What it means:
There isn’t much literature available on the link between obesity and allergies, so possible explanations for the associations seen in these two studies are simply theories at this point, Visness says. In her study, she suggested that inflammation could play a role. Fat cells release cytokines, chemicals that promote inflammation, and an allergic reaction triggers inflammation as well. So people with high levels of inflammation in their bodies are likely to suffer from both conditions.
Another theory suggested in the Yale study was that histamine, which is the neurotransmitter that overreacts when you come into contact with an allergen, has a secondary role in regulating your appetite. Animal studies have shown that dosing mice with histamine reduces their food intake, while dosing them with antihistamines increases their appetites. Therefore, it stands to reason, the authors noted, that if you take a lot of antihistamines, that might cause you to eat more. (Some older antihistamines are even used as appetite stimulants in young children.)
Then there are even more basic explanations. “Some older medications are so sedating that they cause you to be a couch potato,” says Jackie Eghrari-Sabet, MD, a fellow of the American College of Allergy, Asthma and Immunology and an allergist with a private practice in Gaithersburg, MD. Drugs that make you that tired are more than likely to interfere with your getting regular exercise. Secondly, she says, antihistamines can dry you out and make you thirsty. “In some people, the signal for thirst can be confused with the signal for hunger,” she adds, making you more likely to eat when you really should be reaching for a glass of water.