Many individuals suffering from allergies may turn to antihistamines for relief. Taking antihistamines year-round, rather than just when you have an allergic reaction, is the best way to stave off allergies, according to John Collard, clinical director of Allergy UK, in a 2012 "NHS Choices" article. Because histamines are a neurotransmitter, many people worry that taking an antihistamine to block them could impact everyday bodily functions, such as metabolism and calorie digestion. Learn the potential impacts of antihistamines on calories and metabolism to determine whether you should medicate that allergic reaction or suffer through the itching.
What are Histamines?
Allergens in the environment, such as pollen and mold, cause allergic reactions that start with the production of histamines. Histamines are neurotransmitters that cause your body to begin an inflammatory response to an allergen. This response involves blood-vessel growth, swelling and triggering various receptors to eliminate the irritant. The expansion of blood vessels and triggering of receptors cause skin redness, itchiness and headaches as the body works to fight off the allergen.
Histamine Production and Exercise
When you exercise, mast cells -- containing large amounts of histamines -- release histamine granules, causing an allergic reaction. Taking medication or eating food to which you are allergic before exercising may trigger histamine production, according to a 2008 study published in the "Journal of Investigational Allergology and Clinical Immunology." Exercise-induced histamine production can result in urticaria, angioedema or anaphylaxis, which involve varying degrees of red and itchy hives, swelling and airway constriction.
What are Antihistamines?
Antihistamines come in the form of tablets, liquids, eye drops and nasal sprays. They block certain histamine receptors, working to reduce and even eliminate the reactions generally caused by the associated allergen. Rantidine, also called Zantac, reduces stomach acid buildup by blocking receptor H2. Fexofenadine, also called Allegra, can be used to block receptor H1, reducing sneezing, itchy eyes and runny nose.
Calories and Metabolism
Although certain drugs have been linked to weight gain, no studies have turned up results linking antihistamines to calorie intake or metabolism. Some antihistamines make you drowsy, thus temporarily slowing your metabolism, but the effects are not lasting. Studies have shown that other medications that block histamine receptors, such as the antipsychotics olanzapine and clozapine, have a significant effect on weight gain. However, because antihistamine medication is taken less frequently and in a much smaller dosage, the effect on weight gain is negligible, as demonstrated in a 2006 "Proceedings of the National Academy of Sciences of the United States of America" article.
Some antihistamines can make you drowsy and should not be used when exercising, especially if your workout routine involves lifting or using machines. Stick to non-drowsy antihistamines before your workout and save the drowsy ones for bedtime. If you prefer to take drowsy antihistamines, read the bottle and talk to your physician to determine how long you should wait after taking the antihistamine before it's safe to exercise.
- NHS Choices: Hay Fever Tablets
- PNAS: Antipsychotic Drug-Induced Weight Gain Mediated by Histamine H1 Receptor-Linked Activation of Hypothalamic AMP-Kinase
- HealthGuidance: What Is a Histamine Reaction?
- Journal of Investigational Allergology and Clinical Immunology: Food-Dependent Exercise-Induced Anaphylaxis: Possible Impact of Increased Basophil Histamine Releasability in Hyperosmolar Conditions
Natasha Hochlowski holds a dual B.S. in chemistry and writing from Loyola University Maryland. She has been writing professionally since 2007, frequently contributing to "The Journal of Young Investigators," and has worked as a technical writer/editor for several major pharmaceutical companies.