If you mean the popular claim “one vitamin that opens blood vessels and improves circulation,” the closest match is niacin (vitamin B3)—but the claim needs an important qualification.
Vitamin B3 (niacin)
Niacin, specifically nicotinic acid, can cause temporary vasodilation and skin flushing. This happens because blood vessels near the skin widen, producing warmth, redness, tingling, or itching. (ODs)
However, niacin supplements should not be used simply to “improve circulation.” High-dose niacin can cause side effects and, despite improving some cholesterol numbers, has not been shown to reduce cardiovascular events when added to appropriate treatment. Current cardiovascular guidance does not recommend routinely adding niacin for this purpose. (ODs)
For overall circulation and cardiovascular health, the stronger evidence supports regular physical activity, not smoking, maintaining a healthy weight, controlling blood pressure and cholesterol, and eating a heart-healthy diet. (professional.heart.org)
Bottom line: Vitamin B3 can temporarily widen some blood vessels, but it’s not a general-purpose circulation treatment, and high-dose supplements shouldn’t be taken without medical advice.
