Relationship between anxiety/depression and nausea: causal or associative?

The findings reported by Haug et al in a previous issue of this Journal [1] have an important bearing on the public health system. It has also been our clinical observation that symptoms referable to gastrointestinal system are very common in patients with depression/anxiety.

The authors have drawn conclusions that “the differential diagnosis for nausea should include both anxiety and depressive conditions.” This implies a causal role for anxiety/depression in producing nausea. While there is a possibility that nausea can indeed be caused by anxiety/depression, drawing conclusions about such a causal role from the kind of design the authors have followed becomes difficult.

Firstly, the temporal association between nausea and anxiety/depression is not investigated. Also, whether medical causes for nausea in the subjects who complained of it have been ruled out is not mentioned. In the absence of such information, the relationship between nausea and anxiety/depression can at best be termed as “associative” rather than causal. It is distinctly possible that those who had nausea for some medical reason would become anxious about their new symptoms and would obtain higher scores on anxiety scales.

Secondly, the authors have collected the data on nausea as “no complaints,” “minor complaints,” or “major complaints.” It is not clear how minor complaints were distinguished from major complaints. Moreover, analysis of the data does not mention which of these has been considered. A subject who experienced mild nausea for about half a day might have rated his nausea as “minor problem.” If he is grouped with subjects whose nausea was severe enough to seek medical help, such a grouping becomes arbitrary and the results based on that become less meaningful. Establishing criteria for nausea as a major complaint, and considering such subjects for analysis would have given more meaningful results.