Higher egg consumption associated with lower risk of incident type 2 diabetes in men

Virtanen J, Mursu J, Tuomainen TP  et al  
Am J Clin Nutr 2015; DOI: 10.3945/ajcn.114.104109

Background

In the search for modifiable risk factors for type 2 diabetes (T2D), dietary factors are a logical path to take, considering evidence from observational and experimental studies.
Egg consumption, as a major source of dietary cholesterol, has been implicated as a possible risk factor. It has been associated with impaired glucose metabolism [1] and increased inflammation [2] in animal models, and with elevated fasting glucose [3] and higher risk of T2D [4,5] in humans. Addition of eggs to the diet in randomised controlled trials, however, has reduced plasma insulin and insulin resistance [6], decreased inflammatory markers [7-9] and increased formation of larger and less-dense LDL and HDL particles [6,10].
The effect of egg consumption on the risk of T2D is unclear. This study therefore set out to investigate the association between egg consumption and risk of incident T2D in middle-aged and older men from eastern Finland. Egg consumption has previously been shown not to be associated with carotid atherosclerosis or risk of myocardial infarction in this study population [11]. Consumption of food was assessed at baseline with a guided food record of 4 consecutive days, one of which was a weekend day, including indication of portion sizes. The egg consumption variable reflected total egg consumption, including eggs in mixed preparations. Average follow-up duration was 19.3 years (SD: 6.6 years, range: 0.2-26.8 years, 45008 person-years).

Main results

• After adjustment for age, examination year and energy intake, a lower risk of T2D was seen with increasing egg intake (P-trend across quartiles: < 0.001), with the third egg intake quartile (median: 35 g/day) already showing the lowest risk (relative risk reduction third vs. lowest quartile (median intake: 9 g/d): 37% (95%CI: 17-52%, absolute risks: 13.2% in the 3rd vs. 21.0% in 1st quartile). Higher intake did not provide further risk reduction.
• Each additional egg per day (55 g) was associated with 30% lower risk (HR: 0.70, 95%CI: 0.55-0.90). Adjustment for cholesterol intake strengthened the association slightly.
• Cholesterol intake was not associated with the risk of T2D, after correction for age, examination year and energy intake. After further correction for confounders, cholesterol intake showed a similar risk pattern across quartiles to egg consumption. Further adjustment for egg consumption weakened the association.
• Higher egg intake was associated with modestly lower plasma glucose concentrations at baseline and at the 4-year examination, and with lower CRP at the 4-year examination.
• Dietary cholesterol was associated with higher glucose and insulin concentrations at baseline, in particular after adjustment for egg intake. No significant relations with glucose or insulin were seen after 4 years.
• Sensitivity analysis of the association between egg intake and T2D incidence after 10 years of follow-up also showed a lower risk of T2D with increasing quartiles of egg consumption.

Conclusion

In this prospective cohort of middle-aged and older Finnish men, higher egg intake was associated with lower risk of incident T2D. Looking into metabolic risk markers suggests an inverse relation with fasting plasma glucose and serum CRP, but not with serum insulin.
Adjustment for potential risk factors did not have a large impact on the observed associations, suggesting that in this study cohort egg consumption was not just a surrogate for some other unhealthy lifestyle factors that could explain the association with risk of T2D.
Eggs are a major contributor to cholesterol intake. Egg and cholesterol intake showed similar inverse associations with T2D risk, but the association with cholesterol intake mostly appeared to be accounted for by egg intake. Eggs are also a rich source of many nutrients that may affect health in a positive way. These findings suggest that recommendations to limit the consumption of eggs in a generally healthy population should not be based on a single food component like cholesterol.

Find this article online at The American Journal of Clinical Nutrition

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