Drs Levy and Waisbren abandon the linear relationship between the IQ of offspring and maternal plasma phenylalanine concentration that they previously reported1; this relationship was significant (r= -.82; P<.001). However, other authors2 have analyzed these data by linear regression to demonstrate the 10.5-point drop in IQ of the baby for each 250-μmol/L increment in maternal blood phenylalanine level. The issue of whether these data demonstrate that the deleterious effects on brain function caused by hyperphenylalaninemia follow a linear or threshold pattern is as yet unsettled. The fundamental question is whether plasma concentrations on the order of 200 μmol/L have harmful effects on the human central nervous system. This is important now because normal people may achieve this concentration of blood phenylalanine through excessive ingestion of aspartame. Drs Levy and Waisbren indicate that the intake of 10 mg/kg of aspartame products represents "ingestion of large amounts
Pardridge WM. The Safety of Aspartame-Reply. JAMA. 1987;258(2):206. doi:10.1001/jama.1987.03400020047027
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