To establish the parameters of optimal nutrition do we need to consider psychological in addition to physiological parameters? 
The criteria used to establish dietary reference values are discussed and it is suggested that the too often the "need" they aim to satisfy is at the best vaguely specified.  The proposition is considered that if we aim to establish optimal nutrition we will gain from considering psychological in addition to physiological parameters.  The brain is by a considerable extent the most complex and metabolically active organ in the body.  As such it would be predicted that the first signs of minor subclinical deficiencies will be the disruption of the functioning of the brain.  The output of the brain is the product of countless millions of biochemical processes, such that if enzyme activity is only a few percentage points less than maximum, a cumulative influence would result.  A series of studies of micronutrient supplementation in well-designed trials were reviewed.  In metaanalyses the cognitive functioning of children and the mood and memory of adults has been shown to respond to multivitamin/mineral supplementation.  Given the concerns that have been expressed about the negative responses to high levels of micronutrients, the implications are discussed of the finding that psychological functioning may benefits from an intake greater than those currently recommended.