Psoriasis has been associated with a number of serious co-morbidities, including obesity. The mere association between psoriasis and obesity implies an increased prevalence of major cardiovascular risk factors, including diabetes, hypertension, hyperlipidemia, and smoking, in addition to obesity among psoriasis patients. Obesity, hyperlipidemia, hypertension, and insulin resistance constitute what is known collectively as the metabolic syndrome. General risk factors associated with metabolic syndrome include a diet high in saturated and trans fats, a sedentary lifestyle, cigarette smoking, alcohol consumption, and stress. The diagnosis of metabolic syndrome carries with it an increased risk of cardiovascular morbidity and mortality.
The association between psoriasis and metabolic syndrome carries important public health implications and has prompted a growing body of research. The intent of the current pilot study is to evaluate modifiable metabolic syndrome- associated risk factors, including obesity, stress level, physical activity, and dietary habits, among psoriasis patients as compared to control patients.
A convenience sample of patients with plaque psoriasis presenting to the UCLA General Medical Dermatology Clinic from August 8, 2006 to August 8, 2008 were invited to enroll in the study. All non-psoriasis patients visiting the UCLA General Medical Dermatology Clinic were invited to serve as controls and underwent the same procedures except for PASI calculations. All subjects who enrolled in the study were provided with detailed information regarding the objectives and were asked to sign an informed consent form prior to participation. Baseline medical history and demographic data were collected from all patients. Information regarding smoking history and alcohol use was acquired. Patients were asked to indicate whether they currently smoke cigarettes, did so in the past, or never before. They also categorized the frequency of their drinking habits as, “Don't drink; Recreationally/socially; A few drinks/week; A few drinks/day.”
Body mass index (BMI) was calculated based on height and weight. Obesity was defined as a BMI ≥30 kg/m2. A series of questionnaires were administered including the Perceived Stress Scale (PSS), the Godin Leisure-Time Exercise Questionnaire (GLTEQ), and the Rapid Eating Assessment for Patients (REAP). For plaque psoriasis subjects, PASI scores were assessed by the study physician (MWC).
The PSS was designed to measure the degree to which situations in one's life are appraised as stressful. The 14 items in the scale ask about feelings and thoughts regarding specific circumstances during the last month. The alpha reliability coefficient for PSS14 was 0.75. The GLTEQ scores the frequency of strenuous (e.g., running), moderate (e.g., fast walking), and mild (e.g., easy walking) exercise for more than 15 minutes in a typical week. The two-week test–retest reliability of the measures of total leisure activity and the frequency of activity that works up a sweat have been estimated to be 0.74 and 0.80, respectively. High scores on both questions reflect high levels of physical activity. The REAP questionnaire is a brief validated instrument that serves as a concise assessment of an individual's diet and physical activity. The survey includes 27 questions assessing intake of fruits and vegetables, total and saturated fats, cholesterol, sweets, and sodium with higher values indicating better nutrition.
Previous studies have shown an association between psoriasis and metabolic syndrome; however, the nature of this relationship is unclear. Poor dietary and exercise habits are considered to be modifiable lifestyle risk factors contributing to metabolic syndrome. It appears from the sample that on average, psoriasis patients may have poorer dietary habits and a trend toward reduced physical activity compared to controls.
Psoriasis patients in our study had a higher average BMI than their control counterparts. Therefore, our study suggests that poor dietary and exercise habits may be factors contributing to obesity and metabolic syndrome in psoriasis patients. In addition, smokers and heavier patients were found to have more severe and extensive psoriatic skin involvement. Among psoriasis subjects, there was a trend, although not statistically significant, for heightened stress to also be associated with increased severity of skin disease.
Similar to previous studies, we found an increased prevalence of obesity among psoriasis patients (30 percent) compared to controls (18 percent), which is in line with the results of the Utah Psoriasis Initiative. Furthermore, in contrast to previous studies, we did not find an increased prevalence of metabolic syndrome-associated diseases among psoriasis patients compared to controls. Subject self-reporting, the high frequency of under diagnosis of these conditions among psoriasis patients, as well as our small sample size are likely responsible for the discrepancy between our results and that of previous studies.
The diagnosis of psoriasis and the profound adverse effects on patients' well-being may trigger stress responses including overeating, inactivity, and smoking. Although we did not find increased alcohol consumption among psoriasis subjects in our study, we did find that psoriasis subjects were more likely to be current smokers. The nutrition results of our study demonstrate a larger proportion of psoriasis patients with poor nutrition habits in terms of REAP score, and a trend toward increased total fat, saturated fat, and cholesterol compared to controls. In our study, although there was a trend for psoriasis subjects to exercise less than controls, this difference was not statistically significant. Poor nutrition and reduced physical activity may represent modifiable lifestyle choices contributing to metabolic syndrome in psoriasis patients.
Among psoriasis subjects, we were interested in identifying potential factors contributing to an increased severity and extent of disease as measured by PASI. For example, our study confirmed previous findings from the literature showing a positive correlation between BMI and psoriasis severity. We did not, however, find a correlation between exercise or poor dietary habits and the severity of skin disease as had been proposed in previous studies. We did find current smokers, subjects using systemic treatment, as well as those reporting increased stress tended to have higher PASI scores than their non-psoriasis counterparts, which is in agreement with findings in the literature.
Aside from the limitations of our study mentioned previously, there are some additional limitations to acknowledge. In particular, our small sample size and the use of a convenience sample among patients presenting to our specialty clinic limits the generalizability of our conclusions. Due to the pilot nature of this study, a sample size calculation was not performed, thus it is possible that our study had too small of a sample size to detect small differences between the psoriasis and control groups. In addition, PASI measurements were limited to plaque psoriasis patients only, thus excluding subjects with erythrodermic, guttate, and pustular forms of psoriasis. Since all the subjects were collected in just one center, there may also be a sample bias. Subjects may have felt compelled to answer questions in the survey in a certain way leading to response bias. Since subjects were asked to recall aspects of their daily lifestyle and medical history, there may be some component of recall bias.
Psoriasis is associated with an increased risk of morbidity and mortality, a higher prevalence of metabolic syndrome, and a higher frequency of cigarette smoking. Furthermore, obese patients may have increased severity of psoriatic disease. Our study suggests that poor dietary and perhaps exercise habits may contribute to obesity and metabolic syndrome in psoriasis patients. It is important for physicians to be aware of these associations and to reduce these risks in psoriatic individuals in order to lessen comorbidity and mortality. Future research can build upon this pilot study by taking a prospective longitudinal approach and applying a more rigorous evaluation of lifestyle factors that may be associated with the increased prevalence of metabolic syndrome in a larger sample of the psoriatic population.
Adapted from a presentation given at the Cosmetic Surgery Forum 2011 in Las Vegas, NV (cosmeticsurgeryforum.com). This presentation was selected as one of the top 10 resident presentations at the meeting.
Jennifer Ahdout is a second-year dermatology resident at UC Irvine. She recently started a dermatology free clinic to reach out to the uninsured and indigent population of Orange County. She is also active in the legislative arena in her role as the AAD's resident representative to the American Medical Association (AMA) as well as a delegate to the AMA's resident and fellows section.