If you’re referring to a vitamin associated with blood-vessel dilation and circulation, the answer is often vitamin B3 (niacin).
How niacin affects blood vessels
Niacin can cause vasodilation, particularly in the skin, by increasing blood flow to small blood vessels. This can produce the familiar “niacin flush”—warmth, redness, itching, or tingling.
However, there’s an important distinction:
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Niacin treats vitamin B3 deficiency and has legitimate medical uses.
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Taking high-dose niacin just to improve circulation isn’t generally recommended. It can cause flushing, low blood pressure, liver problems, elevated blood sugar, and other adverse effects.
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Niacin supplements should not be used as a substitute for treatment of poor circulation or cardiovascular disease.
If by “improves circulation” you mean cold hands/feet, leg pain when walking, erectile problems, or diagnosed blocked arteries, the appropriate treatment depends on the underlying cause rather than simply taking a vitamin.
