Supplements and prescription drugs that dilate blood vessels are called vasodilators. Vasodilators relax muscles that press against blood vessels, thereby allowing those vessels to expand. Doctors prescribe vasodilators mainly to combat heart-related ailments such as high blood pressure, but improvements in circulation also promote general health. You can also get similar results using dietary supplements, and with fewer side effects.
Magnesium is a mineral that works in the same way as calcium channel blockers prescribed by physicians for hypertension and angina (pain caused by insufficient blood flow to the heart muscle). Too much calcium in the blood constricts vessels, causing the heart to work harder to maintain a constant blood supply to bodily tissues. Magnesium blocks calcium and negates its constricting effect, but it also increases the body's own production of nitric oxide, which naturally widens blood vessels.
Hawthorne is a relatively inexpensive herbal supplement that acts as a vasodilator affecting, primarily, the coronary vessels. In addition to increasing blood flow by dilating major vessels, Hawthorne appears to directly benefit those suffering from heart damage. Its benefits are not immediate, however, but occur over time.
Vitamin C has probably undergone more scientific scrutiny than any other supplement, partly because of its long-standing status as an antioxidant, a substance that protects against cell damage perpetrated by the "free radicals" associated with ageing. Less public is the evidence that vitamin C seems to reduce "endothelial dysfunction," a condition that prevents dilation of blood vessels and can lead to hardening of the arteries (atherosclerosis).
Vitamin B-3, also known as niacin, creates the most dramatic example of blood vessel dilation of all the supplements listed here. In higher dosages, this supplement causes "niacin flush," a tingling redness of the skin resulting from a burst of histamines after ingestion. The flush lasts 10 to 20 minutes, and is harmless and probably helpful because of the increase in blood flow it causes. However, some people find it uncomfortable. In addition to dilating vessels and increasing blood flow, this vitamin appears to lower LDL cholesterol and raise the "good," HDL cholesterol.
You should always consult a health professional before taking supplements. Using herbal supplements is especially risky when combining them with prescription drugs, as herbs sometimes duplicate a drug's effect. Also, unlike prescription drugs, supplements are less regulated and may contain more or less of the active ingredient than the bottle states.