Egg consumption and incident type 2 diabetes: are there any advantages to excessive consumption of eggs?

In a recently reported study entitled ‘‘Egg consumption and risk of incident type 2 diabetes in men: the Kuopio Ischaemic Heart Disease Risk Factor Study,’’ which was a long-term cohort study, Virtanen et al. (1) concluded that a higher intake of eggs was associated with a lower risk of the development of type 2 diabetes (T2D) in 2332 men aged 42–60 y at baseline. The same trend without statistical significance was observed in relation to higher cholesterol intake and a lower risk of T2D. The authors also conducted a trend analysis on fasting plasma glucose (FPG), serum insulin, and serum C-reactive protein (CRP) over a follow-up period of 4 y and reported that egg consumption was inversely associated with the FPG and serum CRP. I have a comment on the setting of the reference group in their analysis. A daily intake of 1 egg is considered to have no adverse effects on health, and the authors mentioned that the weight of a medium egg in their study was ;55 g. Namely, 377 subjects in the highest quartile (n 1⁄4 582) consumed at least 1 medium egg/d. From the information obtained, the authors should not have selected the lowest quartile as the reference group for their Cox regression analysis. The lowest and the second-lowest quartiles included subjects with poor nutritional intakes with respect to eggs and cholesterol, which would lead to an increase in incident T2D. The same situation can be observed in their trend analysis on FPG, serum insulin, and serum CRP. Linear trend analysis is not appropriate, and ANCOVA should be selected to analyze the elevated values of biomarkers in subjects in the lowest or second-lowest quartiles. The authors cited 2 articles by Djoussé et al. (2, 3), which reported the lack of any association between egg consumption or dietary cholesterol and the risk of development of T2D (2) and a positive association between egg consumption and the risk of development of T2D (3). In addition, Zazpe et al. (4) reported that egg consumption was not associated with the development of T2D by comparing the highest with the lowest quartile of egg consumption (,4 eggs/wk compared with .1 egg/wk) with an OR of 0.7 (95% CI: 0.3, 1.7). Virtanen et al. conducted a long-term cohort study by targeting middle-aged and older men at the baseline, and a sufficient number of events were observed. I suppose that a stable estimate of the development of T2D can be made only by the appropriate setting of the reference group, and their conclusion should be modified as ‘‘lower than recommended daily intake of egg is a risk factor for the development of T2D.’’