It’s one of the most valuable interventions for bolstering long-term wellbeing and maintaining independence in your later years, but for some people exercising can pose serious health risks.
For a small percentage of the global population – approximately 0.05 to 2 per cent – physical exertion is associated with symptoms that range from unpleasant to potentially fatal, due to an allergy known as exercise-induced anaphylaxis (EIA).
The condition is a rare, severe and potentially life-threatening allergic reaction triggered by exercise.
“In effect, the body reacts to physical exertion in much the same way it might react to a wasp sting,” says Dr Scott Pereira, consultant immunologist at Harley Street’s Medical Express Clinic in London.
Cases of EIA are rare and under-recognised, but lifetime prevalence is estimated to be around 0.05 per cent, with the condition accounting for approximately 5 per cent of all cases of anaphylaxis.
“It most commonly begins during the teenage years or 20s and affects around twice as many women as men,” says Pereira.
What triggers exercise-induced anaphylaxis?
For those with EIA, exercise alone is enough to trigger a reaction. More commonly, however, an episode occurs when exercise follows another anaphylaxis trigger – in many cases, this is a food eaten within the previous four to six hours.
The key issue, according to Pereira, is the combination. “A person may be able to eat the food without any problem while at rest, and they may be able to exercise safely on an empty stomach. Put the two together, however, and they experience a reaction,” he explains.
Not all foods trigger EIA – often, it is those commonly associated with major food allergies.
“Wheat is the classic culprit, specifically a protein called omega-5 gliadin,” says Pereira. Shellfish, tomatoes, nuts and celery are also known triggers.
“Other important co-factors include anti-inflammatory painkillers such as ibuprofen, alcohol, pollen exposure, infections and hormonal changes. These do not cause the reaction themselves, but they lower the threshold at which it occurs.”
The type, intensity and duration of exercise that can trigger an EIA episode are all unknown and thought to differ from person to person.
However, one study found a link between EIA and aerobic activities, such as running and brisk walking.
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How to tell if you’re allergic to exercise
An EIA episode often begins with tiredness and a sensation of warmth and itching, according to Pereira, before progressing to hives, swelling, stomach cramps, wheezing and, in severe cases, collapse.
Symptoms can come on quickly during exercise and, according to Anaphylaxis UK, can impede a person’s ability to breathe, and can also affect heart rhythm and blood pressure.
The charity highlights the most serious symptoms with its ABC method so people can quickly spot the warning signs and react appropriately:
A – airway: swelling of the throat, tongue or upper airways and difficulty swallowing
B – breathing: sudden onset wheezing or noisy breathing, difficulty breathing and persistent cough
C – circulation: feeling faint or dizzy, sudden fatigue, confusion, clammy skin, loss of consciousness or collapse
How does EIA differ from other allergies?
If EIA sounds somewhat similar to a severe food allergy, that’s because the underlying mechanism is the same as in other allergic reactions, according to Pereira.
“Immune cells called mast cells release large amounts of histamine and other chemicals, leading to hives, swelling and a drop in blood pressure,” he says.
Scientists still don’t fully understand why exercise triggers this process.
“The leading theory is that exercise increases the permeability of the gut, allowing greater absorption of food allergens than would occur at rest,” Pereira explains.
But, he adds, the key differentiating factor is timing. “A peanut or pollen allergy will generally occur whenever the person encounters the allergen, regardless of whether they are exercising.”
Pereira continues: “With exercise-induced anaphylaxis, physical exertion forms part of the equation. If someone reacts while running but can tolerate the same food perfectly well at rest, that pattern is a very important clue.”
What makes exercise-induced anaphylaxis particularly challenging, according to Pereira, is its unpredictability.
“Someone may experience several relatively mild episodes and then, on a hot day or after consuming alcohol, suddenly develop a much more severe reaction.”
How is EIA diagnosed?
Unfortunately, it’s not always easy to get an EIA diagnosis if you suspect you have the condition.
Pereira warns that diagnosis is often delayed by years simply because people – those experiencing symptoms and medical professionals alike – do not realise that exercise may be part of the problem.
“Diagnosis is based primarily on clinical history, plus allergy blood tests following a full consultation,” he explains.
“We look closely at what the person was doing, what they had eaten beforehand, whether they had taken painkillers and even factors such as the time of year or stage of the menstrual cycle.”
A clear pattern usually emerges that points towards the diagnosis, although not always in the way patients expect.
“I recently saw a patient who had spent years convinced that AstroTurf on a sports pitch was the trigger, when testing ultimately confirmed exercise-induced anaphylaxis instead,” Pereira says.
How is EIA treated?
There’s currently no known cure for EIA, but Pereira says that most people are able to continue exercising safely once they understand and avoid their triggers.
“The non-negotiable is carrying an adrenaline auto-injector, ideally two, at all times,” he says. “If symptoms begin, exercise should be stopped immediately and adrenaline used early rather than waiting to see whether symptoms worsen.”
If food is a suspected or known trigger, Pereira advises maintaining a gap of at least four hours between eating the trigger food and exercising.
“It is also sensible to avoid anti-inflammatory painkillers and alcohol around exercise, take extra care during hot weather and high pollen seasons, and avoid exercising alone until the condition is well controlled," he says.
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