Eye-Blinking Rates Are Slower in Infants with Iron-Deficiency Anemia than in Nonanemic Iron-Deficient or Iron-Sufficient Infants

Abstract

Iron deficiency has been shown to impair dopamine functioning in rodent models, but it is challenging to obtain evidence of such effects in human infants. Because spontaneous eye-blink rate may provide a noninvasive assessment of dopamine functioning, we hypothesized that eye-blink rate would be lower in infants with iron-deficiency anemia and would increase with iron therapy. A 4-min eye-blink assessment was conducted for quiet, alert infants sitting on their mother’s lap. Data were available for 61 9- to 10-mo-old infants from inner-city Detroit (19 iron-deficient anemic, 23 nonanemic iron-deficient, and 19 nonanemic iron-sufficient). Iron-deficient and iron-sufficient nonanemic groups had similar eye-blink rates (P = 0.90) and were therefore combined. We used Poisson regression based on generalized estimation equation methodology to test for differences between iron-deficient anemic and nonanemic infants in blinks/min and change after 3 mo of iron therapy. Iron-deficient anemic infants had a lower initial eye-blink rate than nonanemic infants (mean ± SD) (4.0 ± 1.9 vs. 5.3 ± 2.8 blinks/min; P = 0.02; effect size = 0.6 SD). At 12 mo, eye-blink rate increased by 2.1 blinks/min in the iron-deficient anemic group (P = 0.008); there was no change in the nonanemic group (P = 0.96). These results are consistent with reduced dopamine function in iron-deficient anemic infants. The clinical importance of a lower eye-blink rate is unclear, but impaired dopamine functioning is likely to have broader impact, given the role dopamine plays in regulating movement, motivation, cognition, and hormone release.