Tuesday, October 3, 2023

The real secret why knee arthritis is getting prevalent

The incidence of knee arthritis has doubled in the last 75 years. But it is not because of increased obesity, longer lifespans, or people running for recreation. An ingenious study points to the cause: our modern, sedentary lifestyle.

Executive Summary

Knee arthritis has more than doubled in the last 75 years. But why?

There may be multiple reasons:
• Increased incidence of obesity, which is linked to arthritis.
• Increased lifespans, since arthritis is mainly an old age disease.
• Running, as a new recreation, maybe damage the knees.

But, researchers at Harvard University found that none of the above to be the reason.

They analysed ancient and modern skeletons. They found that knee arthritis has doubled in modern people compared to those 75 years ago, even for the same age and level of obesity (BMI).

Their best guess for the culprit: our inactive lifestyles.

The cartilage is a living tissue, which strengthens on usage. Our modern, sedentary lifestyle is leading to thinner, lower-quality cartilage in the joints and weakness in the muscles that would otherwise take some load off those joints.

Read the full article for the macabre but brilliant research.

Knee arthritis has more than doubled in the last 75 years. But why?

Why should knee arthritis become more prevalent?

People say that it is because of increased obesity and longer lifespans. Sounds logical, right?

Increased obesity

Obesity has increased significantly in the last few decades. It is so common now that it is considered an epidemic.

Obesity has been found to be linked to increased osteoarthritis risk. We don’t know the exact reason, but the main culprit may be inflammation. Obesity is an inflammatory disease. And, so is osteoarthritis. Perhaps, that is the linkage.

Read on this website: Why obesity worsens knee osteoarthritis?

Increased lifespan

Thanks to improved medical care, people are living longer. In developed countries, the average life expectancy has shot up.

As you age, there are certain degenerative changes in the matrix of the knee cartilage. The cartilage starts breaking down, leading to some signs of osteoarthritis. By the time someone approaches the age of 65 years, 75% chance that he will be showing at least a few minor signs of osteoarthritis.


One more logical culprit is running. The fad of running for recreation has been quite prevalent in the last 55–60 years. Running also is considered a cause of osteoarthritis. Since no one ran for recreation 75 years ago, running also seems to be one potential reason for the increase in incidence.

Of course, you can read of this website, a comprehensive article: Everything you want to know about running and osteoarthritis. This extremely detailed article considers dozens of studies done on various aspects of running and osteoarthritis and shows that running does not cause osteoarthritis. In fact, it reduces the chances of getting osteoarthritis.

The study

Researchers at Harvard University did some ingenious, and extremely macabre, work to debunk this hypothesis. They published a paper in 2017 in the journal Proceedings of the National Academy of Sciences of the USA about their findings.

The researchers analysed ancient and modern skeletons. They found that knee arthritis in the last 75 years has doubled compared to earlier times, even for people of the same age and level of obesity (BMI).

In other words, if you take two persons of the same age, from today as well as from 75 years ago, the chances that today’s living person has osteoarthritis are double that of the person who lived 75 years ago. Of course, this is seen on an average, over many such people.

Ditto for obesity. If you take two people of the same BMI, which is a good measure of obesity, the modern counterpart is twice as likely to have osteoarthritis as his ancient counterpart.

Once you get over the yucky part about traveling from cemetery to cemetery all over the USA, exhuming skeletons after skeletons, and studying them, you will realise how ingenious this was. After all, no one had the data from 75 years ago, about osteoarthritis, BMI, and age. Of course, they must have had some data, but not of the same people. Who would thought in 1942 that someone would do such a trial in 2017?

The scientists can look at the ends of the bones in a knee joint of a skeleton and know if the person had arthritis. The bone endplates show a different type of wear and tear if the person died with osteoarthritis.

Similarly, forensic scientists can estimate the height and weight of a dead person from his skeleton. So the BMI of the ancient person can be calculated, and his obesity can be roughly estimated.

The culprit

They had three guesses for the culprit. It is not running, obesity, or increased lifespan.

  • Guess 1: Hard, paved surfaces. Walking on modern, hard surfaces caused knee damage.
  • Guess 2: High–heeled shoes. They found women were 50% more likely to have knee arthritis than men.
    I have personal doubts on this one though: India is the knee arthritis capital of the world, with an arthritic person in nearly every extended family. And, almost no conservative woman wears high–heeled shoes. My mother and aunt never wore anything with high heels. And, they both had knee arthritis. And I know thousands of such arthritis cases of senior ladies from conservative families.
  • Guess 3: Their strongest guess is inactivity. Our sedentary lifestyle of the modern times is leading us to osteoarthritis.
    The joint cartilage is like our bones. The more we use it, the stronger it gets. Our inactive lifestyle is making our cartilages atrophy, leading to knee osteoarthritis.

Read in simple English: Knee arthritis has doubled… and it is not because of running.

In conclusion

Knee cartilage does not seem to follow the wear-and-tear model. It is a living tissue, which improves with the added workload.

Physical inactivity seems to be the reason for the nearly double prevalence of knee arthritis.

If one sits at a desk all day, one ends up with thinner, lower-quality cartilage in the joints, and weakness in the muscles that would otherwise take some of the load off those joints.

First published on: 18th August 2017
Image credit: JESHOOTS.com from Pexels
Last Updated on: 17th December 2021


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