People in most of the world have gotten significantly taller in the past century. 

A network of health scientists known as the Non-Communicable Diseases Risk Factor Collaboration (NCD-RisC), released a study ranking height around the world for men and women. The study looked at height differences for 18-year-olds born in 1896 versus 1996 in 187 countries. 

Lead scientist Majid Ezzati told BBC News that while some of these changes can be explained by genes, "variations across the world are largely environmental." That means people are getting taller because of better healthcare, sanitation, and nutrition.

Topping the list, women in South Korea have grown an average of 9 inches taller and men in Iran have grown an average of 6 inches taller.

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In a global height analysis based on nearly 1,500 studies, Dutch men and Latvian women topped the charts, standing tallest at heights of 182.5cm and 169.8cm on average respectively.

The study found heights have changed dramatically between 1914 and 2014, with South Korean women showing the largest increase of 20.2 cm over the period.

Americans are leading the race in another trend: plateauing.

The study shows that although humans as a species are still getting taller, countries such as the US, UK, and Japan have stopped or slowed growing significantly in the last 30-40 years.

The US, once home to the 3 tallest men and 4 tallest women in the world, are now sitting in 37 and 42nd place respectively.

"This study gives us a picture of the health of nations over the past century, and reveals the average height of some nations may even be shrinking while others continue to grow taller," said lead researcher Ma jid Ezz ati from Imperial College London in the UK.

"Our study also shows the English-speaking world, especially the USA, is falling behind other high-income nations in Europe and Asia Pacific. Together with the poor performance of these countries in terms of obesity, this emphasis es the need for more effective policies towards healthy nutrition throughout life."

Although part of the height difference can be attributed to genetics, the height increase is likely due to nutrition, hygiene, and healthcare – factors that influence whether people are reaching their height potential.

"An individual’s genetics has a big influence on [their] height ... but once you average over whole populations, genetics plays a less key [role]," one of the researchers, James Bentham, told Nicola Davis at The Guardian.

"Most populations would grow to roughly similar heights if they were all in the same conditions."

So where does your country sit in regards to heights, then and now?

The researchers have put together an interactive world map to show how our heights have changed.

There’s also a full list of rankings for males and females in the 200 countries studied.

Most of the top countries for height are European countries, with Australia being the only country not in Europe to be inside the top 25.

The news isn’t all good – some countries, particularly those in sub-Saharan Africa, North Africa, and the Middle East, have seen a decline in the average height in the last 30-40 years.

"This confirms we urgently need to address children and adolescents' environment and nutrition on a global scale, and ensure we're giving the world's children the best possible start in life," said Ezz ati.

The study gives an interesting insight into how we have changed over the last 100 years – a time before teenager was a word, over half the US population lived in rural areas, and modern medicine was just getting off the ground.

"This is a unique analysis that shows the real power of combining a hundred years of population data sources that span the globe," said Mary De Silva from the Wellcome Trust, who wasn’t involved in the study.

"The most striking finding is that despite the huge increases in height seen in some countries, there is still a considerable gap between the shortest and tallest countries. More research is needed to understand the reasons for this gap and to help devise ways of reducing the disparities in health that still persist globally."

The study was published in eLife.

SEE ALSO: How people get tall

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It's difficult to tell how tall a movie or TV star actually is from just seeing them on the big screen.

In the past, we've given you a look at some of the shortest stars in Hollywood.

Now here are the ones who rise above the others.

Model Brooke Shields is an even 6 feet tall, and 6-foot-5 Vince Vaughn tends to tower over his costars.

See some of the tallest celebrities in Hollywood below.

Note: Christina Austin contributed to this story.

SEE ALSO: 20 of Hollywood's shortest celebrities

At 5-foot-10, Charlize Theron looks much taller than 5-foot-8 Sean Penn.

5-foot-10 Blake Lively towers over Woody Allen and her castmates from Allen's "Cafe Society."

Khloe Kardashian's 5-foot-10 stature makes her significantly taller than sisters Kim and Kourtney, who barely break 5 feet.

Disclaimer: Do not attempt to try this.

Skateboarder Cheung Jai has taken his love of heights to a scarily new level.

One of his latest videos shows him balancing his skateboard on a rusty railing on top of a Hong Kong skyscraper.

He's gained a lot of attention on Instagram, with people either praising his bravery or criticising him.

Produced by Claudia Romeo

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Americans used to be among the tallest people in the world, but stopped growing taller around 1960.

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A successful politician needs a few things: good ideas, a strong voter base, and above-average height.

In any competitive environment where opinions and egos clash — as they often do in politics — an inch or two of height is no small advantage. Keeping that in mind, it's understandable that a politician would want to wear boots or other slightly heeled shoes to appear taller.

There's more to this desire to appear taller than just ego, however. Sociological studies and historical evidence have shown that taller men often enjoy more social success, partly because others tend to have a more positive perception of them.

"We conclude that human height is positively related to interpersonal dominance, and may well contribute to the widely observed positive association between height and social status," write the authors of one peer-reviewed study that was published in 2015 by the University of Groningen in the Netherlands.

According to The New York Times, the taller of the two major candidates has won the US presidential election twice as often as the shorter candidate. 

And all this time you thought Texas politicians wore cowboy boots just for their folksy charm.

Politicians from Florida Senator Marco Rubio to Russian President Vladimir Putin have visibly employed the heeled-shoe technique. It's difficult to pin down a man's actual height after all, as there is often a discrepancy between the official statement of a leader's height and how tall they stand in real life.

There was some speculation that Canadian Prime Minister Justin Trudeau's shoes had lifts during his visit to the White House this week, as the 6'2" PM appeared to be at eye level with the 6'3" President Trump. There is some debate about Trump's height, as Politico obtained one of his old driver's licenses that listed his height as 6'2".

It's safe to say that other politicians, especially if they're on the shorter side, would want to exaggerate their height in a similar way.

Taking the Florida senator as another example: Rubio's height is listed as 5'10" on official documents, though it's rumored he's closer to 5'8". At his unofficial height, Rubio would've been the shortest president since William McKinley, who stood at 5'7". So it's no surprise that he was caught with some wickedly heeled boots when he was running for president, though he was mercilesslymocked for the shoe choice.

Even if it is a politician's goal to be a man of the people, there seem to be plenty of reasons to strap on some stacked heel boots.

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Dave Coleman is an arborist based in Australia. He fells trees at incredible heights – usually at around 70 metres.

He rigs ropes to the trunks and branches to make sure they don't hit houses when they fall to the ground.

All the trees are in the Dandenong Ranges in Victoria. Some of those, the Eucalyptus Regnans, are the tallest in Australia.

Produced by Claudia Romeo

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People in most of the world have gotten significantly taller over the last century.

A network of health scientists known as the Non-Communicable Diseases Risk Factor Collaboration (NCD-RisC), published a study in the journal eLife in 2016 that analyzed height changes around the world. The team compared 18-year-old men and women born in 1896 to those born in 1996 in 187 countries. 

Lead scientist Majid Ezzati told BBC News that while some of these changes can be explained by genes, "variations across the world are largely environmental." That means people are getting taller due to external factors like better healthcare, sanitation, and nutrition.

Topping the list, women in South Korea grew an average of 9 inches taller and men in Iran grew an average of 6 inches taller. Here's the breakdown:

SEE ALSO: This gif shows all of the US presidents in order of height

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Humans have grown dramatically taller over recent years. This video shows the countries where people have grown the most in the past 100 years.

Original Reporting by Skye Gould

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The Ledge is a glass box on the 103rd floor of the Willis Tower, the eighth-tallest building in the world and the tallest building in the Western hemisphere. At an altitude of 1,353 feet you can see up to 50 miles and four states. The Ledge attracts more than 1.7 million visitors annually.

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It's often difficult to tell how tall a celebrity is, but you can easily tell when there's a drastic difference.

Some celebrity couples make that difference pretty clear. 

Here are 25 celebrity couples with some extreme height differences. 

At 5' 4", Mila Kunis is much shorter than her 6' 2" husband, Ashton Kutcher.

Kristen Bell is a petite 5' 1" standing next to her husband Dax Shepard, who is more than a foot taller at 6' 2".

Will Smith stands 14 inches above his 5' 0" wife Jada Pinkett Smith at 6'2".

• Meghan Markle's height has become one of the most searched for facts about the soon-to-be-royal, especially in comparison to Kate Middleton.
• Markle is reportedly 5'7", while Middleton is a slightly taller 5'9".
• Prince Harry is 6' 1" while Prince William is 6'3", meaning both couples have a six-inch height difference between them.

When Meghan Markle shot to superstardom after her engagement to Prince Harry, everyone quickly wanted to know everything about the soon-to-be-royal. While people have dug up everything from her childhood videos to her appearance in an incredible Tostitos commercial, there's one thing people can't seem to definitively figure out: her height. 

A quick Google search reveals that Markle is 5'7", though some outlets have reported that she's actually 5'6". However, most people seem to agree that 5'7" seems more likely when compared to Kate Middleton, who is slightly taller at 5'9".

Here's a photo of Markle and Middleton standing together in similar heels, with Middleton appearing to stand two inches above Markle.

Here they are again, with the same apparent height difference. 

Their height difference can also be spotted by looking at photos of them standing next to the royal men in their lives: Prince Harry and Prince William.

For example, Prince Harry is 6'1" , and Middleton is only four inches shorter.

He might not be much taller than his sister-in-law, but he does appear to have about six inches on his fiancé. 

Prince William, on the other hand, is an even taller 6'3", which means both royal couples have the same six-inch height difference between them.

Although he has six inches on Middleton, William is a whopping eight inches taller than Markle.

We'll possibly get a chance to compare their heights even further when they attend the highly-anticipated royal wedding on May 19.

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While every American president and first lady has reached the same heights of political office and public service, not all reached the White House at the same physical height.

The average height of US presidents was 5-foot-10-inches, and the typical height difference between presidents and first ladies was 6.5 inches.

Scientific studies suggest that men have it better when it comes to success in the workplace, and that women are more likely to choose taller men than shorter men.

John Adams and Abigail Adams were only separated in height by an inch, while Thomas Jefferson was over a foot taller than his wife Martha Jefferson.

We found the heights through online research and speaking with presidential historical sites and libraries. But a few first ladies' heights have been lost to history.

Here is the height difference of every US president and first lady we could find:

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George and Martha Washington: 1-foot-2-inches (36 cm)

John and Abigail Adams: 1 inch (2 cm)

Thomas and Martha Jefferson: 1-foot-2.5-inches (37 cm)

Jefferson was a widower when his presidency began, and his daughter, Martha, acted as first lady, along with wives of the Cabinet secretaries.

• Cats famously land on their feet when they jump off furniture and trees, but they use a different technique to survive falls from much greater heights.
• Some cats have walked away from falling as high as 32 stories with limited injuries.
• Watch the video above to learn the amazing technique cats use to catch their fall.

Following is a transcript of the video.

32 stories above the streets of New York City, a cat fell from a window and lived. After vets treated the cat's chipped tooth and collapsed lungs, the feline was sent home two days later.

Cats fall a lot, and they've gotten really good at it. Drop a cat upside down, for example, and it will almost always land on its feet. That's because cats are extremely flexible. They can twist their bodies mid-air as they fall.

But landing feet first isn't always the best strategy. Like if you're falling from 32 stories up. To figure out how cats manage that perfect landing every time, a series of studies looked at over a 100 cats' falls from two to 32 stories up.

Comes as no surprise that cats who fell from the second floor had fewer injuries than cats who fell from the sixth floor. But here is the fascinating part. Above the seventh story, the extent of the injuries largely stayed the same, no matter how high the cats fell. So, how is that possible?

Well, it all comes down to acrobatics or lack thereof. Cats that fell from two to seven stories up mostly landed feet first. Above that, however, cats used a different technique. Instead of positioning their legs straight down as they fell, they splayed out like a parachuter. And landed belly-first instead.

But this method isn't 100% foolproof. Chest trauma, like a collapsed lung, or broken rib is more common with this landing method. But the risk of breaking a leg is much less. So, how do cats somehow subconsciously know how to land?

It has to do with a physics phenomenon called terminal velocity. At first, the cat plummets faster and faster under gravity until she's fallen the equivalent of five stories. At that point, she hits constant terminal velocity at 100 kilometers per hour. She's now in free fall where air friction counteracts her acceleration under gravity. At this point, she's no longer accelerating and, more importantly, doesn't feel the pull from gravity.

So, here's what researchers think is happening. From two to seven stories up, cats don't have enough time to reach terminal velocity and prep for landing feet first. But once they hit terminal velocity, their instinct changes and they parachute their limbs.

All that said, don't throw your cat out of a window. I can't believe I have to say this. Not only is it still very dangerous, it's not very polite. Don't throw your cat out the window just to see all that go down. Just watch this video again. Just hit the little replay button.

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• "Jack Reacher" is getting a small-screen reboot.
• Tom Cruise, who plays the eponymous hero in two films ("Jack Reacher" and "Jack Reacher: Never Go Back"), has already been ruled out from the TV series because he is too short.
• In the original books by Lee Child, Reacher is described as having hands like "Thanksgiving turkeys" and is 6-foot-7, while Cruise is around 5-foot-7.
• Child told BBC Radio Manchester: "Cruise, for all his talent, didn't have that physicality."

Jack Reacher has already had two movie outings thanks to Tom Cruise, but the character is being rebooted in a new TV series, as the 56-year-old actor was too small.

The character of Jack is an ex-US Army military police officer who leaves to investigate suspicious crimes, and is often depicted in the books as being huge.

Jack's hands have been described as "Thanksgiving turkeys" or "supermarket chickens" in the books, with a height of 6'7", while Cruise himself is reported to be around 5'7".

Speaking to BBC Radio Manchester, Jack Reacher creator Lee Child said: "Cruise, for all his talent, didn't have that physicality.

"We're going to take it to Netflix or something like that. Long-form streaming television, with a completely new actor.

"And I want all those readers who were upset about Tom Cruise to help me out — participate in choosing the right actor for the TV series.

"We're rebooting and starting over and we're going to try and find the perfect guy."

The TV reboot was previously confirmed back in August, with Child telling The Guardian: "I've got tens of thousands of letters saying they didn't like Cruise because he's too small, basically. Part of Reacher's appeal is that he's very intimidating.

"Even without doing anything, if he walks into a room, people are a little bit uneasy. It was felt that, for all his virtues, Cruise didn't represent that. So the readers were cross from the beginning."

He added: "That's the great thing about television. It's much less star-driven than feature films. So it doesn't need to be a so-called A-list guy."

There are 22 Jack Reacher novels in total, so plenty of material for a potential TV show to adapt. It's thought that each season would devote around 10-12 hours to each book.

So who could play such a tall — but affordable — TV version of Jack Reacher? Well, Aquaman's Jason Momoa stands at 6'3", while Armie Hammer is 6'5".

However, Dwayne 'The Rock' Johnson (who is 6'5", height fans), previously revealed he went for the role before Tom Cruise landed it.

MORE FROM DIGITAL SPY:

• Jack Reacher is heading to TV — but who is he?
• Jack Reacher novels are coming to TV
• The further Tom Cruise runs, the better his films are
• Mission: Impossible — Fallout reviews are outstanding
• 10 of the weirdest movie casting decisions ever

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• The stylist that has worked with the Haim sisters and Noah Cyrus has some tips for how to dress taller. 
• She recommends avoiding cropped pants and jackets and instead opting for long, flared pants and longline blazers. 
• When it comes to shoes, pointed-toe pumps are best. 

If you're looking to appear taller, it's all about visually creating a smooth, unbroken line from your head to your toes, said stylist Mecca Cox, who has worked with the Haim sisters, Noah Cyrus, and Shannon Purser, as well as men like Wilmer Valderrama and The Backstreet Boys. In other words, certain pants styles, shoes, and even jackets can "cut you off," while others help elongate your body, mostly due to proportion.

So what are some clothes that the petite crowd should steer clear of? What should they embrace? Cox — who also noted that, of course, there isn't anything wrong with being short and looking short — shared a few great tips, ahead.

Say so long to cropped pants.

While some may assume that cropped pants can make legs look longer, Cox warns against anything flared. "A cropped flare is going to draw your eye out and cuts off your length," she said.

However, this rule doesn't mean all cropped options are a no-no. "If you're going to wear a cropped pant, they should just be straight," she advised, recommending "a high-waisted trouser that cuts off at the ankle, but is a straight leg," instead. "If that runs into an ankle boot, it's still one continuous line."

There are some things to keep in mind when choosing ankle boots.

"A lot of female clients won't want to wear ankle boots because they feel it cuts them off," Cox told INSIDER, adding that she agrees. Still, it mostly depends on the length. "If you get an ankle boot that cuts just below your ankle, it won't cut you off. If it goes above your ankle, it does."

She also said a trick is wearing a boot that is skin tight. "Like a sock boot, or something that zips where the ankle is so that it gives you the contrast from your foot to your ankle."

There's one shoe in particular that always works for shorter women.

A pointed-toe pump is a no-fail option, since "you want something that's going to keep your foot open and elongate the length of your leg."

• The results of President Donald Trump's second physical examination were released on Thursday.
• According to his full health report, Trump is 6 feet 3 inches tall, making him one of the taller presidents.
• The tallest American president was Abraham Lincoln, at 6 feet 4 inches.
• James Madison, the country's fourth president, was the shortest at 5 feet 4 inches.
• In honor of Presidents Day, this animation shows all of the presidents in order of height, from tallest to shortest.

SEE ALSO: Quotes from every president

DON'T MISS: The 34 colleges that produced the most US presidents

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• The world is full of adventures for adrenaline junkies.
• From a Thrill Walk in Switzerland to eating Dinner in the Sky, these are nine thrills for people who aren't afraid of heights.
• Visit INSIDER's homepage for more stories.

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• Some men and a few women are getting plastic surgery to lengthen their limbs and grow up to six inches taller.

• Dr. Kevin Debiparshad, founding surgeon at The LimbplastX Institute in Las Vegas, Nevada, has performed this procedure on more than 30 people since opening his practice in 2018.

• The two-hour, $76,000 procedure involves minor breaks in the leg bones, nails and screws, and physical therapy. It takes a full year to see the end results.
• Some patients may lose some athletic ability, and a psychologist previously told Insider "cosmetic procedures don't have a lasting effect on people's positive body images nor their general well-being."
• Visit Insider's homepage for more.

When you think of plastic surgery, boob jobs and liposuction are likely some of the first procedures to come to mind. But limb-lengthening surgery is now also an option for people who want to be up to six inches taller.

Plastic surgeon Dr. Kevin Debiparshad founded The LimbplastX Institute in Las Vegas, Nevada, in 2018 to create a business centered around limb-lengthening cosmetic surgery. Debiparshad told Insider that since opening The LimbplastX Institute, he's worked with more than 30 people to make them taller.

According to Debiparshad, many patients — surgeons, lawyers, and venture capitalists among them — come to him as "fairly successful people career-wise, but they have feelings of lacking"when it comes to height. 

"They think if they can modify this one complaint, it can make their life complete in some way," Debiparshad said, adding that post-surgery they thank him for making their lives better because they feel less insecure.

Most of Debiparshad's patients have been men, he said, but he's also had some women who want to add height to their appearances.

Limb-extending technology has existed for some time

Although lengthening a person's bones for cosmetic purposes is a new concept, the technology and procedure to do just that had existed for nearly 100 years, according to the journal Children's Orthapaedics.

Today, the procedure involves inserting surgical nails and screws into the hollow part of a person's bone, usually in the legs, and slowly extending the nails and screws to train the tissue in the area to permanently stretch.

This procedure is commonly used on patients with leg wounds from military service, car crashes, or other traumatic events, but Debiparshad said he and his mentor Dr. Dror Paley in West Palm Beach, Florida, began using the technique for cosmetic purposes. 

Debiparshad is the first-known surgeon to open a practice dedicated to making people taller.

The procedure costs $76,000 and requires two hours of surgery and weeks of physical therapy

If a person wants to add height to their appearance, it comes at a cost — $76,000, to be exact.

At Debiparshad's LimbplastX Institute, that price tag includes the surgery itself, hospital stays following the operation, and two to four weeks of physical therapy, which Debiparshad said is a necessary part of the limb-lengthening process. Airfare to Las Vegas, food, and hotel costs aren't included in the $76,000.

When a patient gets "Limbplastx," as Debiparshad's practice calls the procedure, they're first given a general anesthetic so they're asleep for the entire two-hour procedure.

During that time, Debiparshad breaks the bone in the lower leg, thighbone, or shin area by making a half-inch incision in the skin and then using a small drill to weaken the bone and help it to break in a precise area. Then Debiparshad penetrates the bone with a chiseling tool that's also commonly used in nose job procedures.

Finally, he inserts nails and screws to repair the small break he created. He does this on each leg. 

Following surgery, the patient stays in the hospital for one night for basic monitoring and to receive pain medication, blood thinners to prevent blood clots, and muscle relaxers, Debiparshad said.

Each patient is also given an iPad and given instructions to press a button on the device daily, which sends a signal to the implants Debiparshad installed earlier to extend about one millimeter each day. After 25 days of pressing the button, a person will have gained about an inch of extra height, according to Debiparshad.

"Tricking the body into thinking you're growing is basically what this is," Debiparshad said.

After one week recovering, patients can start to walk regularly again and go to physical therapy, which Debiparshad said is necessary to stretch the tissue connected to the bones and help patients regain their full range of motion.

They continue with physical therapy until they've reached their desired height, which can be up to five or six inches taller than their height before the procedure. A year later, Debiparshad removes the screws and nails and the bone and tissue stay permanently stretched from that point forward.

According to Debiparshad, the procedure can cause pain especially during the first week of recovery since it does involve the breaking of bone, but most patients tell him the pain wasn't as bad as they expected it to be. Most patients can walk around the medical facility where they're recovering just a day after surgery.

You could lose some athletic ability following surgery

Debiparshad said his Limbplastx procedure also comes with minimal risks outside of those typical for any surgery, like blood clots and pneumonia, because the technique has been used for decades.

Patients who are able to run very quickly could be affected though, because the procedure changes a person's stature.

"You may trade off some athletic ability to get to that end stage," Debiparshad said. "You can walk and go to the gym, but you might not be able to sprint 100 meters in nine seconds," if that's something you could do before surgery.

He believes the technique has the potential to become mainstream like breast augmentations and Botox, two popular cosmetic offerings.

Still, cosmetic surgery isn't a cure-all for feeling physically inadequate, health psychologist Charlotte Markey previously told Insider.

"Self-acceptance is not just about how we look," she said. "Data suggests that cosmetic procedures don't have a lasting effect on people's positive body images nor their general well-being."

Read more:

• People think surgically altered labia look more 'normal,' but there's no such thing as normal-looking labia
• People are paying $5,500 for temporary butt and breast injections to look more like celebrities on Halloween, according to a plastic surgeon
• The 'human Ken doll' has spent more than $750,000 on 72 cosmetic surgeries, and doctors warn that his addiction has gotten dangerous

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