Vitamin A Insufficiency in Current and Former Smokers and Lung Cancer Risk: A Case-Control Approach

Abstract

Background: Adequate dietary intakes of vitamin A are protective against lung cancer, but little is known about the risk of lung cancer when intakes of the vitamin are below minimum physiological requirements. Further investigation into this relationship is needed considering established relationships between smoking, vitamin A deficiency (VAD), and lung cancer risk. Objective: The objective of this study was to determine whether intakes of vitamin A below the minimal physiological threshold increased the likelihood of lung cancer. We hypothesized vitamin A intakes above the minimal physiological threshold would reduce the likelihood of lung cancer. Methods: A case-control approach was used, utilizing data from eight cycles of NHANES surveys. Cancer-free, everyday cigarette smokers were matched on a 1:1 basis to cases with lung cancer by smoking duration, sex, and age. Paired sample T-tests were used to test differences in mean intakes of retinoids between groups, while an Exact McNemar test was used to assess differences between categorical variables. Conditional logistic regression was used to model the relationship between vitamin A insufficiency and lung cancer incidence, before and after adjustment. Results: A covariate in our adjusted model, milk consumption was significantly associated with increased odds of lung cancer (OR = 2.38, CI = 1.04 – 5.43). Contrary to our hypothesis, intakes of vitamin A at or above the minimal physiological threshold increased the odds of lung cancer, though confounding effects of several covariates, such as the age of smoking initiation, could not be ruled out (OR = 5.49, CI = 0.82 – 36.96). Conclusions: While mean intakes of vitamin A and subtypes did not significantly differ between case and control, only 20.4 % of individuals across our sample consumed intakes at or above gender-specific RDAs. As we did not collect data on food-specific micro/macronutrients, more research into dietary contributions of micro/macronutrients from foods known to be implicated in lung cancer prevention or risk, such as vitamin A, vitamin A, calcium, and fatty acids, could prove to be important areas for future research.