Preliminary Research in New Zealand
In New Zealand, Dr. Cantwell’s research discovered an unusual factor associated with both SLD and ADHD. Children who had Iron Deficiency Anemia in Infancy showed all of the characteristics of SLD and ADHD when neurologically and psychologically tested at the age of six in year 2 at elementary school.
Dr. Cantwell studied two groups of children known to be at high risk for iron-deficiency anemia in infancy. The children in both groups were similar except that one group received supplemental iron in the neonatal period to prevent any iron deficiency anemia, and the other (control) group did not receive this treatment. No nutritional counseling was given to the parents of each group. All children had regular blood tested in infancy for evidence of anemia. The children in the control group consistently developed significant anemia between 12 and 18 months of age, but none of the iron-treated children developed anemia.
At the age of six years, all children received individual general physical, neurological and psychological evaluations. There were marked and consistent differences between the groups. The parents of the iron-treated non-anemic children reported that these children had fewer respiratory, gastro-intestinal, and ear infections, fewer hospitalizations, and were much easier to rear and were behaviorally better than their siblings at a similar age. The children, who had anemia of infancy, were consistently inferior in every measure tested when compared to the iron-treated group who had no anemia. These included such measures as stature, head circumference, balance, heel-toe walking, manual dexterity, attention span, hyperactivity, and both learning and behavior problems both at home and at school. On the Stanford Binet Intelligence tests, the average IQ scores of the anemic children was 92, compared with an average of 96 in the non-anemic children. In addition, the previously anemic children had lower performance test scores compared to the non-anemic normal children. Also, the average scores on the Peabody picture vocabulary test were lower in the anemic group of children.
These signs of impairment of brain function, together with significant behavior control and learning difficulties are compatible with the presence of ADHD and SLD. The significant differences between the two groups appear to has be the long-term result of the anemia, and the reduced oxygen-carrying capacity of the blood circulating through the brain during a critical 12-8 month period of brain development. This reduction in oxygen to the brain probably persisted during the pre-school period and its results may well be irreversible.
Additional Research in the United States
Dr. Cantwell carried out a five year research study in Miami, Florida, where over 300 kindergarten children were tested using a test to identify those students with ADD/ADHD, and at high risk of SLD. 18% of the students met the DSM 1VB criteria for Attention Deficit Disorder. One year later in first grade, these same students were individually given the test to screen them for SLD. The test positive students were then referred to the school psychologist. Comprehensive psycho-educational evaluations confirmed the presence of SLD in every child referred for testing. The incidence of SLD in first grade students was 21.3%. Of the SLD positive students, 39% were classified as Severe in while the remainder were equally represented as Moderate or Mild categories.
Of the ADD-positive students in kindergarten, 68% also had SLD in first grade when tested by the school psychologist.
During each of the next three years after testing, the children identified with SLD by the Children’s LD Test, and subsequently confirmed as having SLD by the school psychologist, were monitored. The children’s teachers were asked to rate their academic achievement levels in Reading, Spelling and Math as follows:
1. Above grade level
2. At grade level
3. Below grade level
Almost without exception, in each of the subsequent three years, these children received below grade level achievement ratings of 3 in reading and/or spelling, and mostly 2’s and 3’s in math. Several of these children gave a history of retention in either kindergarten or first grade. This confirms the effectiveness of the Children’s LD Test in the early detection of SLD in first grade students.
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