Alcohol Intake and Risk of Incident Psoriasis in US Women
A Prospective Study
Abrar A. Qureshi, MD, MPH; Patrick L. Dominguez, MD; Hyon K. Choi, MD, DrPH; Jiali Han, PhD; Gary Curhan, MD, ScD
Arch Dermatol. Published online August 16, 2010. doi:10.1001/archdermatol.2010.204
Objectives To evaluate the independent association between alcohol consumption and risk of developing psoriasis and to determine if this risk is associated with different types of alcoholic beverages.
Design A prospective study of female nurses who were followed up from 1991 to 2005.
Setting Nurses' Health Study II, a cohort of 116 671 US women aged 27 to 44 years in 1991.
Participants The study population included 82 869 women who reported amount and type of alcohol intake on biennial questionnaires. We excluded participants with a history of psoriasis prior to 1991.
Main Outcome Measure Self-report of incident physician-diagnosed psoriasis. For a sensitivity analysis, we had a subset of confirmed psoriasis cases.
Results There were 1150 cases of incident psoriasis, 1069 of which were used for analysis. Compared with women who did not drink alcohol, the multivariate relative risk (RR) of psoriasis was 1.72 (95% confidence interval [CI], 1.15-2.57) for an alcohol consumption of 2.3 drinks/wk or more. When examined by type of alcoholic beverage, there was an association between psoriasis and nonlight beer intake (multivariate RR for 5 drinks/wk, 1.76; 95% CI, 1.15-2.69); light beer, red wine, white wine, and liquor were not significantly associated with psoriasis risk. The association with nonlight beer intake became stronger in a subset of confirmed psoriasis cases (multivariate RR for 5 drinks/wk, 2.29; 95% CI, 1.36-3.85).
Conclusions Nonlight beer intake is associated with an increased risk of developing psoriasis among women. Other alcoholic beverages did not increase the risk of psoriasis in this study.
Psoriasis is a common immune-mediated skin disease.1-2 The association between alcohol consumption and increased risk of psoriasis onset and psoriasis worsening has long been suspected. For example, individuals with psoriasis drink more alcohol than individuals without psoriasis,3 and alcohol intake may exacerbate psoriasis severity.4 Case-control studies reported a significant association between alcohol consumption and psoriasis, but these studies retrospectively ascertained alcohol consumption. Furthermore, these associations showed a marked gender difference in men3, 5 and did not show a significant association between alcohol and psoriasis in women.6 One case-control study of alcohol intake and newly diagnosed psoriasis showed a dose response, but the findings were not significant after adjusting for cofactors.7
Alcohol may induce psoriasis via multiple mechanisms, including immunological changes such as keratinocyte proliferation8 and upregulation of proinflammatory cytokines.9 Other potential mechanisms include an increased risk of infection and mechanical trauma, which are well known to trigger psoriasis.10
Risk of psoriasis may vary depending on type of alcoholic beverage (ie, beer, wine, and spirits), as does the risk of other diseases, but no data are available on psoriasis. One prospective study confirmed, for example, that beer confers a larger risk of gout than spirits and wine.11 Risk for psoriasis may vary by type of alcoholic beverage, given previous evidence that different types of alcoholic beverages have conferred deleterious effects in other inflammatory diseases. If certain types of alcoholic beverages have different effects on risk of psoriasis, then this fact would have practical implications for psoriasis prevention and management.
We prospectively evaluated the association between total alcohol consumption and risk of incident psoriasis in a cohort of US women with no history of psoriasis. In this study, we also explored the association between type of alcoholic beverage and risk for incident psoriase
The Nurses' Health Study II (NHS II) is an ongoing longitudinal study of 116 430 female registered nurses from 15 states in the United States who were between the ages of 25 and 42 years when they completed and returned a baseline questionnaire in 1989.12-13 The cohort is followed with biennial questionnaires, and the follow-up rate exceeds 90%.
ASSESSMENT OF PSORIASIS
In 2005, NHS II participants were asked if they had ever received a physician diagnosis of psoriasis and if so, the date of diagnosis. Of the 82 869 participants who responded to the psoriasis question in 2005, 2430 women reported receiving a diagnosis of psoriasis; 1280 of these cases were prevalent at baseline in 1991 and 1150 incident cases occurred between 1991 and 2005. We started follow-up in 1991 because it was the first year for which we have information regarding alcohol intake. A total of 1069 women with incident psoriasis were included in this analysis.
We confirmed a subset of self-reports using the Psoriasis Screening Tool (PST) questionnaire.14 The PST is a 1-page self-administered questionnaire that assigns a diagnosis of psoriasis based on responses to 7 questions. The questions on the PST were derived from expert opinion and the National Psoriasis Foundation's survey on psoriasis. Three questions inquire about being diagnosed with psoriasis by some type of medical provider, such as a dermatologist, a primary care physician, or a nurse practitioner. Four questions inquire about having morphological skin changes of psoriasis, 3 of which are accompanied by pictures. Pictures were chosen to represent each of 3 common psoriasis phenotypes, namely plaques, nail changes, and scalp psoriasis. One nonpictorial question inquires about inverse psoriasis. Scoring algorithms were developed to assign a diagnosis of psoriasis depending on a participant's response to the questions. These scoring algorithms were based on multiple a priori hypotheses. A pilot study showed that the PST was able to screen for psoriasis with 99% sensitivity and 94% specificity14 in a population of adults attending an outpatient dermatology clinic of a tertiary care referral center. The PST has yet to be tested in a population with an expected low prevalence of psoriasis. However, using Bayes' theorem, we calculated the positive predictive value of the PST to be 25%. In other words, a positive test result on the PST increases the pretest probability of having psoriasis from 2% (assumed prevalence of psoriasis in the US population15-16) to 25%. We mailed the PST to all NHS II participants who self-reported a physician diagnosis of psoriasis and had an overall response rate of 87%.
ASSESSMENT OF ALCOHOL INTAKE
Information on alcohol intake was updated in 1995, 1999, and 2003. The 1991 questionnaire included questions on the average intake of alcoholic beverages (nonlight beer, light beer, red wine, white wine, and liquor) during the past year. Nurses responded to the following question: "For each food listed, fill in the circle indicating how often on average you have used the amount specified during the past year." Intake of each beverage was ascertained in 9 categories (number of drinks): none or less than once per month, 1 to 3 per month, 1 per week, 2 to 4 per week, 5 to 6 per week, 1 per day, 2 to 3 per day, 4 to 5 per day, and 6 or more per day. Total amount of alcohol consumed was estimated at 12.8 g for a glass, bottle, or can of beer (12 fl oz [360 mL]), 11 g for a glass of wine (4 fl oz [120 mL]), and 14 g for a shot of liquor (1.5 fl oz [45 mL]). Total alcohol intake was computed as the sum of the intake from beer, wine, and liquor. One drink was defined as 12.8 g of alcohol (median amount of alcohol in beer, wine, and liquor). Beverage-specific consumption was also calculated and analyzed separately. The reproducibility and validity of this questionnaire for alcohol intake have been previously documented in the NHS I cohort.17
ASSESSMENT OF COVARIATES
Date of birth and height were reported on the 1989 questionnaire. Participants reported their current weight,13 smoking status,12 dietary intake, and physical activity on the biennial mailed questionnaires. Quintiles of dietary folate equivalents (DFEs) were calculated from a validated semiquantitative food frequency questionnaire, and quintiles of metabolic equivalents (METs) were calculated from questions about various type of physical activity. Body mass index was calculated as weight in kilograms divided by height in meters squared. Previously, the accuracy of self-reported anthropometric measures was validated among 140 NHS I participants. Self-reported and measured weights were highly correlated (Pearson r = 0.97).18
We computed person-time of follow-up for each participant from the return date of the 1991 questionnaire to the date of diagnosis of psoriasis or the end of the study period. We used Cox proportional hazards regression models to estimate the age-adjusted and multivariate relative risk (RR) of incident psoriasis in women who reported alcohol intake compared with those who did not. We categorized alcohol intake into the following 6 categories: none, 1 to 4 g/wk, 5 to 9 g/wk, 10 to 14 g/wk, 15 to 29 g/wk, and 30 g/wk or more. We categorized type of alcoholic beverage (nonlight beer, light beer, red wine, white wine, and liquor) into the following 4 categories: none, 1 to 3 drinks/mo, 1 drink/wk, 2 to 4 drinks/wk, and 5 or more drinks/wk. We categorized body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) at baseline and at each questionnaire cycle into the following 6 categories: lower than 21.0, 21.0 to 22.9, 23.0 to 24.9, 25.0 to 27.4, 27.5 to 29.9, 30.0 to 34.9, and 35.0 or greater. We categorized DFE as low and high based on the median DFE. Median DFE was available only in 1999 and 2003. The median DEF was 976 µg in 1999 and 1000 µg in 2003. We applied the 1999 median DFE to the following 3 periods: 1991 through 1994, 1995 through 1998, and 1999 through 2002. We applied the 2003 median DFE to the 2003 through 2006 period. We explored potential interactions by DFE (high and low according to the period-specific median) by testing the significance of interaction terms added to our final multivariate models. For all RRs, we calculated 95% confidence intervals, and all P values were 2-sided. Statistical analyses were performed using SAS software, version 9.1 (SAS Institute Inc, Cary, North Carolina). The institutional review board of Partners Health Care System approved
Results There were 1150 cases of incident psoriasis, 1069 of which were used for analysis. Compared with women who did not drink alcohol, the multivariate relative risk (RR) of psoriasis was 1.72 (95% confidence interval [CI], 1.15-2.57) for an alcohol consumption of 2.3 drinks/wk or more. When examined by type of alcoholic beverage, there was an association between psoriasis and nonlight beer intake (multivariate RR for 5 drinks/wk, 1.76; 95% CI, 1.15-
We computed person-time of follow-up for each participant from the return date of the 1991 questionnaire to the date of diagnosis of psoriasis or the end of the study period. We used Cox proportional hazards regression models to estimate the age-adjusted and multivariate relative risk (RR) of incident psoriasis in women who reported alcohol intake compared with those who did not. We categorized alcohol intake into the following 6 categories: none, 1 to 4 g/wk, 5 to 9 g/wk, 10 to 14 g/wk, 15 to 29 g/wk, and 30 g/wk or more. We categorized type of alcoholic beverage (nonlight beer, light beer, red wine, white wine, and liquor) into the following 4 categories: none, 1 to 3 drinks/mo, 1 drink/wk, 2 to 4 drinks/wk, and 5 or more drinks/wk. We categorized body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) at baseline and at each questionnaire cycle into the following 6 categories: lower than 21.0, 21.0 to 22.9, 23.0 to 24.9, 25.0 to 27.4, 27.5 to 29.9, 30.0 to 34.9, and 35.0 or greater. We categorized DFE as low and high based on the median DFE. Median DFE was available only in 1999 and 2003. The median DEF was 976 µg in 1999 and 1000 µg in 2003. We applied the 1999 median DFE to the following 3 periods: 1991 through 1994, 1995 through 1998, and 1999 through 2002. We applied the 2003 median DFE to the 2003 through 2006 period. We explored potential interactions by DFE (high and low according to the period-specific median) by testing the significance of interaction terms added to our final multivariate models. For all RRs, we calculated 95% confidence intervals, and all P values were 2-sided. Statistical analyses were performed using SAS software, version 9.1 (SAS Institute Inc, Cary, North Carolina). The institutional review board of Partners Health Care System approved this study.
Over the 14-year follow-up period, 1069 incident cases of psoriasis occurred. There was no material difference in mean age between alcohol drinkers and abstainers (Table 1). Alcohol abstainers had a higher BMI and were less physically active. Proportion of current and past smokers was higher in alcohol drinkers, and dietary folate intake was higher in abstainers.
Table 1. Baseline Characteristics According to Alcohol Consumption Status
We observed an increased age-adjusted RR of psoriasis in women who consumed more than 2.3 alcoholic beverages per week compared with nondrinkers (Table 2). This risk remained significant after adjusting for age, BMI (both continuous and categorical), smoking, physical activity, and DFE. Although the RRs did not reach statistical significance in women who consumed less than 2.3 drinks per week, there was a significant trend toward increased risk for psoriasis with greater alcohol intake (P value for trend, .002).
Table 2. Age-Adjusted and Multivariate Relative Risks (RRs) for Incident Psoriasis by Amount of Alcohol Intake Among Women
We also found that the risk of psoriasis varied by type of alcoholic beverage. After adjusting for age, women who drank 5 or more nonlight beers per week had a greater RR of psoriasis (Table 3). The excess risk of psoriasis associated with consumption of at least 5 nonlight beers per week for all NHS II participants was 1.53%. We calculated the excess risk, which was: 106 per 100 000 Person-years (PY) – 46 per 100 000 PY = 60 per 100 000 PY. This gave an increase in RR of 1.3. This risk remained significant after simultaneously adjusting for age, BMI, smoking, physical activity, and DFEs. Women who drank any amount of light beer, white wine, red wine, or liquor were not at increased risk of incident psoriasis. We performed analyses with a common reference group that excluded any women who drank any type of alcohol and found no difference
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
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