Association between vitamin B6 metabolism and the prevalence of age-related macular degeneration: A cross-sectional analysis of National Health and Nutrition Examination Survey (NHANES)

B vitamins may be involved in the development of age-related macular degeneration (AMD). This investigation intended to examine the association between vitamin B6 catabolic status and the prevalence of AMD. Individuals ≥ 40 years old in the 2005 to 2008 National Health and Nutrition Examination Survey who had complete vitamin B6 measurement and AMD diagnostic data were included in this cross-sectional study. The catabolic status of vitamin B6 was evaluated using serum levels of pyridoxal 5'-phosphate (PLP) (the active form) and its metabolite 4-pyridoxic acid (4-PA). The analysis of 4-PA, PLP, and the 4-PA to PLP ratio (4-PA/PLP) used continuous variables and quartiles (Q1-Q4). The associations of 4-PA, PLP, and 4-PA/PLP with the prevalence of AMD were evaluated via weighted logistic regression, with odds ratio (OR) and 95% confidence interval (CI) estimates provided. Nonlinear relationships were explored utilizing restricted cubic splines. Of these 4202 included individuals, 549 were diagnosed with AMD and 3653 were non-AMD patients. High PLP levels (Q4 [≥ 55.475 nmol/L] vs Q1: OR [95% CI] = 0.69 [0.48-0.97]) were significantly associated with lower odds of AMD, whereas high 4-PA/PLP levels (Q3 [0.668-0.976]: OR [95% CI] = 1.57 [1.07-2.29]; Q4 [≥ 0.976]: OR [95% CI] = 2.00 [1.35-2.96]) were related to higher odds of AMD. The associations of PLP levels (Q4: OR [95% CI] = 0.49 [0.32-0.76]) and 4-PA/PLP levels (Q4: OR [95% CI] = 2.18 [1.27-3.75]) with the prevalence of AMD were observed only in individuals aged ≥ 65 years and not in those aged < 65 years. No significant association was found between 4-PA levels and the odds of AMD (P > .05). The restricted cubic splines curves demonstrated that the nonlinear relationships of 4-PA (Poverall = .002; Pnon-linear = .730) and PLP (Poverall < .001; Pnon-linear = .791) with the prevalence of AMD were not significant, whereas the levels of 4-PA/PLP (Poverall < .001; Pnon-linear < .001) had a significant nonlinear association with the prevalence of AMD. High 4-PA/PLP levels showed an association with high odds of AMD, suggesting that vitamin B6 catabolic status may influence the prevalence of AMD.