Subclinical thyroid disorders and cognitive performance among adolescents in the United States.

BACKGROUND: Thyroid hormone plays a crucial role in the growth and function of the central nervous system. The purpose of the study was to examine the relationships between the status of subclinical thyroid conditions and cognition among adolescents in the United States. METHODS: Study sample included 1,327 adolescents 13 to 16 years old who participated in the Third National Health and Nutrition Examination Survey (NHANES III). Serum thyroxine (T4) and thyroid stimulating hormone (TSH) were measured and subclinical hypothyroidism, subclinical hyperthyroidism, and euthyroid groups were defined. Cognitive performance was assessed using the subscales of the Wide Range Achievement Test-Revised (WRAT-R) and the Wechsler Intelligence Scale for Children-Revised (WISC-R). The age-corrected scaled scores for arithmetic, reading, block design, and digit span were derived from the cognitive assessments. RESULTS: Subclinical hypothyroidism was found in 1.7% and subclinical hyperthyroidism was found in 2.3% of the adolescents. Cognitive assessment scores on average tended to be lower in adolescents with subclinical hyperthyroidism and higher in those with subclinical hypothyroidism than the score for the euthyroid group. Adolescents with subclinical hypothyroidism had significantly better scores in block design and reading than the euthyroid subjects even after adjustment for a number of variables including sex, age, and family income level. CONCLUSION: Subclinical hypothyroidism was associated with better performance in some areas of cognitive functions while subclinical hyperthyroidism could be a potential risk factor.

Blood concentrations of selected volatile organic compounds and neurobehavioral performance in a population-based sample.

The authors analyzed data from a national sample to examine the relationships between blood concentrations of selected volatile organic compounds (VOCs) and the assessment scores of neurobehavioral evaluation tests. They calculated summary statistics to describe blood concentrations of 30 VOCs. For instance, the 95th percentiles were as follows: 1,1,1-trichloroethane, 0.799 microg/l; 1,4-dichlorobenzene, 11.081 microg/l; benzene, 0.476 microg/l; and toluene, 0.281 microg/l. For 1,4-dichlorobenzene, benzene, dibromochloromethane, and trichloroethene, a blood level higher than the 95th percentile was associated with a poorer neurobehavioral assessment score than was a blood level up to the 95th percentile. The authors found a linear relationship between blood toluene concentration and the Serial Digit Learning Test score. The findings suggest that exposure to certain VOCs may result in poor neurobehavioral performance. The study was exploratory and precludes a conclusive statement, so further investigation is warranted.