An egg a day raises risk of diabetes

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People who eat eggs every day may substantially increase their risk of type 2 diabetes, researchers here said.

Men with the highest level of egg consumption -- at seven or more per week -- were 58% more likely to develop type 2 diabetes than those who did not eat eggs, and women were 77% more likely to become diabetic if they ate at least an egg a day, Luc Djoussé, M.D., D.Sc., of Brigham and Women's Hospital and Harvard, and colleagues reported online in Diabetes Care.

Levels of egg intake above one a week also incrementally increased diabetes risk in both men and women (both P<0.0001 for trend), the researchers said.

Eggs are a major source of dietary cholesterol (about 200 mg per egg) and add about 1.5 g of saturated fat each to the diet, both of which would be expected to increase diabetes risk, they said.

But each egg also contributes about 0.7 g of polyunsaturated fat, which may confer a lower risk of type 2 diabetes, the researchers noted.

The limited, primarily animal model, evidence for an effect of eggs or dietary cholesterol on glucose metabolism has been inconsistent, they added.

To sort out the effects, the researchers analyzed two large prospective trials that included food frequency questionnaires.

Their analysis included 20,703 male physicians without baseline diabetes from the Physicians' Health Study I (1982-2007) and 36,295 similarly diabetes-free female health professionals from the Women's Health Study (1992-2007).

Both studies were originally designed as randomized trials of vitamin supplementation and aspirin for prevention of heart disease.

Over a mean follow-up of 20.0 years in men and 11.7 years in women, 1,921 men and 2,112 women developed type 2 diabetes.

Diabetes was more common in men and women who reported eating more than the average one egg a week.

After adjustment for traditional diabetes risk factors and compared with no egg consumption at the 95% confidence interval, the hazard ratios for type 2 diabetes in men were:

9% for less than one egg a week (hazard ratio 1.09, 0.87 to 1.37)
9% for one egg a week (HR 1.09, 0.88 to 1.34)
18% for two to four eggs a week (HR 1.18, 0.95 to 1.45)
46% for five to six eggs per week (HR 1.46, 1.14 to 1.86)
58% for seven or more eggs each week (HR 1.58, 1.25 to 2.01)

Updating egg consumption with longer follow-up among men strengthened the associations to an almost twofold risk for those in the near daily or higher intake groups (HR 1.77, 95% CI 1.39 to 2.26, and HR 1.99, 95% CI 1.23 to 3.23, respectively).

For women, the multivariate-adjusted risks, also at the 95% confidence interval, compared with no egg intake were:

6% for less than one egg per week (HR 1.06, 0.92 to 1.22)
-3% for one egg a week (HR 0.97, 0.83 to 1.12)
19% for two to four eggs per week (HR 1.19, 1.03 to 1.38)
18% for five to six eggs a week (HR 1.18, 0.88 to 1.58)
77% for seven or more per week (HR 1.77, 1.28 to 2.43)

Data on dietary cholesterol available in the female health professional study showed higher diabetes risk with rising dietary cholesterol with hazard ratios increasing to 1.28 (95% CI 1.10 to 1.50) in the highest quintile (P<0.0001 for trend).

Adjustment for dietary cholesterol attenuated the association between diabetes and egg consumption, whereas saturated fat was not associated with type 2 diabetes and did not alter the diabetes-egg link.

The effects did not appear to be limited to those with high carbohydrate diets, hypercholesterolemia, or high body mass index.

However, the researchers acknowledged that the data did not include repeat fasting glucose, fasting insulin, and other biomarkers of glucose metabolism to "comprehensively examine possible physiologic mechanisms."

The observational studies may also have been limited by self-reporting and residual confounding, they noted.

The generalizablity may have been limited as well by the homogeneous, primarily Caucasian health professional population, which may have different behaviors than the general population, Dr. Djoussé's group said.

"Given the societal burden of type 2 diabetes," they concluded, "confirmation of these findings in other populations and exploration of possible underlying biological mechanisms are warranted."

The study was supported by grants from the National Cancer Institute and the National Heart, Lung, and Blood Institute.

The researchers reported no conflicts of interest.

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Source: http://www.medpagetoday.com/cardiology/diabetes/11883?xid=ob_cc_Diabetes