Exposure to wildfire smoke increases the odds of being diagnosed with dementia even more than exposure to other forms of air pollution, according to a landmark study of more than 1.2 million Californians. The study — released Monday at the Alzheimer’s Assn. International Conference in Philadelphia — is the largest and most comprehensive review of the impact of wildfire smoke on brain health to date, according to its authors.

“I was expecting for us to see an association between wildfire smoke exposure and dementia,” said study author Dr. Holly Elser, an epidemiologist and resident physician in neurology at the University of Pennsylvania. “But the fact we see so much stronger of an association for wildfire as compared to non-wildfire smoke exposure was kind of surprising.”

The findings have big health implications, particularly in Western states, where air pollution produced by wildfires now accounts for up to half of all fine-particle pollution — a figure that’s been trending upward as wildfires grow larger and more intense due to climate change and legacies of fire suppression and industrial logging that have altered the composition of many Western forests.

The researchers looked at a type of particulate-matter pollution called PM2.5. These particles are 30 times smaller than the width of a human hair — tiny enough to penetrate deeply into the lungs and cross over into the bloodstream, where they can cause inflammation. Exposure has been shown to raise the risk of dementia and a host of other conditions, including heart disease, asthma and low birth weight.

“We increasingly see that PM2.5 is tied to virtually every health outcome we look at,” said study author Joan Casey, associate professor of public health at the University of Washington.

Elser, Casey and fellow researchers analyzed the health records of more than 1.2 million Kaiser Permanente Southern California members 60 or older between 2009 and 2019. None had been diagnosed with dementia at the beginning of the study.

They estimated each person’s exposure to PM2.5 based on their census tract of residence and then separated that into wildfire and non-wildfire pollution using air quality monitoring data, satellite imagery and machine learning techniques.

They then looked at how many participants were eventually diagnosed with dementia. Unlike past studies, the researchers were able to determine this using patients’ full electronic health records, rather than relying on hospitalizations as a proxy for such diagnoses.

Looking at participants’ average wildfire PM2.5 exposure over three years, the researchers found a 23% increase in the odds of a dementia diagnosis for each increase of 1 microgram of particulate matter per cubic meter of air. When it came to non-wildfire PM2.5 exposure, they documented a 3% increased risk of dementia diagnoses for each increase of 3 micrograms of particulate matter per cubic meter of air.

“That’s what it comes down to, is what’s so different about wildfire smoke?” Casey said.

More research is needed to learn exactly what that is. Possibilities include the fact that wildfire particles are produced at higher temperatures, contain a greater concentration of toxic chemicals and are, on average, smaller than PM2.5 from other sources.

These ultrafine particles can translocate from people’s noses into their brains via the olfactory bulb, Casey said.

“Normally the brain is protected by the blood-brain barrier, but here there’s actually a direct route for ultrafine particles to get into the brain and possibly cause some of the problems that we’re seeing in folks living with dementia,” she said.

The way in which people are exposed to wildfire smoke also differs from other types of fine-particle pollution, the researchers said. Background or ambient fine-particle pollution levels are usually relatively constant in a given place over time. But wildfire particulate matter tends to fluctuate wildly, resulting in more exposure over shorter periods of time, which may overwhelm the body’s defenses.

Of some 5,500 abstracts submitted to the Alzheimer’s Assn. International Conference, this one stood out due to its novelty, importance and impact, said Dr. Claire Sexton, senior director of scientific programs and outreach for the Alzheimer’s Assn.

“There have been other studies looking at different types of pollution, but this was unique in terms of the extent and the way in which it was able to do these analyses,” she said.

The researchers found the effects to be stronger on Asian, Black and Latino people, as well as those living in high-poverty areas. The most heavily impacted group was one that researchers classified as “other” because it didn’t contain enough people to differentiate further, Casey said. That group included Indigenous people, Pacific Islanders and people whose race was unknown.

“So these disparities are playing out again, as we unfortunately often see with environmental exposures,” she said. “But the level at which we observed it here was fairly striking.”

Casey believes those disparities are due to differential exposure based on where populations are located, noting that her previous research has shown that Indigenous people in California have by far the highest levels of wildfire particulate exposure. Other factors could include poorer housing quality, lack of access to air filtration devices, jobs that prevent people from staying indoors during wildfire events and disparate responses to the same amount of pollution due to preexisting hypertension or diabetes, she said.

“All those things are driven by social determinants of health,” she said. “The fact that we need to allocate additional resources to these people and places to protect health and to try to reduce health disparities going forward is really important.”

The researchers did not differentiate between dementia subtypes like Alzheimer’s, the most common form, because they relied on diagnostic codes rather than using brain imaging or postmortem studies. That’s important to know — and a key area for future study — because in order to best protect people, clinicians need to have an understanding of what’s underpinning the relationship between wildfire smoke and different dementia subtypes, Elser said.

Still, the study is notable for its massive sample size and careful approach, taking into account sociodemographics like comorbidities and census tract poverty, said Rachel Whitmer, the director of the UC Davis Alzheimer’s Disease Research Center who was not involved in the research.

The prevalence of dementia is on the rise as the baby boomer generation ages, but environmental factors may also be contributing to the increase, she said.

Research like this lays the groundwork for future studies, she said.

“With the increase in wildfires, this is a really important question and I think they did a really rigorous job in exploring it,” she said.

Levels of PM2.5 had been declining since the Clean Air Act took effect in 1970. But wildfires have reversed those trends in California, undercutting efforts to reduce emissions. In recent years, wildfire smoke has also affected the Midwest and East Coast. In 2023, smoke from Canadian wildfires blanketed the Atlantic seaboard, triggering air quality alerts and forcing the cancellation of outdoor events.

“It’s a big problem in places where wildfires are endemic,” Elser said. “And I worry that as we continue to experience increasingly frequent wildfire events, this could affect more people over a larger geographical distribution, more of the time.”

The most decorated gymnast ever sprints down the vault runway. She tumbles gracefully onto the springboard, flings herself backward onto the vault table and pops off the surface. Soaring through the air, she folds her body in half and grabs the back of her legs for two head-over-heels flips.

The crowd erupts when Simone Biles stomps her feet into the mat.

Another successful Yurchenko double pike.

“It just makes your mouth drop open every time,” said UCLA gymnastics coach Janelle McDonald, who sat in the front row next to the vault landing area at the U.S. Olympic trials, where Biles competed her signature vault.

Of the five skills in the International Gymnastics Federation (FIG) code of points named after Biles, her most recent vault — the Yurchenko double pike — has become the most iconic.

It’s the first major leap in vault innovation for women’s artistic gymnastics in two decades. When leveling up the sky-high event used to mean extra twists, Biles flipped the game upside down. She was the first woman to attempt her double-flipping skill in competition and completed it in international competition for the first time at the 2023 World Championships, earning its name as the Biles II.

“Simone made impossible an opinion with that vault,” NBC analyst John Roethlisberger said on the telecast during the U.S. Olympic trials.

In a sport that blends power and grace, Biles’ Yurchenko double pike is at the center of its own Venn diagram: athletic feat, scientific marvel and artistic genius all in six seconds.

The entry

The height, the rotation and the landing earn the most gasps from the fans who follow Biles’ every move on the competition floor. But for her peers who continue to marvel at the 27-year-old’s revolutionary talent, the most impressive part of the vault happens before Biles even contacts the table.

“Your Yurchenko entry has to be so technically perfect and so consistent,” said 2016 Olympic gold medalist Kyla Ross. “You have no doubt coming off the table that you’re going to hit the double pike.”

The Yurchenko entry — a roundoff onto the springboard and a back handspring onto the vault table — is named after former Russian gymnast Natalia Yurchenko, who debuted her eponymous skill in 1982. Since the FIG replaced the vault horse — which resembled a pommel horse without handles and was about 5 feet long and 1 foot wide at the top — for a tongue-shaped vault table in 2001, the Yurchenko vault has become more common for elite female gymnasts. Athletes can still harness the power generated from the unique entry while having a larger, safer surface area for their hands.

2024 Paris Summer Olympic Games

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Biles begins with a sprint down the runway and reaches her hands toward the ground while cartwheeling her legs over her head. The roundoff turns her momentum forward to backward. Slamming her feet down on the springboard, Biles compresses the springs that then uncoil and transfer energy back into her body as she reaches up and backward for the vault table.

The key to vault liftoff is how Biles contacts the equipment to transfer her momentum.

“Pre-springboard, all of their motion is forwards,” said Emily Kuhn, a physics PhD student at Yale who was a level 10 gymnast. “After the springboard, some of their motion is upwards. And so [the board is] really helpful for converting the rotational energy from that roundoff into an upwards velocity that is used to get the height on the vault.”

In an instant, Biles arches backward toward the vault table. Her body whips back in a lightning-fast handspring that leaves even the best athletes in the world in the dust.

“She gets that power because of how quick-twitched her roundoff-back handspring is, technically speaking,” said 2008 Olympic silver medalist Samantha Peszek. “No one is as quick-twitch as Simone.”

The block

During the block, the moment Biles’ hands strike the table, she extends through her shoulders in a motion that’s barely detectable in real time. The micro-movement lasts a tenth of a second as Biles applies force to the vault that is then returned in equal and opposite measure.

(Kenzo Tribouillard / AFP via Getty Images)

Aly Raisman had a front-row seat to the world’s best vaulters. The two-time Olympian watched 2012 Olympic teammate McKayla Maroney nail a nearly perfect two-and-a-half twisting Yurchenko in the team final. Raisman was also the team captain in 2016 when Biles won Olympic gold on vault. Both standouts shared a key ability that helped them soar above the competition.

“When you look at her elbows on the table, they’re always very straight,” Raisman said. “Their body was so tight when their arms hit the table that it just helps them get so much air.”

The moment Biles’ hands strike the table, she extends through her shoulders in a motion that’s barely detectable in real time. The micro-movement lasts a tenth of a second as Biles applies force to the vault that is then returned in equal and opposite measure. Keeping every muscle contracted during the split second on the table is vital to transferring energy efficiently for maximum height.

“The force gets dispersed in bad form,” said Gina Pongetti, a physical therapist with more than 20 years of experience working with college, national team and elite gymnasts. “[The muscles] are all tight at one time so that nothing gives, nothing buckles. Because of that, all of that force, or as much as possible, goes into the vault [and] goes back to her to transfer to height and rotation.”

NBC estimated that Biles’ feet reach about 12 feet in the air at the peak of her vault when she is upside down.

Former UCLA gymnast Nia Dennis knows the feeling. The three-time U.S. national team member trained a Yurchenko double tuck — with her knees bent and legs pulled toward her chest — into the foam pit during her elite career, eventually stacking up soft mats to be equal to competition height. While she is best known for her viral, energetic floor routines, Dennis loved vault the most. She still recalls the intoxicating feeling of hitting the perfect block that fired her into the air.

“I just felt like a cannon,” Dennis said.

The flips

After Biles blocks off the vault, she is just a projectile.

(Matthias Hangst / Getty Images)

Searching for ways to upgrade her vault difficulty, Dennis wanted to buck the trend of adding additional twists to her Yurchenko. She was always more of a flipper than a twister, and Dennis sometimes landed on her neck from over-rotating her warm-up drills. One day, her coach encouraged her to pull all the way around onto her feet for an additional flip.

“It was just straight power,” Dennis said. “All I had to do was run and close my eyes, for real. Just block really hard, close my eyes really hard and pull really hard.”

For Dennis, the daring skill was fun. Her former UCLA teammate Ross did not share the sentiment.

“I used to like, cry because I was so scared of it,” laughed Ross, who practiced Yurchenko double tucks into the foam pit alongside her longtime club teammate Maroney.

The second flip is what makes the vault so frightening for athletes. Gymnasts can adjust a twisting vault midair by reducing the number of revolutions by halves if they feel something gone awry. There is no safe Plan B between one and two flips.

After Biles blocks off the vault, she is just a projectile, Kuhn emphasized. At that point, there is nothing she can do to change how high she is or her path through the air.

That’s when her proprioception takes over. Biles’ air awareness is “unbelievable,” Pongetti said. The physical therapist, who specializes in treatment, diagnoses and biomechanics in gymnastics, has watched Biles train for years.

While she cannot change her flight path, Biles is an expert in making split-second decisions to rearrange her body midair to change how she will move. If she is too low, she can pull her body into a tighter shape to flip faster. If she is too high, she knows a more open shape can slow down her flip and help avoid over-rotation.

Only that caliber of spatial awareness can make the death-defying skill “safer,” Pongetti said. She would never say it’s “safe.”

“That sets apart the level 10 [gymnast] from the elite,” Pongetti said, “from the Olympian from Simone.”

The landing

Simone Biles of the United States reacts after performing a vault during the 2023 gymnastics world championships in Antwerp, Belgium.

(Tim Clayton / Corbis via Getty Images)

With five skills named for her in the code of points, Biles is at the forefront of the sport’s progression. Peszek remembers when the double-twisting, double back tucks she and 2008 Olympic teammate Shawn Johnson competed were arguably the hardest tumbling passes in the world. Now Biles casually does that skill in combination with a full-twisting front layout.

“It’s really special to see the generations pass the torch and just how they’ve been able to take this sport by storm by creating all these new elements and really pushing the boundaries,” Peszek said. “Seeing her do it so effortlessly, it’s really a work of art to see.”

The Biles II was awarded the highest-difficulty score of any vault by the FIG at 6.4. Astronomical-difficulty scores, which are combined on each event with an execution score out of 10, allow Biles to win competitions by whole numbers as most of her peers fight for half-tenths.

On vault, most of the top medal contenders have difficulty values of 5.4 for the two-and-a-half twisting Yurchenko known as an Amanar or 5.6 for a Cheng, which begins with a roundoff onto the springboard, a half turn onto the vault table and a one-and-a-half twist off.

But Rebeca Andrade could challenge Biles for the crown. The Brazilian Olympic confederation published a YouTube video that featured the Olympic and world vault champion training a triple-twisting Yurchenko. If she lands it in international competition, it will bear her name.

Biles considered the skill as the next Yurchenko progression from an Amanar but has said going for the double flip was safer for her to land. The landing on a twisting flip presents additional challenges, Kuhn said, as gymnasts must absorb rotational forces to stop the twist while also controlling the landing vertically.

A 2013 study estimated that gymnasts absorb 11 times their body weight on landings during competition. The force increases to 18 times body weight if a landing is uneven, a common consequence of twisting elements. What Biles feels when her 4-foot-8 frame is falling from more than two and a half times her height to land the Yurchenko double pike might be even greater, Pongetti said.

“Her quads and her glutes and her hamstrings [and her calves], which otherwise would work to allow her to jump high, work in reverse to slow her down,” Pongetti said. “They are her brakes. … She is so good at not being stiff-legged when she lands.”

Fans seem to hold their breath as Biles floats and flips through the air. At the moment her feet punch into the mat, the crowd exhales with a roar of applause.

Thousands in Paris’ Bercy Arena will see the vault’s official Olympic debut. Millions more will watch internationally.

They’ll see Biles push the boundaries of sport and science in a gravity-defying six-second burst.

From morning to evening, six days a week, Gustavo Reyes Gonzalez spent his days cutting engineered stone, a man-made product that has become a popular choice for kitchen and bathroom countertops.

The glossy slabs resist stains, are highly durable and come in many colors. They are also rife with crystalline silica: tiny particles that can irreparably scar the lungs when inhaled.

By the time Reyes Gonzalez had reached his 33rd birthday, his lungs had been ravaged by silicosis, an incurable disease. He was forced to rely on an oxygen tank and grew thin and weak. At one point, he said, he asked God to take his life so that his suffering would end.

His doctor says the 34-year-old is only alive today because both his lungs were replaced in a transplant — and that painstaking surgery may only buy him another six years.

“We don’t know how long he has with that lung,” his wife Wendy Torres Hernandez said in a Los Angeles courtroom. In the wake of his transplant, he must take a barrage of medications, restrict his diet and keep a close eye on his blood pressure and sugar levels.

All of those measures, she said, are “going to continue until he passes away.”

In Los Angeles County, a jury will weigh a question that could reverberate through the stone industry: Are corporations that manufacture or distribute engineered stone at fault?

Health researchers have tied the surge in silicosis cases among countertop cutters to the booming popularity of engineered or artificial stone, which is typically much higher in silica than natural marble or granite. In California, dozens of workers with silicosis have lodged lawsuits against companies like Cambria and Caesarstone.

Reyes Gonzalez is the first of them to go to trial, according to his attorneys. The L.A. County civil case poses a test of whether companies that make engineered stone could be held responsible amid the devastating eruption of silicosis, which has killed more than a dozen countertop cutters across California in recent years.

Dr. Robert Harrison, a professor of occupational medicine at UC San Francisco who has done research on silicosis among countertop cutters, said a decision for the plaintiff would “send a message to manufacturers that they are accountable for producing a toxic product like engineered stone.”

Regardless of the outcome, Harrison said the court case “shines a spotlight on the workers behind the products that we buy.” That could bolster public awareness that “there are workers who make our products who get sick and die,” he said — and hopefully inspire new efforts to stop it.

Marissa Bankert, executive director of the International Surface Fabricators Assn., which represents businesses that cut slabs, said that “irrespective of the outcome of this case, it is essential that all companies engaged in surface fabrication and their employees are educated on, and adhere to, safety practices.”

In a trial that has stretched for weeks, lawyers for Reyes Gonzalez have argued that engineered stone manufacturers failed to give proper warnings about the dangers of their product. Attorney Gilbert Purcell called it “terribly toxic and dangerous” and “defective in design,” arguing that its risks far outweigh its benefits.

The question is, “why not eliminate this product altogether? Society doesn’t need this product,” Purcell told jurors. “It certainly doesn’t need the carnage it causes.”

Attorneys for engineered stone manufacturers countered that the blame lay with the operators of the Orange County workshops where Reyes Gonzalez worked. Such “fabrication shops” cut the slabs made by manufacturers.

“We know that this product is safe,” Cambria‘s attorney, Lindsay Weiss, said, “when handled safely.”

Reyes Gonzalez testified that he worked in a string of Orange County shops cutting slabs of engineered stone. At times, he said, the air was so dusty that it looked like fog. His mask grew “very filthy,” he testified. Even when he used water while cutting, Reyes Gonzalez said that after it dried, “a lot of dust would come off.”

Caesarstone argued in court that the company had given the shops all the information they needed to protect workers, including guidance on ventilation and wet cutting to tamp down dust. Its attorney, Peter Strotz, said what happened to the worker was a tragedy, but a preventable one.

It could have been prevented if those “who owned and operated the fabrication shop where he worked had done what Caesarstone asked them to do,” Strotz argued.

He and other attorneys representing engineered stone manufacturers sought to turn the focus to members of the Silverio family, who had paid Reyes Gonzalez for his work at the Orange County shops.

Lawyers for the worker argued the Silverios were not his employers and that Reyes Gonzalez was an independent contractor. Fernando Silverio Soto, who set up Silverio Stone Works, testified that all he knew about the dangers was what he was told: To minimize risk by wearing masks and using water while cutting.

Strotz showed the courtroom a Caesarstone form that Silverio had signed, which stated he had received safety information and an instructional movie. In court, Silverio denied having seen such materials.

Jon Grzeskowiak, Cambria’s executive vice president of research and development and process operations, said the company offers free training to stonecutters and that safety information for its products was available on its website. Fernando Silverio Soto said during his testimony that he hadn’t seen that website, nor had he gone to the Caesarstone website for such information.

“I was never told that I needed to do that,” he said of the Caesarstone website.

Defense attorneys also brought forward expert witnesses who testified that engineered stone could be cut and polished safely with the effective use of workplace safeguards. Attorneys for Reyes Gonzalez, in turn, turned to experts who disputed that measures such as masks or using water while cutting were adequate.

Among them was industrial hygienist Stephen Petty, who testified that an N95 mask was insufficient to protect a worker from the dust generated by grinding artificial stone.

Petty said even the best kind of respirator available, which supplies a worker with clean air from a tank, would not work well in the long term because it is so uncomfortable that workers tend to adjust it, breaking the seal.

Harrison of UCSF, who did not testify in the case, said it is very difficult to protect workers cutting engineered stone. “It takes a lot of money and a pretty sophisticated, knowledgeable employer with a lot of expensive machines and ventilation systems to protect workers from exposure to artificial stone dust.”

Safety regulators across the globe have grappled with the risks of engineered stone as its popularity has soared. In Australia, the government ultimately banned the artificial slabs amid a public uproar over stonecutters falling ill and dying. Workplace safety regulators there called it “the only way to ensure that another generation of Australian workers do not contract silicosis from such work.”

In California, government regulators have stopped short of a ban, instead enacting tighter rules on silica exposure in the workplace. Another proposal that would have clamped down on which businesses could perform stonecutting was held this summer by its author, Assemblymember Luz Rivas (D-North Hollywood), who said state regulators were “not receptive” to creating a tracking system for licensed shops.

Cal/OSHA officials have warned in the past that if tightening the rules does not show results, they could press forward with a ban on engineered stone. In a recent report, however, the agency said it had so far rejected the idea because a ban could fuel “the creation of illegal fabrication shops that are hidden from regulators.”