By Dr. Brian McDonough, Medical Editor

PHILADELPHIA (CBS) – Millions of Americans do it every day. Wake up early. Grab a cup of coffee and get some sort of workout. But is that a mistake?

Researchers suggest the amount of caffeine in just two cups of coffee can cut down the body’s ability to increase blood flow to the heart during exercise. Now this means that vital blood flow to the heart can be cut back when the body needs it most.

It is interesting that caffeine did not affect heart blood flow when the participants were inactive. Caffeine may block certain receptors in the walls of blood vessels interfering with the normal signaling processes that cause blood vessels to dilate in response to exercise. It might make sense to exercise before that cup of joe.

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