If you mean one vitamin that can actually cause blood-vessel widening, the best-known example is vitamin B3 (niacin).
Vitamin B3 (Niacin)
Niacin, specifically nicotinic acid, can cause vasodilation of small blood vessels near the skin. This produces the familiar “niacin flush”—warmth, redness, tingling, and sometimes itching. The flushing occurs because of increased blood flow in those vessels. ODS+1
However, there is an important distinction:
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Niacin does open certain blood vessels temporarily, but that does not mean taking niacin supplements is a proven way to improve overall circulation.
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The usual nutritional requirement for adults is only about 14–16 mg/day. ODS
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Doses high enough to produce a noticeable flush can cause low blood pressure, dizziness, headaches, elevated blood sugar, and liver problems. The NIH lists 35 mg/day as the adult upper limit for supplemental niacin for healthy people, although medically supervised treatment can use much higher doses. ODS
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Niacinamide (nicotinamide) is different—it generally doesn’t cause the vasodilating flush. ODS
Does niacin improve poor circulation?
Not necessarily. If someone has genuinely reduced circulation—for example, leg pain when walking, cold feet, numbness, or known peripheral artery disease—taking niacin on your own isn’t an established treatment. The 2024 ACC/AHA guideline specifically notes that there isn’t compelling evidence that vitamin supplementation reduces major cardiovascular events in peripheral artery disease. American Heart Association Journals
So I wouldn’t recommend taking high-dose niacin simply to “open the blood vessels.”
If you tell me what you mean by poor circulation (e.g., cold hands/feet, erectile blood flow, leg circulation, numbness/tingling, or general cardiovascular health), I can explain which vitamins, foods, or treatments actually have evidence for that particular problem.
