My immunologist said that my slightly low iga may be caused by my chronic stress. she said cortisol decreases iga production. true?

True.....: and there is a pretty wide range on IgA in the normal category. There is a specific disease when the IgA is ZERO, but :"low" is not "zero" and "low" is not associated with significant problems. and yes, stress (especially day/night shift changes) alter hormones and might reasonably lower IgA levels. http://www.ncbi.nlm.nih.gov/pubmed/20496079 but... in the one study, the OPPOSITE was found !