Do you take antihistamines before going for a run outdoors? Bad idea: according to a new study, antihistamines make you sweat for nothing by canceling out the benefits of exercise on the cardiovascular system, blood sugar, and recovery.
Regular training improves athletic performance unless you are allergic to pollen and are taking medication. Scientists at Ghent University (Belgium) and the University of Copenhagen (Denmark) have made a surprising discovery: antihistamines, which are often prescribed for hay fever or hives, sabotage some of the benefits of exercise. These drugs reduce the increased blood flow to muscles during exercise by 35%.
“Aerobic exercise has a powerful preventive effect on cardiovascular, metabolic and chronic diseases,” explains Wim Derave, a sports physiologist at Ghent University and lead author of the study published in Science Advances. “Blocking histamine receptors prevents these microvascular and mitochondrial adaptations. As a result, the improvement in athletic capacity, glycemic control, and vascular function is reduced,” explains the scientist.
Antihistamines targeting H1 receptors are generally made with cetirizine, loratadine, or desloratadine. They are particularly indicated for rhinitis, conjunctivitis, and allergic urticaria. H2 antihistamines act on the receptors of the gastric mucosa, responsible for stomach acidity. They are mainly used in gastroesophageal reflux disease.
Histamine, a potent mediator of the adaptive response to sport
Histamine is generally associated with allergic reactions and gastric acid secretion, but in recent years research has shown that blocking histamine H1 and H2 receptors reduces blood flow to muscles after exercise, preventing adequate recovery. Blocking histamine receptors also alters the transcription of about a quarter of the genes, which are expressed differently after exercise, says physiologist John Halliwilli, who was not involved in the study.
To better observe the effects of histamine, 20 men were put through an intense interval training program three times a week for six weeks.
The volunteers taking antihistamines trained at the same intensity as those not taking histamines, but did not get the same benefits.
One hour before each session, half of them received drugs that block histamine H1 and H2 receptors, and the other half a placebo. At the end of the six weeks, the volunteers in the first group experienced significantly less physiological improvement than those in the placebo group, particularly in glucose metabolism, the ability of mitochondria to produce energy, and the formation of new capillaries. “The volunteers who took antihistamines sweated just as much and worked just as hard as the others, but they did not get the same beneficial effects,” Wim Derave explained to the Inverse website.
Sport and medication do not always go hand in hand
Should you stop taking allergy medication if you exercise? It is advisable to remain cautious. In this case, the researchers used a combination of two types of medication (anti-H1 and anti-H2) that are rarely taken at the same time, and not in doses as high as those tested in the experiment (540 mg of fexofenadine and 300 mg of ranitidine – banned on the market since 2020 – or 40 mg of famotidine). “It is possible that with a dose adjustment or a longer training period these effects could be counteracted,” the authors state.
Antihistamines are not the only drugs that interfere with exercise. Metformin (used in the treatment of type 2 diabetes) or resveratrol (an antioxidant extracted from grapes) also inhibit the positive effects of exercise, especially in older people, as previous studies have shown.