Recent decades have seen a sharp increase in the incidence of both obesity and asthma. A link between these two conditions has long been suspected, but evidence has been scarce. New research published in the Proceedings of the National Academy of Sciences of the USA (17 July 2007) reveals that T helper 2 (TH2) cells, which contribute to the development of asthma via aberrant cytokine responses, also produce a protein called pro-melanin-concentrating hormone (PMCH) that is known to increase appetite. PMCH released into the circulation by TH2 cells in the asthmatic lung could stimulate the hypothalamus to enhance appetite.

“Our study provides evidence for a possible mechanism linking obesity and asthma. However, as people with asthma aren't always obese, we now plan to look at possible genetic polymorphisms, or variations, of PMCH to see the role they play,” said David Cousins, the lead author of the study ( The Times , 17 July 2007). Cousins proposes a scenario in which some obese people develop asthma, and as a result their TH2 cells produce PMCH, which stimulates appetite and results in additional weight gain ( The Guardian , 17 July 2007).

More research will be needed to determine whether PMCH can be targeted therapeutically. Tak Lee, the director of the Medical Research Council Asthma UK Centre, said: “What we do not know is whether this protein has other important effects which would be affected if you suppressed it.” (The Guardian, 17 July 2007)

David Haslam of the National Obesity Forum adds that although there are not yet any therapeutic implications, “Working out the mechanism, the links between diseases is important, and it adds to the growing body of evidence which gives obesity some form of genetic basis.” ( BBC News , 17 July 2007)