A Health Benefit of Roller Coasters

In a unique, home-spun experiment, researchers found that centripetal force could help people pass kidney stones—before they become a serious health-care cost.

Kidney stones in a jar in Wartinger's office (G.L. Kohuth / Michigan State University)

East Lansing, Michigan, becomes a ghost town during spring break. Families head south, often to the theme parks in Orlando. A week later, the Midwesterners return sunburned and bereft of disposable income, and, urological surgeon David Wartinger noticed, some also come home with fewer kidney stones.

Wartinger is a professor emeritus at Michigan State, where he has dealt for decades with the scourge of kidney stones, which affect around one in 10 people at some point in life. Most are small, and they pass through us without issue. But many linger in our kidneys and grow, sending hundreds of thousands of people to emergency rooms and costing around $3.8 billion every year in treatment and extraction. The pain of passing a larger stone is often compared to child birth.

For years in practice, Wartinger noticed anecdotal reports from patients who had passed small kidney stones during and immediately after visiting the Disney theme parks. It was a correlation he might not have noticed in another place, he told me: “This mass migration helped bring it to my attention.”

But one particular gentleman really inspired Wartinger. The man rode Big Thunder Mountain Railroad at Disney’s Magic Kingdom, and then passed a small stone. Then he did it again and passed another. And then another. “That was just too powerful to ignore,” Wartinger said. “I'd been hearing these anecdotal stories for a couple years, and then I thought, okay, there's really something here.”

The model kidney that Wartinger filled with stones and
urine, then brought on a roller coaster.
(G.L. Kohuth / Michigan State University)

If there were a way to make people pass stones while they were still small, Wartinger realized, the potential benefits could be enormous.

So Wartinger compiled people’s stories, and he realized that the common factor was having ridden Big Thunder Mountain Railroad. He found anecdotal reports of people passing stones after bungee jumping, but no research on this bodily-movement approach. So he decided to take things into his own hands and do a proper study.

First, Wartinger used a 3-D printer to create a clear silicone model of that three-time-stone patient’s kidney. He then filled the kidney with stones and urine. (Not real urine, I assumed, as I know the park already has plenty.) Then he and colleague Marc Mitchell bought two tickets and flew to Orlando.

Of course, the researchers had to get permission from Disney World before bringing the model kidney onto the rides. “It was a little bit of luck,” Wartinger recalls. “We went to guest services, and we didn't want them to wonder what was going on—two adult men riding the same ride again and again, carrying a backpack. We told them what our intent was, and it turned out that the manager that day was a guy who recently had a kidney stone. He called the ride manager and said, do whatever you can to help these guys, they're trying to help people with kidney stones.”

Other parks, Wartinger says, “have reacted anywhere from lukewarm to really not sure what to do with us.”

The two held the backpack between them “at kidney height” to try to subject the model to the same forces that a person would experience. A stone was counted as “passed” if it moved from a starting location lodged in a calyx and fell down into a trap at the point where the kidney meets the ureters. None of the stones or fluid actually spilled out during the roller coaster ride. (The research protocol notes: “Care was taken to protect and preserve the enjoyment of the other guests at the park.”)

“What was amazing was within just a few rides it became obvious that there was a huge difference in passage rates whether you sat in the front or the rear of the coaster,” Wartinger tells me. “There was a lot more whipping around in that rear car.”

The stones passed 63.89 percent of the time while the kidneys were in the back of the car. When they were in the front, the passage rate was only 16.67 percent. That’s based on only 60 rides on a single coaster, and Wartinger guards his excitement in the journal article: “Preliminary study findings support the anecdotal evidence that a ride on a moderate-intensity roller coaster could benefit some patients with small kidney stones.”

Now, though, he has done more than 200 total stone rides on Big Thunder Mountain Railroad. But that doesn’t mean it’s the only coaster that could be therapeutic: “Some rides are going to be more advantageous for some patients than other rides. So I wouldn't say that the only ride that helps you pass stones is Big Thunder Mountain. That's grossly inaccurate.”

There are other kidney designs to consider, too, as every person’s calyceal system is different, like a fingerprint. But the idea is that if you rode a variety of roller coasters in a short period of time, that would help you pass small stones and lingering sediment before it accumulates into debilitating, costly, obstructive stones.

Wartinger (G.L. Kohuth / Michigan State University)

Still to know if this works for sure, he’d need a prospective clinical trial using real people with real kidneys. I suggested that would be difficult. He said no, he has it all planned out: Take people with kidney stones and do an ultrasound before the ride and after, and see if the stone moves. Wartinger couldn’t do that right away because universities’ institutional review boards would require experimental evidence to prove the concept first.

This he seems to have done duly on Big Thunder Mountain Railroad, with attention to detail. For example, I thought I was just clarifying one such detail when I asked if the “urine” described in the model he brought to Disney was actually water. It was water, right?

“No, it was urine. It was mine.”

I still wasn’t sure if he was serious. I have no problem with urine, it’s just the idea of showing up at Disney with a urine-loaded kidney in your backpack.

“Yeah, I used dilute urine. I spent my life playing in pee. I don't have that aversion to urine that most people have. The reason I didn't use water is it would've put another variable in there that wasn’t real. So I used real urine … to avoid criticism.”

It seems he thought of everything. Including the fact that people will hear about this study and act on it before it’s validated in human trials. So his advice for now: If you know you have a stone that's smaller than five millimeters, riding a series of roller coasters could help you pass that stone before it gets to an obstructive size and either causes debilitating colic or requires a $10,000 procedure to try and break it up. And even once a stone is broken up using shock waves, tiny fragments and “dust” remain that need to be passed. The coaster could help with that, too.

For people who hate roller coasters, like a number of people I’ve run this idea by, the ultimate goal would be a more clinical experience—a way to move people in a controlled environment that would help them pass stones organically. Instead of sending people to a theme park, you might go down the hall to a 3-D rollercoaster with a prescription for a precise pattern of pitches, yaws, and rolls designed around your particular kidney anatomy and the location of your particular stone.