The Harrell Study and Seven Follow-Up Studies: A Brief Review

In 1981, R.F. Harrell and coworkers reported substantial IQ gains and other benefits in a partially double-blind, exploratory study of nutritional supplements and thyroid given to mentally retarded children (Harrell, Capp, Davis, Peerless & Ravitz, 1981). These findings attracted wide interest, controversy, and seven follow-up studies to date. The purpose of this review is to present a brief overview of these eight studies and to evaluate the scientific status of the issues raised by the Harrell study. In the original study, sixteen school-age children living at home (IQ 17-70) received dietary advice and nutritional supplements or placebos during a planned 8-month study. Desiccated thyroid was also given throughout to 13 of the subjects, as required to maintain morning axillary temperature at 36.6° C or above (Barnes method). The supplement contained 11 vitamins, most in large amounts, and 8 minerals in moderate amounts. During the first 4-month period (double blind), the 5 children receiving supplements (and thyroid) recorded average IQ gains of 5 to 10 points, depending on the investigator. However, the 11 placebo (and thyroid) subjects showed negligible average change (1 point), indicating that thyroid alone did not increase IQ in this experiment. In the second 4-month period, both groups received supplements plus thyroid. The IQs of the prior placebo subjects increased a reported 10 points on average, especially in the younger subjects, while some of the previously supplemented