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

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.