To the Editor.—
Dr Pardridge1 has criticized the review of aspartame safety issues published in JAMA2 and suggested that adverse effects may arise from the phenylalanine content of aspartame. We disagree with Dr Pardridge's contention that available data show a potential for adverse effects at normal levels of aspartame use.To support his thesis, Dr Pardridge claims that data of Levy and Waisbren3 (correlating infant IQ with maternal plasma phenylalanine concentrations in hyperphenylalaninemia) show a 10.5-point drop in IQ of children per 250-μmol/L increment in maternal plasma phenylalanine concentration. Dr Pardridge claims that this effect is linear and applicable down to maternal plasma phenylalanine concentrations of 200 μmol/L or lower. Dr Pardridge ignores the fact that when data correlating IQ with normal blood phenylalanine concentrations (40 to 120 μmol/L) are added to the graph, the plot is clearly biphasic and shows a threshold effect. Indeed, Levy and
Lewis D. Stegink, Wilma L. Krause. The Safety of Aspartame. JAMA. 1987;258(2):205–206. doi:10.1001/jama.1987.03400020047026
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