Association Between Iron Deficiency and A1C Levels Among Adults Without Diabetes in the National Health and Nutrition Examination Survey, 1999–2006

OBJECTIVE Iron deficiency has been reported to elevate A1C levels apart from glycemia. We examined the influence of iron deficiency on A1C distribution among adults without diabetes. RESEARCH DESIGN AND METHODS Participants included adults without self-reported diabetes or chronic kidney disease in the National Health and Nutrition Examination Survey 1999-2006 who were aged > or =18 years of age and had complete blood counts, iron studies, and A1C levels. Iron deficiency was defined as at least two abnormalities including free erythrocyte protoporphyrin >70 microg/dl erythrocytes, transferrin saturation <16%, or serum ferritin < or =15 microg/l. Anemia was defined as hemoglobin <13.5 g/dl in men and <12.0 g/dl in women. RESULTS Among women (n = 6,666), 13.7% had iron deficiency and 4.0% had iron deficiency anemia. Whereas 316 women with iron deficiency had A1C > or =5.5%, only 32 women with iron deficiency had A1C > or =6.5%. Among men (n = 3,869), only 13 had iron deficiency and A1C > or =5.5%, and only 1 had iron deficiency and A1C > or =6.5%. Among women, iron deficiency was associated with a greater odds of A1C > or =5.5% (odds ratio 1.39 [95% CI 1.11-1.73]) after adjustment for age, race/ethnicity, and waist circumference but not with a greater odds of A1C > or =6.5% (0.79 [0.33-1.85]). CONCLUSIONS Iron deficiency is common among women and is associated with shifts in A1C distribution from <5.5 to > or =5.5%. Further research is needed to examine whether iron deficiency is associated with shifts at higher A1C levels.