To our knowledge, this is the first study to investigate the association between the frequency of AFH meals and inflammatory sinonasal diseases, such as AR and CRS. We analyzed the relationship by obtaining population-based real-world data representing the general population of South Koreans enrolled from 2010 to 2019 and creating logistic regression models [16]. The data not only contain general health characteristics collected with questionnaires from the participants but also features the clinical examination findings of nasal endoscopy. The otorhinolaryngology residents performed interviews and endoscopic examinations of each participant individually in a validated manner, according to clinical guidelines [15, 17, 18].
Our finding was that individuals having AFH meals more frequently had a higher risk for the diagnosis of both AR and CRS than those having AFH meals less frequently. Additionally, among the participants with AR, the endoscopic finding of watery rhinorrhea and the serum specific IgE level for house dust mites were associated with the frequency of AFH meals. Participants with CRS showed that, among the CRS symptoms, reduction of smell was associated with the frequency of AFH meals.
Several studies have investigated the potential clinical relevance of AFH meals in certain diseases. In a recent population-based study using the data of 35,084 participants from the National Health and Nutrition Examination Survey (NHANES), the hazard ratio of all-cause mortality was 1.49 (95% CI 1.05–2.13) for the participants who had AFH meals frequently compared to those who seldom ate AFH meals [19]. Another cross-sectional study that also used data from the NHANES analyzed the association between the frequency of eating AFH meals and biomarkers of chronic diseases [20]. The result showed that the mean BMI was higher, and serum concentrations of micronutrients such as vitamins B, C, D, and E, and α-carotene were decreased among the participants with more frequent AFH meals. Moreover, a study that investigated 723 subjects from Minnesota found that AFH meals were associated with being overweight [21].
Although no previous study has analyzed the association between AFH meals and AR or CRS, several factors can be considered to understand the positive relationship found in our study. Individuals who frequently consume AFH meals are deficient in several nutrients, including vitamin D, vitamin E, and folic acid [20]. Studies have reported a relationship between micronutrients and AR, and a meta-analysis concluded that high vitamin D concentration was associated with a lower prevalence of AR in adults, especially in men, and lower aeroallergen sensitization in children [22]. Another meta-analysis concluded that lower vitamin D levels are related to a higher prevalence of AR in children [23]. Regarding vitamin E, a study reported that treatment with vitamin E in an AR mouse model resulted in reduced AR symptoms and T-helper 2 cytokines [24]. Folic acid was also associated with the risk of AR; a shortage of maternal folic acid intake led to an increased risk of respiratory allergy in infants and children [25]. The aforementioned micronutrients are rich in vegetables, fruits, fish, nuts, and vegetable oil, which may not be abundant in AFH meals. Individuals who frequently consume AFH meals might be short of micronutrients, which have immunologic regulatory functions, such as Th2 response inhibition [26].
Similar results have been reported in the literature for CRS. In a recent study, primary human nasal epithelial cells from patients with CRS with nasal polyps were collected and treated with lipopolysaccharide, followed by calcitriol, the active form of vitamin D [27]. The results showed that the production of interleukin (IL)-6 was alleviated and phosphorylation of p65, which represents the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, was significantly decreased.
Regarding the possible theory of the association between AFH meals and watery rhinorrhea symptoms in patients with AR, an animal study applied topical retinoic acid (vitamin A) to the maxillary sinus mucosa of rabbits [28]. The authors found that the topical vitamin A group showed enhanced regeneration of damaged paranasal mucosa, including submucosal gland loss, compared to the control group without vitamin A application. Sensitization to house dust mites might be related to the frequency of AFH meals owing to the lack of vitamin D. A recent study evaluated the vitamin D status of patients with atopic dermatitis sensitized to house dust mites and found that there was a negative correlation between specific IgE for house dust mites and serum vitamin D levels [29].
This study has some limitations. Due to its cross-sectional design, it is unable to clearly define the causal relationship between AFH meals and AR or CRS. In addition, the types of food or nutrients that the study participants had consumed were not included in the analysis. KNHANES data included the usual type of food that the participants took daily. However, the questionnaire for food type has not been consistently organized during the 10-year survey duration, making it difficult to quantify which foods or nutrients should be taken into account. Thus, we used the frequency of AFH meals as an independent variable. As AFH meals grow more popular, further research, such as a prospective study regarding what type of food or nutrients affect AR or CRS, may help understand the association between AFH meals and AR or CRS.