Which one of these supplements has been shown to boost nitric oxide levels?

Cups Of Alcohol
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ANSWER: A. Caffeine. We bet this one fooled a lot of you. That’s because many guys are under the misconception that caffeine constricts blood vessels. However, it’s quite the contrary. Caffeine has been shown in research studies to boost blood flow to muscles by increasing nitric oxide levels and therefore dilating blood vessels. So don’t be afraid to take a dose of caffeine with your favorite NO booster, or to use an NO booster that has caffeine in it. To enhance blood flow to muscles during workouts for greater endurance and strength, take 200–400 milligrams of caffeine 30–60 minutes before workouts.