Multifactorial determinants of cognition — Thyroid function is not the only one

• Untreated hypothyroidism, i.e. hypothyroxinemia, can influence IQ.
• Thyroxine administration to euthyroid pregnant women has no effect on cognition.
• The hippocampus and NMDA receptors play a central role in cognitive processes.
• Antenatal and early life stressors can influence cognition later in life.
• Stressors can lead to decreased levels of magnesium and demands supplementation.

BackgroundSince the 1960s hypothyroidism together with iodine deficiency have been considered to be a principal determinant of cognition development. Following iodine supplementation programs and improved treatment options for hypothyroidism this relation might not be valid in 2015. On the other hand neurosciences have added different inputs also related to cognition.Scope of reviewWe will examine the characteristics of the original and current publications on thyroid function and cognition and also add some general determinants of intelligence and cognition. One central issue for us is the relation of stress to cognition knowing that both physical and psychological stress, are frequent elements in subjects with thyroid dysfunction. We have considered a special type of stress called pre-natal stress which can influence cognitive functions. Fear and anxiety can be intermingled requiring mechanisms of fear extinction.Major conclusionsRecent studies have failed to show an influence of thyroid medication during pregnancy on intellectual development. Neuroscience offers a better explanation of cognition than hypothyroidism and iodine deficiency. Additional factors relevant to cognition are nutrition, infection, prenatal stress, and early life stress. In turn stress is related to low magnesium levels. Magnesium supplementation can correct both latent hypothyroidism and acquired mild cognitive deficits.General significanceCognition is a complex process that depends on many determinants and not only on thyroid function. Magnesium deficiency appears to be a basic mechanism for changes in thyroid function as well as of cognition.

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