Chapter 112
Sport
Even if we lose about a pound a year for ten years, this can reduce the likelihood of developing osteoarthritis by more than 50 percent. MRI studies show that in overweight people who already suffer from cartilage wear, even a weight loss of 5 percent can significantly reduce the extent of wear. As I explain in see.nf/kneereplacement, the knees of randomized obese osteoarthritis patients functioned just as much better after they lost weight as those of people who underwent surgery—and that after only eight weeks. The researchers concluded that ten kilos less fat could be considered “as an alternative to knee replacement.”
This is especially important when you consider that almost 1 in 200 people who get a new knee is dead three months after the operation. In the United States, about 700 000 such operations are performed every year. On the general popularity of this procedure, an editor of an orthopedic specialty journal wrote: “People considering this surgery are inadequately prepared for the fact that they could die from it.”
Exercise
Smokers tend to be leaner than nonsmokers, which may explain why some studies found an association between smoking and protection from osteoarthritis. Smokers with osteoarthritis usually have more severe pain and greater cartilage loss than nonsmokers. Another possible explanation for the lower osteoarthritis rates among smokers is, ironically, that they are less likely to exercise.
Knee sports injuries are a recognized risk factor for osteoarthritis later in life. At the same time, physical inactivity can endanger the knees—not only because weakened muscles lead to less stable joints, but also because cartilage degenerates if you don’t use it. In people with paralyzed legs, the cartilage in the knees becomes significantly thinner over time, whereas people who train with heavy weights tend to have thicker cartilage. Both extreme inactivity and extreme activity can be harmful.
Is exercise a treatment option? There have been four dozen randomized controlled trials with thousands of patients on treating knee osteoarthritis with exercise. Exercise consistently reduced pain, to such an extent that some researchers felt further studies on the topic were unnecessary. Direct comparisons of aerobic and resistance training showed that intensity didn’t matter, but frequency did. The most effective were training programs with at least three sessions per week and those that focused on the quadriceps. Although most studies were short-term, there were some that demonstrated clinically significant improvements after at least one year, without reports of impairment. National and international guidelines for the treatment of osteoarthritis emphasize the importance of weight loss and exercise. And what about diet?
Diet
To treat osteoarthritis as effectively as possible, one should consider “optimal nutrition” from the start. As the best example of this, reviewers in the journal Arthritis cite the “China study,” shorthand for the China-Cornell-Oxford Project, shorthand for “China-Oxford-Cornell Study on Dietary, Lifestyle and Disease Mortality Characteristics in 65 Rural Chinese Counties,” a large study that its director T. Colin Campbell—the same Dr. Campbell who coined the term whole-food, plant-based diet—and his son summarized in the popular-science book The China Study. What evidence is there that a plant-based diet could help?
The National Institutes of Health Osteoarthritis Initiative, the largest prospective study to date of osteoarthritis patients, found that higher fat intake accelerates progression of the disease (cartilage loss was visible on X-rays). On further analysis, however, it turned out that only saturated fats increase risk. This is the type of fat found primarily in meat, dairy products, and junk food, not the mono- or polyunsaturated fats in nuts, seeds, and plant oils. Even dripping saturated fat onto human cartilage cells in a Petri dish can intensify the breakdown of cartilage tissue. Cholesterol has the same effect in vitro.
In mice, both saturated fatty acids and dietary cholesterol accelerated the progression of injury-related osteoarthritis. But even without injuries, animal fat can cause osteoarthritis-like damage in the knee joints of rats. What about in humans? Osteoarthritis patients generally have higher cholesterol levels in the blood and also in the joints, both in aspirated synovial fluid and in the cartilage itself. Cholesterol exposure worsens the inflammatory degeneration of human cartilage, which could explain why the higher a person’s cholesterol is, the sicker they are.
So could lowering cholesterol with statins help? The data are not clear. Some studies suggest statins help, others found no association, and still others indicate that statins might even lead to worsening. A meta-analysis suggests that the side effects of statins, such as muscle weakness and pain, may outweigh any reduction in osteoarthritis symptoms gained through cholesterol lowering. But you get all the benefits with a healthy plant-based diet, since it lowers cholesterol within a week as much as the starting dose of a statin drug, blood pressure drops, and you lose weight. But does it affect osteoarthritis?
In a study at Michigan State University, men and women with osteoarthritis were randomized to eat a whole-food, plant-based diet or to continue eating as usual. Compared with the control group, the plant-based group showed a significant improvement in physical function and energy/vitality after one week, and pain decreased significantly within two weeks. Of course, many participants also lost substantial weight, but improvements were found even in some who had not lost weight. Since the control group did nothing special, placebo effects cannot be ruled out, but given the many additional benefits, plant-based eating is worth a try.
The researchers suspect that the decline in pain on a plant-based diet is due to lower intake of arachidonic acid, a pro-inflammatory omega-6 fat found primarily in eggs and chickens. NSAIDs such as aspirin reduce pain by blocking the cascade of inflammatory mediators our bodies make from arachidonic acid. By restricting consumption of chicken and eggs, the thinking goes, fewer pain-triggering compounds can form in the first place. (The poultry industry proposed genetically manipulating chickens so they would have less arachidonic acid in their muscles to reduce health risk to humans, but this has not yet been implemented.)
But perhaps it was the anti-inflammatory effect of the plants consumed that was responsible for the rapid pain relief. A pro-inflammatory diet is associated with more severe osteoarthritis pain and also with an increased risk of developing it in the first place. So what do fiber—the most anti-inflammatory dietary component—do? If we eat whole-grain barley in the evening, for example, it is the breakfast the next morning for our good gut bacteria, and we know that the short-chain fatty acid butyrate is then released into the bloodstream, where it has diverse anti-inflammatory effects. In vitro, inflammation-related cartilage loss is significantly reduced when butyrate is dripped onto cartilage pieces from the leg bones of joint-replacement patients.
In the study “The association between fiber intake and the course of knee pain,” almost 5000 men and women were followed for an average of eight years. The researchers observed that the risk of later moderate to severe knee pain was significantly lower among those who consumed at least the recommended fiber intake of about 25 grams per day. In addition, in two cohorts from the famous Framingham Heart Study, which is still ongoing today, higher fiber consumption was found to lower the risk of osteoarthritis symptoms. Mice are protected from osteoarthritis when they eat extra fiber, but there is not yet an intervention study in humans.
Beverages
Free radicals also play a role in joint inflammation and cartilage loss. Observational studies linked higher intake of certain antioxidants with fewer cartilage defects and slower progression of osteoarthritis, but when antioxidant supplements were studied, the results were largely disappointing. (At least they didn’t make things worse, unlike vitamin C in an animal experiment on osteoarthritis.)