Can Antihistamines Ruin Your Workout Gains? New Study Investigates Surprising Role of Histamine During Exercise

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When we hear the word histamine, most of us think of itchy eyes, sneezing, and allergy medication. A new study from the University of Oregon is flipping that image on its head. A new study finds that histamine—a molecule most commonly linked to allergic reactions—may play a critical role in optimizing aerobic exercise performance and post-exercise recovery.

Histamine: More Than Just an Allergy Trigger

Histamine is a naturally occurring molecule in our bodies to help the immune system react to allergens. It's what's released from mast cells when there's an allergic attack and leads to the classic symptoms we associate with hay fever, like runny noses and itchy eyes. That's why antihistamines such as loratadine and cetirizine are so popular—they suppress this reaction.

But histamine does more than induce allergy. It's found in a vast range of organisms, from one-celled organisms to people, and is a leading participant in many biological processes, like inflammation and blood flow.

How Histamine Makes Exercise Performance and Recovery Easier

The University of Oregon study looked at the way histamine works during and after aerobic exercise. Researchers found that histamine actually helps the body react to physical stress. Indeed, when histamine signaling was blocked using high doses of antihistamine medication, subjects' gains in fitness were significantly compromised.

16 adults cycled weekly for six weeks. Half received large doses of antihistamines before each session, and the rest received a placebo pill. The group that had received the placebo developed double the improvement in cardiovascular function after the study, as compared to the antihistamine group.

Researchers also detected better blood flow adaptation in the placebo group, an important aspect of long-term aerobic conditioning. Contrary to what one might expect, there was little disparity in VO₂ max between groups, despite researchers observing that the short study duration and limited sample size might have bounded these findings.

Why Histamine Matters for Muscle Repair and Growth

Exercise causes minute tears in muscle fibers, stimulating inflammation and muscle rebuilding. Histamine seems to facilitate this process by increasing the blood supply to contracting muscles and orchestrating an immune response that is favorable to adaptation and healing.

We have acquired an entire village of cell types that are activating programmes to reorganise and restructure and enhance the function of the skeletal muscle-organ system," added Professor John Halliwell, human physiologist and author of the study.

Histamine continues to work after the exercise session is over—keeping the immune system activated and aiding repair for optimal performance the next time. 

Histamine's Surprising Influence on Gene Expression

Another key discovery? Histamine controls which genes are switched on with exercise. Blocking histamine action knocked out nearly 25% of the roughly 3,000 genes that typically respond to exercise. This likely limited the creation of key proteins needed for fitness adaptation, recovery, and endurance.

This is in line with other recent studies, including one that looked at high-intensity interval training, which also saw that antihistamines suppressed improvement in cardiovascular function.

Do You Need to Stop Taking Antihistamines Before Exercise?

Not so fast. While these results are stunning, the study used antihistamine doses much greater than those in available-over-the-counter medication. It is still unknown whether standard allergy medication affects your workout performance likewise.

Professor Halliwill urges caution and emphasizes the need for further research: "The studies up to now have employed antihistamine doses considerably higher than typical over-the-counter doses. Further research is necessary to determine whether routine antihistamine use could suppress exercise adaptation."

Takeaway: Your Body's Hidden Fitness Ally

Histamine isn't just your nemesis when you experience an attack of allergy—a best-kept secret for increasing your stamina, muscular strength, and recovery. While further research needs to be done to identify how regular use of antihistamines will affect fitness, the message is clear: the body's inflammatory mechanisms, including histamine release, are responsible for how we adapt to physical stress.

So the next time you take that allergy pill before you go out for your jog, you might do a double take—at least wait for additional research on the topic.