Weight, obesity, psoriasis and psoriatic arthritis
ARTICLE SUMMARY: Psoriasis, psoriatic arthritis, and excess weight/obesity are often seen together. While scientists will continue to sort out the precise nature of the causes and links, there are very good reasons right now for obese or overweight psoriasis and psoriatic arthritis patients to work on reducing their weight.
There is a growing body of research – and more than a little conjecture – about the relationship between body weight and psoriatic disease. We try to sort it out for you below.
But first a warning: if you are used to getting your medical “facts” from the media, please be aware they tend to claim that research is far more definitive than the research actually is. The scientific evidence that we have to date is more about “likely” and “suspected” than “proven.”
Is being overweight or obese one cause of, or trigger for, psoriasis or psoriatic arthritis?
Suspected but not certain. More researchers are coming to believe that obesity can make someone more susceptible to psoriasis and psoriatic arthritis. And certainly, the evidence is solid that psoriasis patients, on average, have a body mass index (BMI) higher than people who do not have psoriasis. Put differently, there is a higher rate of obesity among psoriasis patients than among the general population. (BMI is a measure of body fat based on height and weight, and you can measure yours easily with this National Institutes of Health BMI calculator.)
As for psoriatic arthritis (“PsA”), a study found that psoriasis patients who recalled having been overweight or obese at age 18 had a higher rate of psoriatic arthritis later in life than patients who reported they were not overweight at age 18:
“[P]atients who report having been obese at age 18 years are 3 times more likely to develop PsA in the course of their psoriasis than patients with normal BMI at age 18 years.” What’s more, the study found that the likelihood of later PsA rose as BMI at age 18 rose.
(One shortcoming of the study is that weight at age 18 was based on participants’ memories – an average of 30 years after the fact – rather than medical records.)
The fact that two conditions often appear together – psoriasis and obesity – does not prove that one causes the other. Some people theorize that certain hormones found in higher levels in obese people could contribute to psoriasis susceptibility. Or perhaps there are common genes that predispose certain people both to obesity and psoriasis. Certainly, both conditions involve chronic inflammation. Further research will help us learn the answer.
Does psoriasis or psoriatic arthritis contribute to making one overweight or obese?
Some researchers believe that psoriasis and/or psoriatic arthritis contribute to obesity. One theory is that the chronic inflammation of psoriatic disease triggers weight gain in some way. Another theory is that the physical pain (and/or emotional pain and embarrassment) of psoriasis might lead people to exercise less. In addition, the higher rate of depression in psoriasis patients than in those without psoriasis, and even higher depression rate among those with psoriatic arthritis, might also contribute to reduced exercise or consuming more calories as a form of “self-therapy.” But the actual research on this is less definitive than the anecdotal theories.
What if psoriatic disease and obesity both reinforce the other?
Some experts believe both that psoriatic disease makes one more susceptible to obesity, and that obesity makes one more susceptible to psoriasis. In that model, each reinforces the other. The question then becomes whether successful treatment of one can improve the other.
Does being overweight or obese make psoriasis worse? Does losing weight make psoriasis or psoriatic arthritis improve?
Psoriasis patients with a higher BMI tend to have more severe psoriasis, on average, than psoriasis patients with lesser BMI. But to add complexity to the issue, several studies have found that treatment of moderate to severe psoriasis with anti-TNF biologics may lead to weight gain.
In addition, people with severe psoriasis have a higher rate of psoriatic arthritis than patients with mild psoriasis. The reasons for these associations are not yet clear.
A study published in 2013 received widespread media attention with headlines like this one from the NY Times website: “Weight Loss May Ease Psoriasis.” But the actual study – as opposed to the media coverage – did not really deliver that result.
In fact, the study actually found that the 30 participants with psoriasis who did a 16-week intensive weight loss program did NOT have a statistically significant lessening of a key psoriasis severity measurement (called PASI score) as compared to a group of 30 psoriasis patients who did not do the weight loss program.
More promising was a 2014 study that did find a statistically significant improvement in PASI score after 20 weeks for moderate to severe psoriasis patients also on systemic therapies. Those who followed a specific diet and exercise regimen provided them lost more weight and had more improvement in PASI scores than a control group of psoriasis patients who received only a single, 15-minute meeting explaining the benefits of weight loss for psoriasis control – those patients lost less weight and had less improvement in PASI scores.
This could mean that losing weight while on a systemic treatment might boost the systemic medication’s effectiveness on psoriasis, rather than an improvement in psoriasis directly related to the weight loss. (Note that those with psoriatic arthritis were excluded from this study.)
Recall also the research that has shown that anti-TNF biologics may be associated with some weight gain. How complex this puzzle quickly becomes!
Also, the absolute patient numbers driving the findings in the 2014 study are pretty small. For example, 37 of 151 patients in the diet and exercise group achieved 75% improvement in their psoriasis symptoms at week 20, versus 29 of 152 patients in the group that simply received a briefing. That was found to be statistically significant but clearly is not dramatic.
What is still needed is a large study that follows groups of patients for a longer period of time, to see if these findings hold up and can be sustained.
As for psoriatic arthritis, there is evidence, largely done in research on other types of arthritis, that a reduction in BMI can reduce the negative effects of arthritis.
Despite some still-unresolved questions, our patient-to-patient recommendation, based on everything we have studied by scientists and physicians working in this area, is that there are very good reasons right now for obese or overweight psoriasis and psoriatic arthritis patients to work on reducing their weight/BMI, even if the studies to date are not airtight.
Increasingly powerful evidence is piling up that psoriasis is associated with heart disease, heart attack, stroke, diabetes and other diseases, many of which are also linked to obesity. This makes it more important than ever for psoriasis patients – who can’t yet cure their psoriasis – to address other risk factors for these other diseases that can be addressed, like smoking and excess weight. (Please read more on these issues here.)
So while weight reduction is difficult to achieve, and even harder to maintain over time, it is worth the sustained effort.
From diabetes and heart disease to, very possibly, psoriasis, losing excess weight can improve your quality of life and possibly extend it.