A unique new study, published in the journal Science Advances, is suggesting antihistamines can blunt some of the beneficial effects of exercise. The research found histamine functioning may be vital to both the short and long-term benefits of exercise.
Histamines are probably most familiar to those who suffer from seasonal allergies. When your immune system mistakenly flags pollen or dust as a threat it triggers the release of histamines. These molecules boost blood flow to areas of the body triggered by an allergen setting of a chain of events many hayfever suffers would be familiar with.
Antihistamines help reduce those symptoms by binding to histamine receptors, blocking the histamine molecules from kicking off the inflammatory process. Most histamine research has focused on allergies, however, histamines do plenty more than that in the body including playing a role in gastric acid release from the stomach, serving as a neurotransmitter, and even influencing sexual function in men.
A curious, and little investigated, role for histamines is the influence it has on skeletal muscle in response to physical exercise. We know histamine receptors are widely expressed in skeletal muscle. We also know that histamine plays a role in the acute reductions in blood pressure immediately following exercise.
So the question this new study set out to answer was whether comprehensively blocking histamine receptors can impede some benefits of exercise. The research first looked at the acute effect of antihistamines on exercise response.
Eight subjects were recruited to perform an exercise session, once with a placebo and then on another day with antihistamines blocking two types of histamine receptors (H1 and H2). The researchers found antihistamines blunted the increases in muscle blood flow normally seen following exercise. Referred to as post-exercise muscle perfusion, blocking histamine receptors reduced this mechanism by about 35 percent compared to the placebo sessions.
The second phase of the study set out to understand the long term effects of this disruption. Eighteen subjects were blindly split in to two groups following the same exercise routine for six weeks. The active group took histamine blockers before every training session while the control group were given placebos.
“Clear, and expected, training adaptations were observed in the study group receiving placebo: increases in exercise performance, whole-body insulin sensitivity and NO-dependent vascular function,” explains Thisbaux Van der Stede on Twitter, one of the researchers working on the project. “However, outcomes related to exercise performance, and especially on a submaximal level, improved only a bit (or not at all for some outcomes) in the group receiving the histamine receptor antagonists.”
Investigating muscle biopsies showed reductions across several aerobic capacity measures in the histamine blocker group. Improvements to glucose tolerance and vascular function were also impaired by the antihistamines compared to those in the placebo group.
Wim Derave, senior author on the study, says it was surprising to see how significantly blunted the beneficial effects of exercise were by blocking the activity of a single molecule.
“They sweated just as much, they exercised just as much, and so there was nothing different - they couldn't see it either,” says Derave in an interview with Inverse. “The beneficial effects were not taking place, although they thought and they hoped that they would.”
The researchers note this study does not mean people should stop taking antihistamines before exercising. Van der Stede points out this research was done with higher chronic doses of antihistamines that are not analogous to real-world uses by allergy sufferers and he stresses caution at broad practical interpretation of the results.
“…we blocked H1 and H2 receptors (only H1 receptors are targeted to treat allergies), and with a higher dosage than in practice,” notes Van der Stede. “This was done to completely inhibit histamine signaling during exercise to study its physiological role.”
Perhaps a more compelling way to think about this new finding is whether it could inform future research into ways to optimize exercise. The researchers suggest it could be possible to develop novel drugs that amplify the beneficial physiological outcomes of exercise.
The new study was published in the journal Science Advances.
