Olympians with asthma are almost twice as likely to medal. Science has yet to determine why.

While watching the 2018 Winter Olympics in Pyeongchang, South Korea, you’ll probably hear about athletes with asthma.

In fact, odds are those athletes will be bringing home medals, too, because if you look at the data, they’re more than twice as likely as their counterparts to earn gold, silver, or bronze.

Data from the last five Olympic Games reveal that around 8 percent of participants have asthma. It’s the most common chronic condition they have.

Winter Olympians are more likely than athletes at the summer games to have asthma, possibly due to training in dry, cold conditions.

Nearly half of elite cross-country skiers, ice skaters, and hockey players have received a diagnosis of a respiratory condition.

Those numbers have led to speculation that asthma can actually be a boon to athletes, something observers have dubbed the “asthmatic advantage.”

But the research and the athletes themselves say otherwise.

“If anything, we fight to be normal,” said Joanna Zeiger, who placed fourth in the triathlon at the Sydney Games.

“For anyone who thinks this is an advantage, I invite them to watch me running up a hill when someone is cutting their grass alongside it,” she added.

So how is it that so many successful Olympians have asthma?

Does asthma make them better athletes, or does their training make them develop it?

Zeiger received her diagnosis of asthma at the age of 23, when she began adding running into her regimen after a lifetime of swimming.

“When I first really noticed the symptoms, I assumed I was out of shape and so I trained harder,” she told Healthline. “My dad, an allergist, suggested that maybe it was asthma.”

After learning that she indeed had asthma, Zeiger looked back on her career in swimming and something of an aha moment.

“I probably had it much longer than I realized, but the symptoms appeared so infrequently that we didn’t realize what was going on,” she said.

With a diagnosis in hand, however, Zeiger and her doctors began figuring out how to treat her condition.

“I’ve tried steroids, nasal sprays, long- and short-acting inhalers,” she outlined. “It’s been a huge challenge trying to control it. It’s still a struggle: Cold weather, pollen, and exercise all can set it off.”

In spite of that, though, Zeiger successfully competed in the Olympics, won the 2008 Ironman 70.3 World Championships, and has qualified for the Olympic marathon trials several times over.

Like many elite athletes with asthma, she’s figured out a way to make it work.

Dr. Tod Olin, a pediatric pulmonologist at National Jewish Health in Denver, says that research has spun differing theories into why so many elite athletes have asthma.

One such theory, for instance, is that endurance training can be an occupational hazard, leading to or worsening cases of asthma in this population.

“You’ve got a group of athletes that train longer and harder than others and over time, could this lead to asthma?” he asked. “Plus many of them train in adverse conditions — cold, polluted air, chlorine — all can be irritants.”

Indeed, a 2016 report from the medical journal Breathe found that a higher proportion of athletes developed asthma after the age of 25 than younger athletes, particularly in endurance sports.

The report concluded that long-term, demanding training could be a causative factor in asthma, and observed that the condition declined significantly once these same athletes retired.

Research has also delved into whether or not asthma can negatively impact an athlete’s VO2 max, or maximum rate of oxygen consumption.

VO2 matters because it means a person is able to suck in a lot of oxygen, transfer it into the bloodstream, and fuel muscles. Elite athletes tend to have a much higher VO2 max than the average athlete.

But a 2008 study in the Journal of Applied Physiology found that people with asthma were not at a disadvantage.

Olin says that for those speculating asthma is an advantage, you have to play devil’s advocate.

“You have to question whether or not elites really train that much harder or longer than amateurs,” he pointed out.

“Do elites with asthma might have some physiological changes that give them some benefit? Is it a nervous system change, for instance? It’s hard to say,” Olin said.

Still, other studies have investigated whether or not the common treatment for asthma — salbutamol — can have a positive impact on performance.

The working theory was that elite athletes have a genetic variant that caused them to respond to the drug in a way that offers them an advantage.

When tested in both healthy participants and those with asthma, however, the results proved otherwise.

Curiously, it seems like this theory is still accepted by top-tier athletes.

Two of Norway’s top cross-country skiers — Martin Johnsrud Sundby and Therese Johaug — received doping bans in 2016 for overuse of salbutamol.

An investigation by the Norwegian Ski Federation revealed that the team made the medication widely available, even among athletes without an asthma diagnosis.

Sundby will be on the roster in Pyeongchang, but Johaug’s original sentence was extended, barring her from the Winter Olympics.

At the end of the day, most researchers and doctors suggest that elite athletes with asthma have figured out a way to still perform at high levels, in spite of their condition.

One working theory is that elite athletes are religious about warming up before workouts and competitions, something that offers them a temporary reprieve from asthma attacks.

Zeiger said that perhaps in some ways, having asthma has kept her from overtraining, because it naturally keeps her in check.

“Other than that, it has always been a problem, not an advantage,” she said. “I’ve missed chunks of training, had to drop out of races, and pushed myself in situations that have led to full-blown attacks.”

The message, Olin told us, is that asthma shouldn’t keep anyone from training and progressing as an athlete: “The elites have proven that it doesn’t have to hold you back.”