Interactive effects of folate and methylmalonic acid on cardiovascular disease mortality: Epidemiological and experimental evidence

Folate shows paradoxical associations with cardiovascular disease (CVD), and its interaction with methylmalonic acid (MMA) may contribute to this risk. We examined the independent and interactive effects of MMA on CVD mortality using data from 22,487 NHANES participants (1999-2014). Over 12.1 years of follow-up, 1,510 CVD deaths occurred. Restricted cubic splines showed a U-shaped association between folate and CVD mortality and a linear association for MMA. Both low and high folate were linked to was linked to increased mortality only when MMA exceeded 182 nmol/L, with significant additive interaction. <i>In vitro</i>, MMA amplified folate-induced cytotoxicity in H9c2 cardiomyocytes, reducing viability to 49%, while transcriptomic analysis identified 53 inflammation-related genes under combined exposure. These findings provide both epidemiological and mechanistic evidence that elevated folate and MMA independently and synergistically worsen cardiovascular outcomes, highlighting the importance of considering functional B-vitamin status in risk assessment and public health strategies.