Or is it the other way around? Researchers want to know.
Research has found a definite association between being overweight and having psoriasis and psoriatic arthritis, but medical experts continue to study how the two are linked.
The question of which comes first—whether obesity leads to psoriasis or the other way around—is something like the age-old puzzle: Which came first, the chicken or the egg?
"There's no solid answer," says Dr. Kristina Callis Duffin, assistant professor of dermatology at the University of Utah School of Medicine in Salt Lake City. "That's the issue. Nobody knows still."
But physicians are starting to believe that the connection goes both ways. For instance, recent studies showed that having a high body mass index, or BMI, at an early age is associated with the development of psoriasis later in life, says Dr. Abrar A. Qureshi, vice chairman of dermatology at Boston's Brigham and Women's Hospital and an assistant professor at Harvard Medical School. BMI is a measure of one's body-fat content, a way to estimate whether a person is an appropriate weight based on height.
Likewise, "There are studies showing that people (with psoriasis) don't exercise or eat as well, because they don't feel good about their bodies," Duffin points out. Some studies have found that patients gain weight after the onset of psoriasis. Explanations proposed for this relationship include increased social isolation, unhealthful dietary habits, depression and alcohol consumption, as well as decreased physical activity, particularly after developing psoriatic arthritis.
By the same token, there also is strong evidence that obesity predisposes individuals to the development of psoriasis. A large study of female nurses—78,626 total women, 892 of whom self-reported having psoriasis—found that weight gain placed individuals at an increased risk for the subsequent development of psoriasis.
In addition, Qureshi says, researchers have observed that the severity of psoriasis is linked with being more obese; that is, patients with the most severe psoriasis tended to have higher BMIs. Obesity is defined as a BMI of 30 or higher, whereas morbid obesity is a BMI of 35 or more.
Utah researchers looked at the risk of psoriatic arthritis among 943 patients with psoriasis.
Among their findings:
- At the age of 18, 14 percent of the patients were classified as overweight and 5 percent as obese.
- A total of 250 patients went on to develop psoriatic arthritis and analysis showed that the risk of developing the condition was higher among psoriasis patients who were overweight at age 18, and even more so for those who were obese.
Duffin notes that psoriasis patients who were overweight or obese developed psoriatic arthritis earlier than psoriasis patients of a healthy weight.
Inflammation may be the key
Doctors now understand that psoriasis and psoriatic arthritis are inflammatory diseases. Similarly, obesity is associated with inflammation. These connections help explain how obese patients may be predisposed to the development of psoriasis.
Researchers think that as increased body fat is associated with higher levels of inflammatory cytokines known to be involved in psoriasis, this "inflammatory milieu" could increase the risk of psoriatic arthritis. "I always called cytokines ‘the cheerleaders of inflammation,' " Duffin says. "If you have more of these substances, you are more at risk of developing psoriasis."
Obese patients can be harder to treat effectively.
A paper by the National Psoriasis Foundation Medical Board, published in 2010 in the Journal of the American Academy of Dermatology, states that when compared with psoriasis patients who are not overweight, obese patients with psoriasis are more likely to experience certain adverse effects to medications and are less likely to respond favorably to systemic therapies.
Qureshi and Duffin advise dermatologists and rheumatologists to discuss the risks of being overweight with their patients. "Certainly it behooves us to counsel (patients) about diet and exercise," Qureshi says, adding that we now know psoriasis and psoriatic arthritis patients are more prone to related health problems such as high blood pressure, diabetes and cardiovascular disease—all of which are more prevalent in obese people.
"It's important to try to maintain a healthy body weight," Duffin adds. "You want to lose weight, because you want to prevent these other (serious diseases)." Referrals to a dietitian may be appropriate. Weight loss, she says, is "best done under the supervision of a primary care physician."
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