Researchers may have finally put an end to a chicken and egg style debate on whether being underweight is a cause or a consequence of respiratory disease.
Writing in Thorax public health researchers from the University College London said research from the Prospective Studies Collaboration had shown that every 5-unit decrease in body mass index from 25 to 15 kg/m2 was associated with a 1.7-fold increase in respiratory mortality.
However the clinical importance of the findings was uncertain because it was unclear whether the association was causal or a consequence of illness-induced weight loss.
The likelihood that death is caused by an existing weight-modifying condition is highest in the earliest stages of follow-up and progressively diminishes over time, the researchers said.
They hypothesised that if the strength of the under- weight–mortality association attenuates when deaths occurring in earlier years of follow-up are removed from the analyses, reverse causation was a likely explanation.