Psychology Department, Santa Barbara City College, Santa Barbara, CA, USA
Vitamins, particularly folate (vitamin B9), vitamins B6 and B12, and vitamins C, D, and E, are indispensable regulators of endothelial function, and their deficiency or insufficiency has been implicated in a broad range of vascular and degenerative disorders, including those affecting the pulmonary circulation. This narrative review synthesizes current evidence on the mechanisms by which vitamin status influences vascular health, with emphasis on folate metabolism, homocysteine regulation, and the clinical consequences of deficiency across systemic, retinal, cerebral, and pulmonary vascular beds. Folate is a central cofactor in one-carbon metabolism, supporting the remethylation of homocysteine to methionine. Elevated homocysteine impairs endothelial function through oxidative stress, reduced nitric oxide bioavailability, and accumulation of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase. These mechanisms are directly relevant to the pulmonary microvasculature: asymmetric dimethylarginine has been shown to predict the development of pulmonary arterial hypertension under hypoxic conditions, and severe vitamin B12 deficiency has been reported to produce pulmonary vascular congestion, edema, and hypoxemia. Cross-sectional data in elderly and chronic obstructive pulmonary disease populations further link lower serum folate and higher homocysteine to impaired spirometric parameters. Beyond homocysteine lowering, folate, particularly in its bioactive form, L-methylfolate, enhances nitric oxide production through regeneration of tetrahydrobiopterin, a cofactor for nitric oxide synthase. Clinical trials in patients with coronary artery disease demonstrate that supplementation improves flow-mediated dilation, a validated measure of endothelial function, at doses of 5 to 10 milligrams per day of folic acid. Evidence from retinal disease studies using medical-food doses of L-methylfolate with vitamins B12 and B6 shows reduction in homocysteine, restoration of capillary perfusion, and improved clinical outcomes in diabetic retinopathy, glaucoma, and age-related macular degeneration. However, excessive supplementation with synthetic folic acid raises concerns: it generates unmetabolized folic acid in the bloodstream, which may reduce cellular folate availability and is associated with increased cardiovascular mortality at high intake levels. Genetic polymorphisms in folate-metabolizing enzymes further affect individual responses to supplementation. Plasma homocysteine serves as a practical, low-cost biomarker for identifying patients likely to benefit from correction of folate and vitamin B12 status, with preference for bioactive reduced forms over synthetic folic acid. Prospective trials measuring pulmonary capillary perfusion and gas exchange before and after correction of vitamin insufficiency are warranted.
Keywords: Folate; Homocysteine; Vitamin B12; Endothelial Function; Nitric Oxide; Edema; Pulmonary Vascular Disease; L-Methylfolate
George Ayoub. “Optimizing Vitamin Status to Sustain Vascular and Pulmonary Health”. EC Pulmonology and Respiratory Medicine 15.7 (2026): 01-29.
© 2026 George Ayoub. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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