Vitamin A Intake and Risk of Cancer Incidence: Insights from a Case-Control Study.

Background: The association between dietary vitamin A intake and cancer risk remains unclear. There may be under-researched links between dietary vitamin A and cancer. This study aimed to clarify this relationship and a possible reference vitamin A intake. Methods: We conducted a hospital-based case-control study. Exposure data was determined from participants, including 3758 incident cancer cases (esophagus, stomach, colon, rectum, lung, breast, and other cancers) and 2995 hospital controls before the day of surgery treatment at the same hospitals. Dietary vitamin A intake was assessed using a validated semi-quantitative food frequency questionnaire. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to evaluate the association between vitamin A intake and cancer risk. Restricted cubic splines suggest a safe range of vitamin A intake of 85.3-104.0 µg/day, which is a reference quantile. Results: We found a U-shaped association between vitamin A intake and cancer incidence compared to the reference. Both the lowest and highest intakes were associated with an increased cancer risk, with OR (95% CI) values 1.98 (1.57, 2.49) and 2.06 (1.66, 2.56), respectively. This U-shaped pattern was consistent across subgroups defined by sex, body mass index, smoking status, alcohol consumption, blood type A, and cancers of the esophagus, stomach, breast, and rectum, but not lung and colon cancer. The U-shaped relationship remained after adjusting for dietary vitamin A intake per kg of body weight and vitamin A-energy residual estimation adjustment. Confidence intervals were wider at the highest exposure levels. Conclusions: We observed a U-shaped relationship between vitamin A intake and the risk of cancer incidence, with a reference dietary vitamin A intake of 85.3-104.0 µg/day. These findings warrant further investigation to understand the mechanisms of this U-shaped association.