Diet Quality and Non Melanoma Skin Cancer Among U.S. Adults: A Cross-Sectional Analysis of NHANES 1999-2026

Background Non-melanoma skin cancers (NMSC), including basal cell carcinoma and squamous cell carcinoma, are the most common malignancies in the United States. Although ultraviolet (UV) radiation is the primary environmental risk factor, systemic factors may influence susceptibility to UV-induced carcinogenesis. Dietary factors may affect oxidative stress, inflammation, immune function, and DNA repair, all of which contribute to cutaneous carcinogenesis. We investigated the association between overall diet quality and odds of NMSC among U.S. adults. Methods Adults aged ≥20 years from nine National Health and Nutrition Examination Survey (NHANES) cycles spanning 1999-2016 were included if complete dietary, demographic, and dermatologic data were available. Diet quality was assessed using a modified Alternative Healthy Eating Index (AHEI) composite score and evaluated both continuously and by tertiles (low, medium, and high). NMSC was defined by self-reported physician diagnosis (MCQ220). Survey-weighted logistic regression models estimated adjusted odds ratios (ORs) for NMSC, controlling for age, sex, race/ethnicity, education, BMI, and sun exposure. Dietary sample weights (WTDR2D) were incorporated to generate nationally representative estimates. Results Among 32,243 participants, higher AHEI scores were associated with lower odds of NMSC. When modeled continuously, each one-unit increase in AHEI was associated with a 1.1% reduction in the odds of NMSC (OR, 0.989; 95% CI, 0.980-0.998; p=0.0146). A similar gradient was observed across AHEI tertiles compared with the lowest tertile, with lower odds among participants in the medium (OR, 0.844; 95% CI, 0.728-0.978; p=0.024) and high (OR, 0.804; 95% CI, 0.690-0.937; p=0.0056) tertiles. Participants in the highest tertile had approximately 20% lower adjusted odds of NMSC than those in the lowest tertile. Discussion In this nationally representative sample, greater adherence to a healthier dietary pattern was associated with progressively lower odds of NMSC. This relationship may reflect the potential effects of antioxidant and anti-inflammatory dietary components on UV-induced oxidative stress, DNA damage, and immune-mediated tumor surveillance. However, the cross-sectional design precludes causal inference. Healthier dietary behaviors may also correlate with greater healthcare utilization, potentially influencing the likelihood of receiving or reporting an NMSC diagnosis. Residual confounding, including cumulative UV exposure, occupation, and genetic susceptibility, and potential misclassification of self-reported NMSC remain possible. Additionally, the modified AHEI used in this analysis was based on nutrient-level components rather than complete food-based scoring. Conclusions Higher diet quality was independently associated with lower odds of NMSC among U.S. adults. These findings support further investigation into dietary patterns as potentially modifiable factors in skin cancer prevention and the biologic mechanism underlying the relationship between nutrition and UV-induced carcinogenesis.