Many of our patients with skin disease inquire about potential dietary changes. In the case of psoriasis and diet, a large body of scientific evidence now supports the role of dietary change as an adjunct to medical therapy. However, misconceptions abound in this area, especially online, and it is therefore critical that physicians serve as a source of evidence-based advice.
In discussing the link between diet and any inflammatory skin condition, one helpful approach is to utilize a framework focusing on three main areas: potential comorbidities, “helpers”, and “triggers”. First, are there any associated comorbidities for which dietary change may be helpful? Second, are there any dietary patterns, foods, or nutrients that may improve skin disease? Finally, are there any dietary patterns, foods, or nutrients that may act to worsen the skin disease?
In the case of psoriasis, there are important considerations in each of these areas.
COMORBIDITIES
The importance of diet must be emphasized to every patient with psoriasis, as a large body of research has demonstrated that patients are at higher risk for multiple comorbid conditions. These comorbid conditions carry serious risk. A recent meta-analysis found that psoriasis is associated with an increased risk for mortality from all causes. In the area of cardiovascular mortality, this risk increases in association with disease severity. (Dhana 2019)
This increased risk of vascular disease has been recognized for decades. (McDonald 1973) A number of large epidemiologic research studies have continued to add to this body of evidence, and together present substantial evidence that patients with psoriasis are at higher risk for diabetes, hypertension, dyslipidemia, and cardiovascular disease. (Takeshita 2017, Mehta 2010)
This represents an important health education target for our patients, as each of these serious systemic conditions are impacted by modifiable risk factors. In other words, behavioral change by an individual patient may strongly influence their risk of serious systemic disease.
The data is compelling. One meta-analysis of 27 observational studies found that psoriasis is associated with both an increased prevalence and incidence of diabetes. (Armstrong 2012) A review of 25 observational studies covering more than 250,000 patients with psoriasis found that psoriasis was significantly associated with greater odds of dyslipidemia. (Ma 2013)
In terms of cardiovascular disease, a diagnosis of psoriasis alone may serve as an independent risk factor for myocardial infarction (MI). In a population-based study involving more than 130,000 psoriasis patients and more than 500,000 controls, patients with psoriasis had an increased adjusted relative risk for MI even after adjustment for hypertension, diabetes, and hyperlipidemia. (Gelfand 2006)
While a number of trials are underway to determine the role of systemic psoriasis therapies in reducing the risk of CVD, (Yang 2016) it is important to emphasize to our patients that risk reduction strategies are available today, even without the use of pharmaceutical medications. Specifically, lifestyle interventions are considered foundational therapy for reducing cardiovascular risk. Dietary intervention is certainly a foundational therapy in the prevention of diabetes, hypertension, and dyslipidemia. Overall, dietary interventions have focused on dietary profiles that may be considered anti-inflammatory. In one randomized trial, a Mediterranean-style diet intervention resulted in reduction in C-reactive protein and IL-18 levels, as well as improvement in endothelial function scores. (Esposito 2004)
Given the increased risk of comorbidities, the National Psoriasis Foundation has recommended screening for CVD risk factors in patients as young as 20 years of age. Despite this recommendation, researchers have found that primary care physicians and cardiologists may not routinely screen psoriasis patients. (Parsi 2012) Therefore, dermatologists play a critical role in educating our patients about comorbidity risk.
Beyond referral to primary care physicians for evaluation, dermatologists may also provide routine screening. Especially with the advent of Medicare incentive programs, many dermatologists routinely record height and weight measurements and perform blood pressure screenings, and may then refer obese or hypertensive patients for further care. Dermatologists may also play an important role in diabetes prevention. Screening may be easily performed via a single non-fasting blood test for serum hemoglobin A1C.
This is particularly important, given the current epidemic of diabetes and prediabetes in the United States. It is estimated that over 33% of US adults had prediabetes in 2015, and nearly half of those older than 65 had prediabetes. (CDC 2019) Alarmingly, only 11.6% of adults with prediabetes reported being informed of this by a health professional.
If a screening hemoglobin A1C test demonstrates prediabetes in an overweight or obese patient, patients may be referred to a certified Diabetes Prevention Program (DPP). As of 2018, these programs are covered for qualified patients under Medicare. A DPP is a structured intervention consisting of group-based sessions over 1 year. (Ratner 2006) Overall, 25 sessions are included, with instruction and support from lifestyle coaches and a focus on incorporating healthier eating and moderate physical activity into daily life, as well as problem-solving and coping skills. Research has demonstrated that this program is effective: in an RCT, there was a reduction of 58% overall in new cases of type 2 diabetes. (NEJM 2002) An additional benefit is that of weight loss, with programs aiming for a 7% weight reduction goal.
HELPERS
Multiple RCTs have demonstrated that dietary interventions may improve both the skin findings of psoriasis (Jensen 2013, Upala 2005, Naldi 2014) as well as the response to systemic treatment. (Gisondi 2008, Esposito 2009) Specifically, lifestyle interventions that resulted in weight loss in overweight or obese psoriasis patients have resulted in improvement of cutaneous findings. In a systematic review, the medical board of the National Psoriasis Foundation reviewed a total of 55 studies to make dietary recommendations for adults with psoriasis. These studies represented over 77,000 participants including over 4500 individuals with psoriasis. Based on this review, they “strongly recommend dietary weight reduction with a hypocaloric diet in overweight and obese patients with psoriasis.” (Ford 2018)
A recent Cochrane systematic review examined the role of lifestyle intervention programs in psoriasis. A total of 10 RCTs, with over 1100 participants, were included. Overall, the authors concluded that caloric restriction resulting in weight loss may lead to significant improvements in PASI scores. (Ko 2019) As the authors of a review on weight loss interventions in psoriasis wrote, weight loss may be considered a useful preventative or adjunctive therapy in psoriasis. (Debbeneh 2014)
Certified Diabetes Prevention Programs, as outlined in the previous section, may be considered one well-researched weight loss intervention, as the programs include a weight loss goal of 7%.
TRIGGERS
Many patients inquire about the role of gluten in psoriasis. This may be due to the fact that several case reports have documented major improvement in psoriasis symptoms with a gluten-free diet (GFD) in patients with both psoriasis, gluten sensitivity and celiac disease. (Addolorato 2003) However, it is important to educate patients on the fact that only some patients may benefit from such an approach.
Psoriasis is associated with a higher risk of celiac disease. Although estimates vary, one large study demonstrated a 2.2-fold higher risk of celiac disease when compared to matched controls. (Wu 2012) In patients with gastrointestinal symptoms or a family history of celiac disease, referral and further evaluation by gastroenterology is warranted.
However, even in the absence of celiac disease, some patients with psoriasis may demonstrate gluten antibodies. In one analysis, approximately 5% of patients without psoriasis demonstrated gluten antibodies, with the number rising to 14% in those with psoriasis. (Bhatia 2014) One small study suggested that patients with gluten antibodies may experience significant cutaneous improvement on a GFD. (Michaëlsson 2000) In this study, 30 patients with psoriasis and gluten antibodies were advised to follow a GFD for three months. At the end, all experienced notable improvement in psoriasis severity scores. Of note, 16 of these 30 patients had normal duodenal histology by biopsy. When a gluten-containing diet was resumed, 18 of the 30 patients worsened.
Importantly, a comparison group of 6 patients who lacked gluten antibodies experienced no improvement on a GFD. This is an important point to emphasize in patients without celiac disease or gluten antibodies.
CONCLUSION
Dietary change should be considered adjunct therapy in the treatment of psoriasis. Patients with psoriasis are at higher risk for multiple comorbid conditions, including diabetes, hypertension, dyslipidemia, and cardiovascular disease. Dietary recommendations are considered a foundational approach in the prevention of all. Dermatologists play an important role in educating our patients on the increased risk for these conditions, and should screen and refer when indicated. Referral to a certified Diabetes Prevention Program should be considered for overweight or obese patients with prediabetes, as these structured programs reduce the risk of progression to diabetes. Importantly, these programs also focus on weight loss.
Weight loss, overall health improvement, is also considered an important adjunct therapy in overweight or obese psoriasis patients, as it has been demonstrated in RCTs to improve PASI scores and improve response to some systemic therapies.
Finally, patients with GI symptoms or a family history of celiac disease should be referred, as psoriasis patients have an increased risk of celiac disease. Even without celiac disease, patients with celiac antibodies (gluten sensitivity) may respond to a gluten-free diet.
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