Dr Thivi Maruthappu and Professor Christopher Griffiths discuss the expanding role of nutrition in the management of common chronic skin conditions.
Psoriasis is a common chronic inflammatory skin condition that can have an enormous impact on quality of life. Affected individuals develop red, itchy and painful plaques on their skin with overlying scales that can cause both discomfort and shame. Medical management of psoriasis includes topical treatments such as vitamin D and steroid-based creams and ointments, light therapy and immunosuppressive medications such as methotrexate and ciclosporin. Over the last two decades, numerous biologic therapies have also been developed to treat psoriasis.
In recent years it has become apparent that the inflammation of psoriasis is not limited to the skin, but is also associated with the metabolic syndrome (including hypertension, non alcoholic fatty liver disease [NAFLD], insulin resistance, hyperlipidaemia and atherosclerosis). Epidemiological studies have strongly linked psoriasis to cardiovascular disease3 and obesity is a shared characteristic of this cluster of risk factors. Longitudinal population-based studies attribute a causal role for obesity in the development of psoriasis and psoriatic arthritis (PsA) linking it to increased disease severity and a 50% reduction in treatment response.4,5 Furthermore, a meta-analysis has demonstrated that a reduction in body mass index (BMI) of at least 5% in people with obesity and psoriasis resulted in a significant improvement in psoriasis severity.6
Despite this, there is a critical lack of evidence on the relationship between psoriasis and diet, nor is there specific, evidence-based guidance on diet for patients with psoriasis. Rather, recommendations are based on existing guidance for patients with cardiovascular disease. The Medical Board of the National Psoriasis Foundation in the USA strongly recommends dietary weight reduction with a hypocaloric diet in overweight and obese patients with psoriasis but fails to make specific dietary recommendations about which particular diet may be of benefit.7
The Mediterranean diet is one of the most highly studied dietary patterns, and has consistently demonstrated utility in reducing the incidence of major cardiovascular events in high-risk individuals when compared with a low-fat diet.8 The traditional Mediterranean diet is characterised by a high intake of olive oil, fruit, nuts, vegetables and cereals, a moderate intake of fish and poultry and a low intake of dairy, red meat, processed meats and refined sugars.9 Observational studies have identified low levels of adherence to a Mediterranean diet in patients with severe psoriasis; olive oil and fish consumption are independently predictive for PASI (Psoriasis Activity and Severity Index) and C-reactive protein levels.10,11 The authors of these studies attribute the Mediterranean diet’s ability to reduce chronic systemic inflammation to the anti-inflammatory properties of dietary fibres, antioxidants and polyphenols that are rich in this pattern of eating.
Recently there has been growing interest in the role of temporal patterns of energy intake across the day and intermittent energy restriction in the management of a number of chronic inflammatory states such as the metabolic syndrome, arthritis and multiple sclerosis. However, to date, no studies have explored whether restriction of eating time windows could be effective in the management of psoriasis.
The APPLE study will explore this in two ways – firstly a cross-sectional observational study of patients with psoriasis to examine current dietary patterns and compare these with the UK control population. The second aspect of the study will conduct a small clinical trial comparing a Mediterranean-style diet with a time-restricted Mediterranean style diet, assessing several clinical and biochemical parameters to determine response. We hope that this study will help to shed light on the role of nutrition in the management of psoriasis.