Diet and Psoriasis: Experimental Data and Clinical Evidence

M. Wolters

Disclosures

The British Journal of Dermatology. 2005;153(4):706-714. 

In This Article

Oxidative Stress and Antioxidants

Oxidative stress and increased free radical generation have been linked to skin inflammation in psoriasis. Superoxide anion liberation was elevated in psoriatic dermal fibroblasts, which have been suggested to play a central role in the inflammatory mechanism of psoriasis.[16] Patients with psoriasis exhibit several markers of oxidative stress and show impaired antioxidant status: increased concentrations of malondialdehyde (MDA), a marker of lipid peroxidation, were measured in plasma and red blood cells, and decreased plasma levels of β-carotene and α-tocopherol as well as decreased serum concentrations of selenium were found.[16,47,61] Results on the activity of antioxidant enzymes are inconsistent. In one study glutathione peroxidase activity was stimulated in both erythrocytes and platelets when compared with normal cells. At the same time the plasma selenium concentration was significantly reduced compared with the control group.[27] In another trial, activities of antioxidant enzymes such as catalase and glutathione peroxidase were reduced.[16] An increased production of MDA was consistently observed in psoriasis indicating advanced phospholipid peroxidation of the red blood cell membrane caused by a decrease of antioxidant resistance. This may explain the decreased membrane fluidity associated with the exacerbation of the disease.[16] Fish oil supplementation not only altered the lipid pattern of erythrocyte membranes but also led to a reduction of MDA in patients with psoriasis and therefore may reduce oxidative stress.[27] In an Italian case-control study with 316 patients with psoriasis and 366 controls, dietary intake was assessed by a semiquantitative food frequency questionnaire and data were adjusted for age, sex and BMI. Psoriasis risk (odds ratio) was significantly inversely related to the intake of carrots, tomatoes and fresh fruit as well as to the β-carotene intake. The intake of green vegetables showed an inverse association, with borderline statistical significance. The consumption of vegetables and fruits may be beneficial in psoriasis due to their high content of various antioxidants such as carotenoids, flavonoids and vitamin C.[19]

A sufficient status of antioxidants (e.g. vitamin C, vitamin E, β-carotene and selenium) may be helpful to prevent an imbalance of oxidative stress and antioxidant defence in psoriasis. While ascorbic acid acts as a water-soluble antioxidant,[62]α-tocopherol is a chain-breaking antioxidant that prevents the propagation of lipid peroxidation.[63]β-Carotene displays antioxidant activity by scavenging free radicals and is a potent quencher of singlet oxygen.[64] Selenium is essential for the function of a number of selenoproteins such as glutathione peroxidases and thioredoxin reductase which take part in the antioxidant defence.[65] To date, only a few studies have investigated the effect of antioxidant supplementation on psoriasis symptoms. In one supplementation trial, seven patients with psoriasis received selenium 400 µg daily for 6 weeks as selenomethionine-enriched yeast.[66] Blood and serum selenium levels were normal at baseline. After supplementation there was a slight but significant increase only in the number of CD4+ T cells in the reticular dermis of the psoriatic lesions. Selenium supplementation had no marked effect on the clinical condition of the patients.[66] A previous study also showed no effect of daily supplementation of 600 µg selenium-enriched yeast alone or together with 600 IU of vitamin E on the clinical symptoms of 69 patients with psoriasis. In this placebo-controlled study, blood, plasma and platelet selenium concentrations as well as platelet glutathione peroxidase activity and plasma vitamin E markedly increased in the supplemented group. However, the mean skin selenium concentration and red cell glutathione peroxidase activity remained unchanged.[67]

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