Introduction
Pemphigus vulgaris (PV) is a chronic autoimmune disease with blisters and inflammation.1 In PV, autoantibodies target desmosome components, which ultimately lead to the formation of intraepithelial blisters by reducing intercellular adhesion between keratinocytes.2 The global prevalence of PV was reported at 2.83 per million person-years.3 The incidence of this disease in Iran was 5 per 100 000 annually, with a male-to-female ratio of 1:1.6.4 Iran accounted for approximately 19% of the reported documented cases of PV globally.5 Symptoms and severity of PV vary from person to person. The diagnosis of bullous skin diseases is made based on the skin manifestations and characteristic direct immunofluorescence (DIF) patterns on skin biopsies.6–8 Initially, the goal of PV treatment is focused on the control of the disease (reduce functional impairment and heal vesicular skin and mucosal lesions).9 There are several mediators in the network of disease pathophysiology, including genetic and environmental factors. Interaction between genetic predisposition and environmental factors can lead to the onset and recurrence of the disease, such that older age of onset,10–13 delayed initiation of corticosteroid therapy,14 comorbidities15 and the nutritional status1617 of these patients have a significant effect on the severity of the disease.
Diet, one of the most modifiable risk factors affecting PV, can play a role in the development of autoimmunity.1819 A healthy diet boosts the immune system in presenting antigens and distinguishing abnormal proteins.20 Various food groups contain some PV simulators such as thiols, phenols, tannins and anthocyanins. Nuts are among the dietary food groups, containing high-risk dietary factors. Nuts can affect the severity of PV disease due to their content of organic chemical compounds, including tannic acid, vitamins such as vitamin B3 and various minerals such as copper.21 Consuming nuts can have contrasting effects on PV due to the different compounds they contain.
The tannic acid in nuts initiates PV and increases its severity, especially in genetically predisposed patients.2021 On the other hand, studies have also shown that serum concentrations of copper, zinc and selenium are lower in patients with PV than in healthy individuals, which may contribute to the exacerbation of painful oral lesions or chronic inflammation.22–24 However, as these minerals are found in nuts, they might protect against PV. Due to these dual effects and controversial findings, the association between nut intake and PV initiation and progression is unclear. Given these findings, a higher rate of PV in Iran and also higher dietary intakes of nuts among this population, we conducted this cross-sectional study to investigate the relationship between nut consumption and disease severity based on the Pemphigus Disease Area Index (PDAI) score.
Considering the significant impact of diet, including nuts, due to the presence of different nutrients and their opposing effects on disease severity, we designed this study on PV patients.
Method and material
Study and population
In 2021, a cross-sectional study was conducted in a hospital among patients diagnosed with PV. The adult PV patients identified for 2 months are sent to the pemphigus clinic at Razi Hospital, a specialist institution for skin disorders in Iran. A pathologist at the Pemphigus Clinic at Razi Hospital verified the diagnosis of PV.
The quantity of samples was determined using the following formula:
N=[(Zα+Z1−β)/0.05 ln1+r/1−r)]2+3; considering r=0.30, 1−β=0.95 and α=0.05, also considering type I and type II error of 0.05.
All 138 adult PV patients, irrespective of gender, were included. Participants were individuals with pathological confirmation of PV who were between the ages of 18 and 65. The diagnosis of PV was based on clinical findings (mucosal and/or skin bullae/erosions), pathological reports (suprabasal cleft and acantholysis), DIF findings (intercellular IgG and/or C3 deposits) and the presence of serum anti-desmoglein 3.
Participants must be ambulatory individuals with a caloric consumption between 800 and 4200 kcal, have a clear diagnosis of PV illness, be between the ages of 18 and 65, smoke now or previously and have stable disease. The following were excluded: individuals with a history of inflammatory illness, low or high total calorie intake (<800 or >4200 kcal/day), malignancy issues, migration, pregnancy, breastfeeding and a consultation with a dietician within the previous year.
Evaluation of nutritional consumption
The habitual dietary intake of PV patients over the last year of study enrolment was assessed using a validated semi-quantitative food frequency questionnaire (FFQ). The questionnaire included 168 standard portion food items that are commonly consumed in Iran.25 The questionnaire was administered through a face-to-face interview conducted by a trained nutritionist. Participants reported the average frequency of consumption for each of the 168 foods per week or day over the preceding 12 months.
Serving sizes were converted to grams using home measurements. The consumption in grams of each food item was converted to daily intake by dividing the weight of each food item consumed by the corresponding time factor (eg, once a month divided by 30 and once a week divided by 7). In this study, a single general practitioner (GP) conducted the patient interviews.
The patients were enrolled in the study during a single season, and the results did not exhibit seasonal variations. This study aimed to minimise bias effectively. The average daily energy, macronutrient and micronutrient intakes of the participants were calculated using the latest version of the Dietitian IV software (V.7.0; N-Squared Computing, Salem, Oregon, USA), specifically designed for evaluating Iranian foods.
Evaluation of disease severity
This study assessed disease severity using the PDAI scoring system, established by the International Pemphigus Definition Committee. The validity and reliability of the PDAI score have been established in adults. The potential range of PDAI is from 0 to 26 342.
Of the total 263 points, 250 points are allocated to disease activity, comprising 120 points for skin activity, 10 points for scalp activity and 120 points for mucosal activity. Additionally, 13 points are designated for lesion-disease activity related to post-inflammatory hyperpigmentation. The severity of pemphigus was evaluated through observation and physical examination conducted by a trained dermatology assistant.
Following the calculation of each patient’s PDAI score, determined by the quantity and dimensions of lesions across various anatomical regions, patients were categorised into two groups. Based on prior research, participants were classified into moderate (PDAI 15 or less) and severe (PDAI 15 or more) categories.
Evaluation of additional variables
Data regarding participants’ general characteristics, medical history and lifestyle variables were collected through a general questionnaire. This included continuous variables such as age and duration of disease, as well as categorical variables such as sex (male/female), marital status (single/married), education level (under university/university graduated), high-risk job status (exposed to chemicals/not exposed), corticosteroid use (less than 5 mg per day/more than 5 mg per day of prednisolone), smoking status (people who smoke/people who do not smoke) and cumulative dose of rituximab. Additionally, information was gathered on any history of chronic diseases, including diabetes, hypertension, cardiovascular disease, hyperlipidaemia, cancer, hypothyroidism, non-alcoholic fatty liver disease, polycystic ovary syndrome, viral infections and family history of these diseases.
A trained GP collected anthropometric parameters following WHO guidelines. Weight was measured to the nearest 100 grams while participants wore light clothing and no shoes, using a digital scale (SECA, Hamburg, Germany). Height was recorded to the nearest 0.1 cm with a non-elastic tape measure, taken in a standing position next to a wall, ensuring the patient’s shoulders were in a neutral position and barefoot.
Waist circumference was assessed with a non-stretching tape measure positioned between the lower rib and the midpoint of the sternum. The calculation of body mass index (BMI) involved dividing the patients’ weights by the square of their heights (kg m2). Blood pressure was measured by a single individual using a standard-sized sphygmomanometer cuff and a stethoscope.
Measurements were taken from both arms of the patient after a resting period of at least 5 min, with the patient in a fully seated position. Blood tests, such as lipid profile and blood sugar, necessitate fasting for 8 to 12 hours. The assessment of physical activity used the International Physical Activity Questionnaire, which quantified physical activity as metabolic volume multiplied by time per day and categorised it into mild, moderate and intensive levels.26
Dietary nut evaluation
Dietary intakes were assessed using a valid 168-item FFQ, and the quartiles of total nut and their stratified types such as peanut, hazelnut, almonds, walnuts and pistachio intakes were calculated.
The nut score was categorised into quartiles before analysis. Categorical variables were presented using numerical values and percentages. Continuous variables were reported as mean±SD/SE.
The Kolmogorov-Smirnov test was employed to assess the normality of test variables. Patients were categorised based on their PDAI and nut scores. Independent t-tests were employed for continuous qualitative variables, while χ2 or Fisher’s exact tests were used for ordinal variables to compare general characteristics and nutritional intakes across two categories of PDAI scores.
One-way analysis of variance (ANOVA) and χ2 or Fisher’s exact tests were employed to compare these characteristics across the nut quartiles. The relationship between total nut and its components with disease severity risk, as measured by PDAI score components, was examined using binary logistic regression in both crude and adjusted models. PDAI was coded as a dummy variable (PDAI=15 = 0, PDAI>15 = 1) and used as the dependent variable (Y) in the regression model.
In all multivariate models, Q1 of the nuts score served as the reference category. Logistic regression was employed in both crude and adjusted models to investigate the association between the nuts score and the severity of skin and mucous membrane involvement. Age (continuous) and sex (male/female) were regarded as confounders in the initial model.
The continuous control of energy intake was implemented in the second model. The third model incorporated BMI. In the final model, tobacco use (yes/no), university education (yes/no), corticosteroid use (≤5 mg/>5 mg) and physical activity level (mild/moderate) were incorporated as additional co-factors from the preceding models.
A statistical analysis was conducted using SPSS software (SPSS Inc, Chicago IL—V.22.0), with a significance threshold set at a p value of less than 0.05.
Results
Table 1 presents the demographic characteristics of patients across different PDAI categories and quartiles of nuts consumption. Patients with higher disease severity (PDAI>15) had significantly lower doses of corticosteroids and rituximab, as well as shorter disease duration. Conversely, these patients exhibited higher serum triglyceride levels.
When patients were categorised based on nuts consumption quartiles, those in the highest quartile had significantly longer disease duration. Additionally, corticosteroid usage differed significantly among the four groups. No significant differences were observed between PDAI groups or nuts consumption quartiles for other demographic variables (p>0.05).
Table 2 summarises the dietary intakes of participants across nuts consumption quartiles and PDAI scores. Patients with higher PDAI scores had significantly lower intakes of vitamin C and total fibre (including both soluble and insoluble types) compared with those with lower PDAI scores. Interestingly, these patients had higher dietary cholesterol intake.
Analysis by nuts consumption quartiles revealed that individuals in the highest quartile had the highest intakes of calories, total fat, monounsaturated fatty acids, oleic acid, phosphorus, zinc, copper, potassium, vitamin A and water-soluble vitamins (B2, B5, B6, B9 and C), as well as both soluble and insoluble fibre in comparison to lowest quartiles. Notably, these participants also had relatively high intakes of beta-carotene and alpha-tocopherol. No significant differences were found in other dietary variables.
Table 3 displays the multivariable-adjusted ORs and 95% CIs for the association between nuts consumption and PDAI scores. In the crude model, nuts consumption was associated with a 93% lower risk of severe PV (OR=0.07; 95% CI 0.01 to 0.38; p for trend=0.000). After adjusting for sex and age, participants in the highest quartile had a 92% lower likelihood of severe disease compared with those in the lowest quartile (OR=0.08; 95% CI 0.01 to 0.40; p for trend=0.000).
This association remained strong after further adjustment for energy intake (OR=0.07; 95% CI 0.01 to 0.36; p for trend=0.000). The association was further strengthened after controlling for education, physical activity and smoking (OR=0.07; 95% CI 0.01 to 0.38; p for trend=0.000). In Model 4, after adjusting for corticosteroid use, the association persisted (OR=0.08; 95% CI 0.01 to 0.43; p for trend=0.001).
Finally, after additional adjustment for fibre intake, the association remained statistically significant (OR=0.12; 95% CI 0.02 to 0.69; p for trend=0.012).
Discussion
The findings showed that individuals with the highest total nut intake, including almonds, pistachios, peanuts, walnuts and hazelnuts, experienced less PV severity than individuals with the lowest intake. After adjusting for the effects of the confounders, including age, sex and energy intake remained significant. However, after adjusting for the effects of corticosteroid use and physical activity, there was no significant difference in the association between higher nut consumption and disease severity.
Stratified analyses of nut subtypes showed no association with PV severity.
People who eat more nuts like pistachios and peanuts often have the habit of sucking their shells, which contain a lot of tannins, which makes them more prone to PV induction.27 Although we found a significant inverse relationship in the crude models with the severity of PV, previous findings are exactly the opposite.
Adherence to a high Alternate Healthy Eating Index (AHEI)-2010 score, which is associated with higher nut consumption, reduces the severity of PV compared with individuals with a lower AHEI-2010 score, resulting from lower nut consumption.16 Another study that identified nuts containing tannin as high-risk nuts also showed that using less of it could lead to an improvement in the severity of PV.28 Nicotinamide, found in nuts, may be effective in treating bullous pemphigus when combined with minocycline.29–32 The potassium in nuts improves the regulation of cell osmotic pressure, maintains water and electrolyte balance and supports the metabolism of proteins and carbohydrates.2133 Higher content of copper and zinc in nuts is protective. Particularly, the serum levels of these minerals are low in PV patients.34 Given that serum copper concentrations are low in PV patients with poor nutrition combined with painful lesions in the oral cavity or chronic inflammation, it is possible that nuts, which are a good source of copper, may help these patients, although data are limited.212333 The findings of the study suggest that individuals with psoriasis are less likely to adhere to the Mediterranean diet than controls.19 Also, in another study, adherence to a Mediterranean diet, which is associated with high consumption of nuts, can reduce psoriasis severity.35 On the other hand, a study showed that a higher polyunsaturated fatty acid/saturated fatty acids (PUFA/SFA) ratio, which could be due to lower nut consumption, was not significantly associated with PV severity.36 Some food allergens, such as peanuts and tree nuts, can exacerbate atopic dermatitis, especially in children, by increasing IgE levels and provoking anaphylaxis.37–39
During chronic inflammation, such as in pemphigus, the body’s antioxidant defence system gradually weakens and cannot neutralise the produced reactive oxygen species, and thus, oxidative stress occurs.40 In oxidative stress, the rate of lipid peroxidation increases, and the amount of enzymatic and non-enzymatic antioxidants decreases.4142 Given that diet can directly influence lymphoid organs and immune cells (most of which are found in the gastrointestinal tract) from the time of embryogenesis onwards, some mechanisms could explain this. Nuts, which contain unsaturated fats, may help reduce concentrations of inflammatory markers.43 Omega-3 fatty acids found in nuts such as walnuts can provide a substrate for the synthesis of pro-inflammatory group 5 leukotrienes and group 3 prostaglandins, ultimately reducing insulin-like growth factor 1 levels and follicle inflammation.44–47 Magnesium, a mineral found in nuts, may reduce inflammatory markers.48 Nuts are also a good source of polyphenols, which may modulate signalling pathways through their anti-inflammatory properties.49 α-Linolenic acid has beneficial effects on cytokine production, leading to a reduction in molecules responsible for cell adhesion, including E-selectin.50 It can also inhibit inflammatory biomarkers and endothelial activation.51 Nut consumption may be associated with reduced actinic skin damage.52
Our study has several strengths: this is the first study to examine the association between the consumption of different nut subtypes and PV development, taking into account confounding variables, and the findings, which were conducted in a population of Iranian patients with PV, provide valuable information about one of the important dietary food groups, namely nuts, in this disease, due to the rare nature of this disease. This study, like any other study, has limitations. Due to the cross-sectional design, it cannot be clearly explained as a cause-and-effect relationship.
Our database was extracted from FFQ, which may be subject to underreporting or overreporting, which could bias the conclusions. There was also a possibility of selection bias in the diagnosis and selection of PV patients by dermatologists. We did not have the necessary economic information of the participants regarding the availability of nuts in the diet.
Considering all these issues, this study is the first to investigate the relationship between nut consumption and disease severity based on the PDAI score in PV patients in Iran.
Conclusion
The findings of this study suggest a negative association of nut consumption with PV severity as measured by PDAI. However, this association was not demonstrated in the nut subgroups in the stratified analyses. Finally, prospective cohort studies are needed to confirm these findings.