Psoriasis is a chronic inflammatory disease of the skin and joints (psoriatic arthritis in 20–30% of cases) with a strong immune-mediated component (overproduction of Th1 and Th17 T cells and inflammatory cytokines such as IL-17, IL-23, and TNF-alpha). It affects 2–3% of the Italian population (approximately 1.5–2 million people). Psoriatic plaques (areas of reddened, thickened skin with white-silvery scales) are the most visible symptom, but the disease is systemic: patients with moderate-to-severe psoriasis have an increased risk of metabolic syndrome, type 2 diabetes, cardiovascular disease, inflammatory bowel disease, and depression. The chronic systemic inflammation that characterizes psoriasis is modulated by both genetics and environment, including diet. This opens concrete space for nutritional interventions that reduce overall inflammatory burden and improve response to pharmacological therapy.

Modifiable risk factors: obesity, alcohol, smoking

Risk factors that significantly worsen psoriasis and can be modified through lifestyle changes. Obesity: the obesity-psoriasis relationship is bidirectional and very robust. Elevated BMI is associated with: greater severity of psoriasis (PASI score positively correlated with BMI), reduced response to biologic drugs (monoclonal antibodies are dosed in mg/kg: overweight = higher absolute dose but often the dose-response relationship is not linear), increased risk of psoriatic arthritis. Cohort studies show that every 5 kg reduction in body weight reduces PASI score by 1–2 points. A 5–10% weight reduction in overweight patients significantly improves psoriasis severity even without changing pharmacological therapy. Alcohol: alcohol is a well-documented trigger for psoriasis flares. Mechanisms: alcohol increases TNF-alpha and IL-6 levels (cytokines central to psoriasis), inhibits keratinocyte apoptosis response, reduces drug efficacy. Alcohol reduction improves therapy response in observational studies. Complete abstinence is recommended in moderate-to-severe forms. Smoking: cigarette smoking increases psoriasis risk (RR 1.7 for smokers) and psoriatic arthritis risk (RR 2.1). Smoking cessation improves disease course. The smoking-psoriasis association is strong and biologically plausible (smoking increases systemic oxidative and inflammatory burden).

The Mediterranean diet in psoriasis: the evidence

The Mediterranean diet shows the strongest evidence among dietary patterns for psoriasis management. A study by Barrea et al. (Nutrients, 2015, 62 patients): adherence to the Mediterranean diet (measured by Mediterranean Diet Score, MDS) is inversely correlated with psoriasis severity (PASI). Patients with greater Mediterranean diet adherence have a PASI score on average 3–4 points lower than those with less adherence: a clinically significant difference. Proposed mechanisms: reduction of systemic inflammation (the Mediterranean diet reduces CRP, IL-6, TNF-alpha: all cytokines relevant to psoriasis), favorable effect on the microbiome (intestinal dysbiosis is documented in psoriasis: the psoriasis microbiome is characteristically altered), reduction in body weight (the Mediterranean diet promotes maintenance of normal weight), omega-3 intake (fatty fish, walnuts: direct anti-inflammatory effect). Intervention studies with Mediterranean diet in psoriasis: a small RCT (Lima et al., 2020, 30 patients) shows 28% reduction in PASI score after 12 weeks of Mediterranean diet vs normal diet. It's not a large study, but the direction is consistent with observational data.

Omega-3 and other nutrients in psoriasis

Omega-3 (EPA and DHA): a meta-analysis by Millsop et al. (JAAD, 2014, on 6 RCTs) shows that omega-3 supplementation (1.8–10 g/day of EPA+DHA) reduces itching, scaling, and psoriatic erythema in a statistically significant manner vs placebo. The effect is modest but consistent. The mechanism: omega-3s compete with arachidonic acid (omega-6, precursor of pro-inflammatory prostaglandins), reducing production of LTB4 and PGE2 (mediators of psoriasis inflammation). Recommended supplementation: 2–4 g/day of EPA+DHA (fish oil or krill oil) for at least 12 weeks. Fatty fish (salmon, sardines, mackerel, herring: 2–3 servings per week) is preferable to supplements when possible. Vitamin D: nearly all psoriasis patients have insufficient vitamin D levels. Vitamin D has a direct role in regulating keratinocyte proliferation (skin cells that multiply excessively in psoriasis) and in modulating immunity. Topical vitamin D (calcipotriol, ointments) is one of the standard dermatological treatments for psoriasis. Systemic vitamin D (oral supplementation) has more modest but documented effects. Target: 25-OH vitamin D above 40 ng/mL. Zinc: some small studies show psoriasis improvement with zinc supplementation. Data not definitive but plausible: zinc has anti-inflammatory and immune-modulating properties. Recommended dose if deficiency is documented: 30–45 mg/day of elemental zinc. Do not supplement without documenting deficiency: excess zinc causes toxicity.

Gluten-free diet and psoriasis: when it makes sense

Many psoriasis patients report online improvements with a gluten-free diet. The scientific reality is more nuanced. The psoriasis-celiac connection: there is a statistical association between psoriasis and celiac disease (and non-celiac gluten sensitivity, NCGS). Psoriasis patients have a celiac prevalence of 3–4% (vs 1% in the general population) and positive anti-gliadin IgA/IgG antibodies of 10–14%. A gluten-free diet in psoriasis makes sense only if: celiac disease is documented (positive serology + biopsy): in this case GFD is mandatory regardless of psoriasis, and several studies show PASI score improvement with GFD in celiac psoriasis. Anti-gliadin IgA or IgG antibodies are positive (suspected NCGS): in this case a study by Addolorato et al. (JAAD, 2003) shows PASI score reduction with GFD. Without documented celiac disease and without positive antibodies: there is no evidence of GFD benefit on psoriasis. GFD without indication is difficult, costly, and risks creating nutritional deficiencies. Before starting GFD for psoriasis: ask your specialist for celiac screening (anti-tTG IgA, total IgA, anti-gliadin) while still on a gluten-containing diet.

The microbiome and psoriasis: connections and strategies

Psoriasis is characterized by alterations in both skin and intestinal microbiota. The skin microbiome in psoriasis: psoriatic plaques have a different bacterial composition from healthy skin: reduction of Staphylococcus epidermidis (protective) and increase of Staphylococcus aureus and Streptococcus (pro-inflammatory). Some experimental studies suggest that restoring skin microbiome diversity (with topical probiotics: still experimental) could improve psoriasis. The intestinal microbiome in psoriasis: "leaky gut" (increased intestinal permeability) is documented in psoriasis and may contribute to systemic inflammatory burden by allowing bacterial fragments (LPS: lipopolysaccharides) to pass from the intestinal lumen into systemic circulation. Dietary strategies for the microbiome in psoriasis: reduce ultra-processed foods (which increase intestinal permeability through emulsifiers E471, E472, polysorbate 80, lecithin), increase prebiotic fiber (inulin, FOS: nourish beneficial colon bacteria), fermented foods (kefir, organic yogurt, kimchi, miso: increase intestinal bacterial diversity). Probiotics: pilot studies with Lactobacillus rhamnosus, Bifidobacterium longum show EASI score reduction in atopic dermatitis (relative of psoriasis). Not yet conclusive studies on psoriasis specifically.

Psoriasis and metabolic syndrome: integrated management

Psoriasis is closely associated with metabolic syndrome (abdominal obesity + hypertension + dyslipidemia + hyperglycemia): psoriasis patients have a metabolic syndrome prevalence of 30–40% vs 20–25% in the general population. The biological connection: adipose tissue is a source of pro-inflammatory cytokines (adipokines: leptin, resistin, adipocyte TNF-alpha) that fuel psoriasis inflammation. Psoriasis itself promotes insulin resistance through circulating cytokines. Integrated management of psoriasis + metabolic syndrome with diet: hypocaloric diet for weight reduction (benefits on psoriasis are documented), reduction of simple sugars and refined carbohydrates (for insulin resistance), sodium reduction (for hypertension), reduction of saturated fats (for dyslipidemia), increase in omega-3s and fiber. This dietary profile essentially corresponds to a hypocaloric Mediterranean diet: the most suitable approach for integrated management of psoriasis + metabolic comorbidities.