How Fat Affects Arthritis
Being overweight can make arthritis, gout, lupus, fibromyalgia and other joint diseases and conditions worse.
If you were to ask people to name a health problem related to obesity, odds are good they’d say “heart disease” or “diabetes.” And they’d be right; those two chronic diseases have a very strong relationship to excess weight. They are the safe bets.
But if you like long odds, put your money on arthritis. It’s not as commonly known, but obesity in some cases raises the risk of getting a certain type of arthritis; in all cases, obesity makes arthritis worse. One in 5 Americans has been diagnosed with arthritis, but according to the Centers for Disease Control and Prevention (CDC), that number jumps to more than 1 in 3 among obese people – and 2 out of 3 Americans are either overweight or obese.
Here’s a look at what fat does to arthritis, as well as some tips to put you on the road to losing weight.
Fat and Osteoarthritis
Osteoarthritis, OA, is the most common type of arthritis, affecting approximately 27 million Americans. It is characterized by the breakdown of cartilage – the flexible but tough connective tissue that covers the ends of bones at joints. Age, injury, heredity and lifestyle factors all affect the risk of OA.
Why Obesity Matters
OA has a logical link to obesity: The more weight that’s on a joint, the more stressed the joint becomes, and the more likely it will wear down and be damaged.
“Weight plays an important role in joint stress, so when people are very overweight, it puts stress on their joints, especially their weight-bearing joints, like the knees and the hips,” says Eric Matteson, MD, chair of the rheumatology division at the Mayo Clinic in Rochester, Minn.
Every pound of excess weight exerts about 4 pounds of extra pressure on the knees. So a person who is 10 pounds overweight has 40 pounds of extra pressure on his knees; if a person is 100 pounds overweight, that is 400 pounds of extra pressure on his knees. “So if you think about all the steps you take in a day, you can see why it would lead to premature damage in weight-bearing joints,” says Dr. Matteson.
That’s why people who are overweight are at greater risk of developing arthritis in the first place. And once a person has arthritis, “the additional weight causes even more problems on already damaged joints,” says Dr. Matteson.
But it’s not just the extra weight on joints that’s causing damage. The fat itself is active tissue that creates and releases chemicals, many of which promote inflammation.
“These chemicals can influence the development of OA,” explains Jeffrey N. Katz, MD, a professor of medicine and orthopaedic surgery at Harvard Medical School and Brigham and Women’s Hospital in Boston.
This effect can be seen in the numerous studies that have linked extra weight to hand OA. “Obviously, you don’t walk on your hands, so there may be something that is produced by fat cells in the body that causes the joint to break down more rapidly than it might otherwise,” says David Felson, MD, a professor of medicine and epidemiology at Boston University School of Medicine.
For both reasons – excess joint stress and inflammatory chemicals – fat should be kept in check among all people, especially those who already have OA.
Fat and Rheumatoid Arthritis
Rheumatoid arthritis, RA, affecting 1.5 million Americans, is an autoimmune disease in which the body’s immune system attacks its own joint tissue. This creates inflammation throughout the body, and can lead to joint erosion and pain.
Why Obesity Matters
The inflammatory chemicals from fat that may play a role in OA are also culprits in RA. Some of these chemicals, called cytokines, can impact different body systems, including musculoskeletal and cardiovascular systems. Many types of cytokines are released by fat tissue, and researchers are working to identify them and understand the specific effects of each kind.
One important group is called adipokines, and most types of adipokines promote inflammation – “not a good thing in RA,” says Jon Giles, MD, an assistant professor of medicine in the division of rheumatology at Columbia University College of Physicians and Surgeons, in New York City.
Other cytokines released by fat include tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1). Both are overactive in RA and cause inflammation. You may be familiar with the biologic drugs that suppress them, including etanercept, brand name Enbrel, and infliximab, brand name Remicade, which target TNF-alpha, and anakinra, brand name Kineret, which targets IL-1.
One type of adipokine, called adiponectin, is good for the heart, because it has an anti-inflammatory effect on blood vessels – but it causes inflammation in joints. When people gain weight, they make less adiponectin, which may be one reason overweight RA patients can have less joint damage than those who are not overweight. But don’t think that means being overweight has a protective effect, says Dr. Matteson of the Mayo Clinic. “In fact, you are still at risk for your arthritis to advance more rapidly in your weight-bearing joints simply because of the biomechanical forces that come into play.”
And people with RA – including those who have a body mass index (BMI) in the normal range – have yet another reason to watch their diet and exercise. “The disease process changes body composition in an unfavorable way; it favors having more fat and less muscle,” says Dr. Giles, who has conducted many studies on the effects of body composition and inflammatory arthritis.
In addition, researchers have found the excess fat is often located around the abdomen (known as visceral fat), which is a risk factor for heart disease and insulin resistance.
“RA patients have a 50 percent higher cardiovascular mortality risk than the general population, so controlling cardiovascular risk factors is a priority in RA patients. You don’t want to have fat that increases your risk of heart disease,” says Dr. Giles.
Fat and Gout
Gout is a form of inflammatory arthritis that occurs when an excess of uric acid in the body leads to the formation of uric acid crystals in the joints, triggering painful attacks. These are most common in the big toe, but also occur elsewhere.
Why Obesity Matters
Obesity is closely linked to gout; as the country’s obesity rate has gone up, so has its rate of gout. According to studies, about 70 percent of people with gout are overweight and 14 percent are obese. Being obese puts a person at a higher risk of developing gout in the first place – and of getting gout 11 years earlier on average than someone of normal weight.
“In the highest [weight] group versus the lowest group, it could be a tenfold or higher risk of developing gout,” says gout expert Hyon Choi, MD, a professor of medicine at Boston University School of Medicine. Dr. Choi has authored pivotal population-based studies examining the link between gout and obesity.
So what is going on? Uric acid is formed when the body breaks down purines – a compound found in human tissue and in most foods, and concentrated in certain meats, seafood and beer. Some people’s bodies produce too much uric acid; other people’s kidneys can’t eliminate it quickly enough.
It’s worse for obese people. “When people are obese, their kidneys can’t excrete efficiently. The prime suspect is insulin,” Dr. Choi says. “When people are big, [their insulin] doesn’t work as well, so they produce more. Insulin inhibits uric acid excretion in the kidneys.”
The good news is that small changes can make a big difference. “Lifestyle matters a lot in gout, like it does for diabetes, so you can control gout if you really stick to good lifestyle [choices]. You can prevent it to large degree. You have a lot more control than in RA,” he says.
Studies have shown that losing even a small amount of weight can lower uric acid levels, and losing more weight has a bigger effect on reducing uric acid. “Losing weight drags down uric acid levels. If you get rid of the root cause, your risk will drop,” says Dr. Choi.
Fat and Psoriatic Arthritis
Psoriatic arthritis (PsA) is a type of inflammatory arthritis that affects up to 30 percent of people with psoriasis, an autoimmune condition that causes scaly and inflamed skin. Psoriasis usually precedes psoriatic arthritis.
Why Obesity Matters
According to studies, obesity is a risk factor for psoriasis and is associated with more severe disease. People with psoriasis are more likely than people without it to have a higher BMI and higher levels of the obesity-related hormone leptin. One of the first studies to look at the link between psoriasis and the development of PsA found that psoriasis patients who are obese at age 18 had triple the risk of developing PsA than those with a normal BMI – and they developed PsA earlier in life.
“It is a double whammy; first they get psoriasis, then they get psoriatic arthritis,” says Dafna Gladman, MD, professor of medicine at the University of Toronto and co-author of many studies on psoriatic arthritis.
The exact mechanism, however, is unknown. “There are a lot of metabolic things going on [in obesity] – adiponectin, leptin, pro-inflammatory cytokines that are increased. We don’t know if it is just the fat, or if it is what the fat is associated with,” says Dr. Gladman.
What is certain is that being overweight or obese plays a role in PsA. “Because you carry around more weight, especially in the lower extremities and back, there are additional forces at play,” says Dr. Gladman. “Also, when you are overweight, it’s difficult to figure out the dose of medication you might need. [Dosing of] Remicade is weight-related, but other drugs don’t have that, so obese patients may be undertreated because we don’t know the precise dose we should be using.”
Fat and Lupus
Systemic lupus erythematosus is a chronic, inflammatory autoimmune disease in which the body’s immune system mistakenly attacks its own tissues and organs.
Why Obesity Matters
Several studies have found that the rates of obesity are higher in people with lupus than in the general population. Obesity in patients with lupus is associated with high levels of disability and possibly cognitive impairment.
“What we found is that there is a higher rate of obesity among women with lupus than there is in general population, and there is a big effect of obesity on functioning,” says Patricia Katz, PhD, professor of medicine and health policy at the University of California, San Francisco.
In one of her numerous lupus studies, obese lupus patients performed significantly worse than those who were not obese in three areas of functioning: work, basic physical functions (such as climbing stairs or bending over) and daily activities (including self care and social activities).
“Not only did obese women do worse at first look, but they had greater decline in functioning,” says Katz.
In another study, obese and/or inactive women with lupus had a higher rate of cognitive impairment – although it didn’t show that one condition caused the other.
As in OA and RA, the cytokines that fat releases create inflammation in different parts of the body. “Fat tissue is not inert,” Katz says, echoing other researchers.
But it’s hard to know if obesity is a cause or an effect of health risks associated with lupus, she says. For example, people with lupus have a higher risk of heart disease. “If you are fat, maybe you release more inflammatory cytokines, which affects cardiovascular risk.”
In addition, even though obesity is categorized as a BMI of 30 or more, Katz’s studies have found that patients with lupus who have a BMI of 27 have the same cardiovascular risk factors and disability as heavier lupus patients. “Really, if you want to set a criterion for obesity in lupus using BMI, you need to move the number lower, to 26.8,” she explains.
And, as with other forms of arthritis, there’s the issue of body mechanics. “If you are obese, the loading on your joints will make the pain worse,” she says.
Fibromyalgia is a chronic pain disorder that affects 3 to 6 percent of Americans, mostly women. Symptoms are widespread muscle pain and “tender points,” and can include fatigue, sleep problems, depression, bladder and bowel irritability and cognitive difficulties.
Why Obesity Matters
Eighty percent of people with fibromyalgia are overweight or obese, compared with 67 percent in the general population. Numerous studies have shown that heavier fibromyalgia patients have worse symptoms and a lower quality of life than those of normal weight. Additionally, being overweight, especially if you are inactive, puts you at greater risk of developing fibromyalgia, according to a large Norwegian study.
Both fibromyalgia and obesity are characterized by the malfunctioning of the HPA axis – a communication system between glands that helps regulate the immune system, digestion, mood, hormones and other functions.
Understanding the HPA axis issue could lead to better treatments for both conditions, says Akiko Okifuji, PhD, a psychologist at the Pain Research and Management Center and professor at the University of Utah, in Salt Lake City.
Each condition poses “a potential barrier to treat the other,” says Okifuji. “In order to help people attain reduction in symptoms and weight, we have to target both.”