Objective: To compare the incidence of iron deficiency anemia (IDA) between breast-fed (BF) and formulafed
(FF) infants and to identify the risk factors of IDA in these infants.
Design: Cohort study.
Material and Method: A study of 140 full- term infants (70 BF and 70 FF) was conducted at BMA Medical College and Vajira Hospital from February 2002 to November 2003. All infants were followed at the age of 1, 2, 4, 6, 9 and 12 months for growth and developmental assessment. Blood samples were analyzed for hemoglobin (Hb), hematocrit (Hct) and mean corpuscular volume (MCV) at 9-12 months; and infants with Hb < 11.0 g/dl were further investigated for the cause of anemia.
Results: The mean values of Hb, Hct, MCV and serum ferritin of BF infants were 10.8 g/dl, 32.8%, 70.9 fl and
16.7 ng/ml respectively, which were significantly lower than those of FF infants (11.4 g/dl, 35.1%, 73.3 fl, and 36.9 ng/ml, p < 0.05). Anemia was found in 27 BF infants (38.6%) compared with 10 FF infants (14.3%). The incidence of IDA in BF infants was significantly higher than FF infants (25.7% vs 2.9%, p < 0.001). Risk factors of IDA included low birth weight, breastfeeding and inadequate complementary food (adjusted RR (95% CI): 3.1(1.1-9.1), 6.3(1.5-25.0), 7.7(2.8-20.0), respectively).
Conclusion: IDA is more prevalent in BF than FF infants. Risk factors of IDA are low birth weight, breastfeeding
and inadequate complementary food. Prevention of IDA in infants should be achieved through adequate iron-rich complementary food and screening for Hb or Hct at 9-12 months of age in high risk infants.

Keywords: Anemia, Breastfeeding, Formula feeding, Infant, Iron deficiency anemia