Regular exercise is known to be good for heart health, but the risk of a heart attack temporarily increases during an exercise session. Most heart attacks and strokes are caused by a blood clot that disrupts blood flow to the brain or heart. During exercise, there is an increase in the amount of certain proteins in the blood that promote blood clot formation.
At the same time, there is typically an increase in other proteins that are responsible for dissolving a clot. It is believed that this balance between clot formation and dissolution is important for preventing a heart attack. Caffeine is widely consumed by many people and can be used to improve athletic performance. However, caffeine may affect the heart and blood vessels in ways that are not healthy for some people.
This recent study conducted by scientists at Ball State University studied 48 young healthy men, evaluating the effect of caffeine on markers of blood clotting potential–with measures taken before and after exercise. This study showed that a single dose of caffeine increased blood clotting activity during exercise more than a placebo, but caffeine did not affect the proteins that dissolve blood clots. These results suggest caffeine may cause changes in the blood that promote clot formation and, thus, increase cardiovascular risk during exercise.