Outside the brain, caffeine can be a performance enhancer, boosting the strength of muscle contraction and offsetting some of the physiological and psychological effects of physical exertion. But, especially in the short term, it also has negative effects, which include raising blood pressure, making arteries stiffer, and increasing levels of homocysteine, insulin, and possibly cholesterol. Habitual use may cause some of these effects to wear off. For some conditions, though, coffee may have some benefit despite, rather than because of, caffeine.