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In this prospective study of US women, we found the risk for psoriasis varied by the amount and type of alcoholic beverage. Although, overall, women who drank more than 2.3 alcoholic beverages per week were at greater risk for psoriasis, nonlight beer was the only alcoholic beverage that increased the risk for psoriasis. The risk for psoriasis was 1.8 times higher among women who consumed 5 or more nonlight beers per week compared with those who abstained from alcohol. When we used a more precise definition for psoriasis, the risk was 2.3 times higher among women who consumed 5 or more nonlight beers per week. These associations were independent of other potential risk factors for psoriasis such as age, smoking, BMI, physical activity, and DFE. The excess risk of psoriasis associated with consumption of at least 5 nonlight beers per week for all NHS II participants was 1.53%; however, this excess risk would likely be more pronounced in the general population where the prevalence of nonlight beer consumption is higher than the prevalence of beer consumption in this cohort. For example, this excess risk increases to 15.3% given the prevalence of drinking in the general US population.20

Nonlight beer was the only alcoholic beverage that increased the risk for psoriasis, suggesting that certain nonalcoholic components of beer, which are not found in wine or liquor, may play an important role in new-onset psoriasis. One of these components may be the starch source used in making beer. Beer is one of the few nondistilled alcoholic beverages that use a starch source for fermentation, which is commonly barley. This differs from wine that uses a fruit source (grapes) for fermentation. Some types of liquors such as vodka may use a starch source for fermentation; however, these starches are physically separated from the liquor during distillation. Starch sources such as barley contain gluten, which has been shown to be associated with psoriasis. For example, individuals with psoriasis have elevated levels of antigliadin antibodies and may have a so called "latent-gluten sensitivity" compared with individuals without psoriasis.21 Several studies have shown that a gluten-free diet may improve psoriasis severity in patients with gluten sensitivity.21-24 One case report describes a patient with celiac disease and psoriasis whose skin lesions improved shortly after starting a gluten-free diet.25 Light beer also contains gluten; however, this study did not show an association between light beer intake and incident psoriasis. This may be owing to the lower amounts of grain used to make light beer compared with nonlight beer (written communication, William Kerr, PhD, July 28, 2009). Although a gluten-free diet helps clear psoriasis,23, 25 it remains unknown whether gluten contributes to new-onset psoriasis and whether this only occurs in predisposed individuals, such as those with latent gluten sensitivity.

Limitations of our study deserve comment. The retrospective recall of psoriasis onset may have led to misclassification of psoriasis onset. We were also unable to examine whether the risk for psoriasis was different for early-onset psoriasis vs later-onset psoriasis given the age of the NHS II cohort at baseline (age, 25-42 years). This well-educated female cohort provides high-quality data with little loss to follow-up but does not represent a random sample of US women. Although the absolute rates of psoriasis and distribution of alcohol intake may not be representative of a random sample of US women, the biological effects of alcohol intake on psoriasis should be similar. Our study was observational; thus, we cannot rule out the possibility that statistical error and unmeasured factors, such as socioeconomic status and stress, might contribute to the observed associations. However, we included as many known risk factors (obesity, smoking, dietary intake, and physical activity) that met the definition of possible confounders into our analyses. As in other epidemiological studies on psoriasis,26-30 our diagnosis of psoriasis relied on self-reports of physician-diagnosed psoriasis, and we did not require an examination by a dermatologist. Previous validation studies in the NHS for another skin condition, basal cell carcinoma, found self-reports to be greater than 90% accurate.31-32 Furthermore, in the subset of confirmed psoriasis cases, we found a stronger association between risk of incident psoriasis and overall alcohol intake as well as nonlight beer intake.

In conclusion, our prospective study indicates that nonlight beer intake is associated with an increased risk of psoriasis, whereas light beer, wine, and liquor did not increase the risk among women. Specifically, women who drank at least 5 nonlight beers per week were 1.8 times more likely to develop psoriasis compared with women who abstained from alcohol. Lower intake of nonlight beer and intake of other types of alcoholic beverages do not appear to influence the risk of developing psoriasis. Women with a high risk of psoriasis may consider avoiding higher intake of nonlight beer. We suggest conducting further investigations into the potential mechanisms of nonlight beer inducing new-onset psoriasis.