly counts (1 egg ≈ 50 g). Based on intake levels, participants were stratified into three groups: low (<3 eggs/week), moderate (3–<6 eggs/week), and high (≥6 eggs/week).
Fasting blood samples were analyzed for lipid profiles using enzymatic methods:
- TC: Cholesterol oxidase method
- TG: Glycerophosphate oxidase method
- HDL-C: Direct chemically modified enzyme method
LDL-C was calculated using the Friedewald formula (LDL-C = TC − HDL-C − TG/5), and non-HDL-C was derived as TC − HDL-C.
Statistical Approach
Generalized estimating equations (GEE) with unstructured correlation matrices were employed to model longitudinal associations between egg consumption categories and lipid levels. Adjustments were made for covariates including age, sex, urbanization, geographic region, body mass index (BMI), smoking, alcohol use, education, income, ideal diet score, and dairy intake. Sensitivity analyses further adjusted for hypertension and diabetes or excluded individuals with metabolic diseases (obesity, diabetes, hypertension).
Key Findings
1. Moderate Egg Intake and Favorable Lipid Profiles
Participants consuming 3–<6 eggs/week exhibited significantly improved lipid profiles compared to the low-intake group (<3 eggs/week):
- TC: Decreased by 0.606 mg/dL (95% CI: −1.129 to −0.084)
- TG: Reduced by 1.465 mg/dL (95% CI: −2.852 to −0.079)
- LDL-C: Lowered by 0.848 mg/dL (95% CI: −1.318 to −0.377)
- Non-HDL-C: Declined by 1.071 mg/dL (95% CI: −1.581 to −0.561)
- HDL-C: Increased by 0.461 mg/dL (95% CI: 0.240–0.682)
These results underscore a protective association between moderate egg consumption and lipid metabolism, aligning with Chinese dietary guidelines recommending 3–6 eggs/week for cardiovascular health.
2. High Egg Intake and Adverse Lipid Effects
In contrast, high egg consumption (≥6 eggs/week) was associated with elevated levels of atherogenic lipids:
- TC: Increased by 1.795 mg/dL (95% CI: 1.315–2.275)
- LDL-C: Rose by 1.763 mg/dL (95% CI: 1.337–2.189)
- Non-HDL-C: Heightened by 0.917 mg/dL (95% CI: 0.452–1.381)
Despite these adverse trends, high intake retained beneficial effects on TG (−4.208 mg/dL; 95% CI: −5.485 to −2.931) and HDL-C (+0.815 mg/dL; 95% CI: 0.612–1.018), suggesting complex interactions between egg components and lipid pathways.
3. Robustness of Results
Sensitivity analyses confirmed the stability of these associations:
- Adjusting for hypertension and diabetes did not alter the direction or magnitude of effects.
- Excluding individuals with metabolic diseases (n=33,025) preserved the core findings, though effect sizes varied slightly (e.g., TC reduction of 0.889 mg/dL in the moderate group).
Mechanistic and Comparative Insights
Egg yolks, while cholesterol-rich, contain bioactive compounds like phospholipids, carotenoids, and vitamins that may modulate lipid metabolism. The study’s divergent findings for moderate versus high intake suggest a threshold effect, where benefits of nutrients like phospholipids (which enhance HDL-C and inhibit intestinal cholesterol absorption) may be offset by excessive cholesterol intake at higher consumption levels.
Comparisons with prior studies highlight contextual variability:
- A Mediterranean cohort reported HDL-C reductions with >4 eggs/week, contrasting with the HDL-C elevation observed here.
- The multinational PURE study found no significant lipid changes with ≥7 eggs/week, potentially reflecting population differences in genetic, dietary, or lifestyle factors.
Limitations and Future Directions
While pioneering in its focus on a Chinese population, the study has limitations:
- Dietary Assessment: FFQs did not capture eggs consumed in mixed dishes (e.g., baked goods) or differentiate preparation methods (e.g., fried vs. boiled), which may influence cholesterol bioavailability.
- Causal Inference: Observational designs cannot fully exclude residual confounding, though longitudinal data strengthen evidence over cross-sectional studies.
- Generalizability: Findings may not extend to other ethnic groups or dietary contexts.
Public Health Implications
This research provides actionable guidance for dietary recommendations in China and similar settings:
- Promote moderate egg consumption (3–<6 eggs/week) to optimize lipid profiles.
- Discourage excessive intake (≥6 eggs/week) to avoid LDL-C and TC elevation.
- Tailor guidelines to regional dietary patterns, recognizing that global “one-size-fits-all” advice may not apply.
Conclusion
By longitudinally tracking egg consumption and lipid changes in a large Chinese cohort, this study clarifies the nuanced relationship between dietary habits and cardiovascular risk factors. It advocates for a balanced approach to egg intake, emphasizing moderation to harness nutritional benefits while mitigating cholesterol-related risks. Future research should explore interactions between egg consumption, genetic factors, and overall dietary patterns to refine personalized recommendations.
DOI: 10.1097/CM9.0000000000001555
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