Serum Homocysteine Levels and All-Cause and Cause-Specific Mortality in Korean Adult Men: A Cohort Study

Background: Hyperhomocysteinemia can increase the risk of cardiovascular disease (CVD), cancer, and neurological disorders; however, hypohomocysteinemia is generally not considered harmful. This study aimed to evaluate the relationship between all levels of homocysteine, both low and high homocysteine levels, and the risk of all-cause and cause-specific mortality in adult Korean men. Methods: Adult Korean men (n = 221,356) were categorized into quintiles based on their homocysteine levels. The primary endpoints were all-cause, CVD, cancer, and dementia mortality. Hazard ratios were calculated using Cox proportional hazards models, and the dose-response relationship between homocysteine levels and mortality risk was further explored using restricted cubic spline models. Results: Compared with the reference category (Q2, 8.8-9.9 mu mol/L), there was a significant increase in all-cause mortality associated with both low and high levels after multivariable adjustment (Pinteraction = 0.002). Additionally, in spline regression, a U-shaped association between homocysteine levels and all-cause and CVD mortality was observed (inflection point = 9.1 mu mol/L). This association was not observed in the vitamin supplementation subgroup. Conclusion: Among Korean adult men, both low and high homocysteine levels increased the risk of all-cause and CVD mortality, indicating a U-shaped relationship. However, this relationship was not statistically significant with vitamin supplementation, suggesting a potential protective role for vitamins.