Are the cups of coffee your drink clamping down on your circulation? Caffeine is the most widely used stimulant and has complex effects on your blood vessels. Initial caffeine intake may promote vasodilation, but continued intake promotes vasoconstriction both directly and indirectly through the autonomic nervous system. Limiting your daily caffeine intake may help restore healthy blood flow throughout your body.
Caffeine Effects
Caffeine stimulates the nervous system by nonspecifically blocking the inhibitory effects of adenosine. Adenosine continually inhibits cells in the brain to maintain a stable level of signaling, rising to promote sleep. Caffeine also inhibits a class of enzyme called phosphodiesterases, preventing the inactivation of many signaling molecules. Mechanisms of additional effects vary in men and women. Caffeine in moderation can promote alertness, energy, improved mood and release of fatty acids from fat tissue.
Direct Effects on Blood Vessels
Initial doses of caffeine can actually promote vasodilation, or the expansion of blood vessels. Caffeine increases the expression of enzymes that produce nitric oxide and increases the concentration of cAMP, a signaling molecule normally inactivated by a phosphodiesterase. At the same time, caffeine also blocks the adenosine receptor in the cells of the blood vessel, causing vasoconstriction. These processes work against each other with the overall effect on blood vessel dilation or constriction varying between individuals.
Indirect Effects on Blood Vessels
In addition to promoting wakefulness in the brain, caffeine stimulates the sympathetic branch of the autonomic nervous system that is involved in the fight-or-flight response and stress. Among the many effects of activation of the sympathetic nervous system is vasoconstriction. Though the balance of the autonomic nervous system is complex, prolonged caffeine intake may lead to persistent vasoconstriction.
Healthy Intake
The average cup of coffee contains 70 to 120mg of caffeine. According to MayoClinic.com, a daily intake of 300 to 400mg of caffeine produces few side effects in most people. Higher intakes exceeding 500mg may cause nervousness, sleep disturbances, headaches, irregular heart beats, nausea and dehydration. The most reliable way to control your intake is to keep track and make sure that low-caffeine or caffeine-free alternatives are available.
References
- "International Journal of Vascular Medicine"; Caffeine's Vascular Mechanisms of Action; Echeverri et al.; 2010
- "Human Brain Mapping"; The effect of daily caffeine use on cerebral blood flow: How much caffeine can we tolerate?; Addicott et al.; 2009
- "Journal of Alzheimer's Disease"; Caffeine and Adenosine; Ribeiro and Sebastiao; 2010
- eMedicine; Neurologic Effects of Caffeine; Chawla and Suleman; 2008
- MayoClinic.com: Caffeine: How much is too much?
