The risk of coronary heart disease among women with type 2 diabetes appears to be elevated for those who consume high levels of heme iron and red meat, according to a large, long-term analysis from the ongoing Nurses' Health Study.
“Whether the increased iron intake is causally related to increased risk in CHD remains to be proven,” Dr. Lu Qi, of the department of nutrition at the Harvard School of Public Health, Boston, and colleagues wrote. “These findings suggest that patients with type 2 diabetes may consider reducing their consumption of heme iron and red meat for the prevention of CHD.”
The study included 6,161 women from the Nurses' Health Study who self-reported a physician diagnosis of type 2 diabetes between 1980 and 2000. The researchers excluded women with a history of CHD, stroke, or cancer as reported on follow-up questionnaires the women filled out prior to or during 1980 (Diabetes Care 2007;30:101–6).
At baseline, the women were divided into quintiles based on their median intakes of heme iron and red meat. The investigators then analyzed three of those five quintiles. In quintile 1, the median intakes were 1.70 mg/day and 0.55 servings per day, respectively. In quintile 3, the median intakes were 2.23 mg/day and 1.22 servings per day, respectively. In quintile 5, the median intakes were 2.83 mg/day and 2.39 servings per day, respectively.
During the follow-up period, which included 54,455 person years, the researchers documented 550 cases of CHD among the 6,161 women. These included 259 nonfatal myocardial infarctions, 153 CHD deaths, and 138 bypass operations or angioplasties.
After the researchers adjusted for age and body mass index, they found that women who consumed high levels of heme iron and red meat faced a significantly increased risk of fatal CHD, coronary revascularization, and total CHD, compared with those who consumed lower levels. The risk of total CHD was 50% greater among women who consumed the highest levels of heme iron compared with those who consumed the lowest levels.
The associations remained consistent when the researchers adjusted for level of physical activity, aspirin use, duration of diabetes, and other covariates.
Subanalysis revealed that postmenopausal women were at greater risk of CHD, compared with premenopausal women. “Premenopausal women may lose a significant amount of iron during menstruation, which may dilute the relationship between iron intake and CHD risk,” the researchers hypothesized.
They acknowledged limitations of the study, including its self-reported nature and “the possibilities of residual confounding because of imperfect measures of diet and lifestyle factors.”
The study was funded by the National Institutes of Health.