Caffeine is a natural stimulant found in the nuts, berries, and leaves of certain plants. Caffeine is most commonly consumed as coffee or tea products, and some have estimated that these beverages may be the most widely consumed foods in the world.
Because caffeine is so common in all human cultures, a great deal of research has been done to discover the health effects of caffeine. Relationships between caffeine and heart disease, as well as the caffeine-blood pressure link have been especially active fields of study.
What are stimulants?
Stimulants, by definition, increase the activity of the central nervous system, which is why they make you feel more awake, focused, and alert. However, this increased activity can also cause blood vessel constriction, which may increase blood pressure and alter the supply of blood to the heart. In fact, most of the dangerous effects of strong stimulants like cocaine and methamphetamine are a direct result of their activity on blood vessels and the heart.
Because caffeine is a stimulant, there is good reason to suspect that coffee and high blood pressure might be related. Caffeine, though, is a very mild stimulant, and has a short life span in the body. Caffeine is also a self-limiting stimulant, because it acts on the kidneys to increase the rate of its own excretion.
Caffeine, Blood Pressure, and the Heart
Evidence has repeatedly shown that consumption of caffeine does not increase the risk of high blood pressure, heart disease or heart attack. One very well-known study examined more than 85,000 women over a ten-year period and found that there was no increased risk of these diseases, even in women who drank more than six cups of coffee per day. The Joint National Committee on Hypertension has specifically stated that there is no evidence linking coffee/tea and high blood pressure.
While some recent studies have shown a weak link between caffeine and elevations in blood pressure, the results are complicated and only consider short-term effects.
For example, one widely quoted study found that blood pressure rose slightly in subjects almost immediately after consuming a caffeinated beverage, and that this blood pressure rise was more pronounced in people with pre-existing high blood pressure. However, these elevations were not very large and only lasted a short time. The study also showed that in about 15 percent of people with existing high blood pressure, drinking a caffeinated beverage actually caused a decrease in blood pressure.
Two important studies published in 2007 further supported the existing body of evidence by again demonstrating that:
- caffeine-induced blood pressure changes were small and short-lived
- caffeine does not contribute to disorders of the blood vessels associated with high blood pressure and cardiovascular disease
Coffee and tea may actually have many health benefits. While green tea was popular for several years as a healthy source of vitamins and antioxidants, newer research has shown that darker beverages like black tea and coffee may actually be better for you. These dark beverages are a rich source of compounds called polyphenols, which may protect against both heart disease and several types of cancer. Recent studies, for example, have consistently demonstrated a decreased risk of liver cancer in men who drink coffee.
Coffee and tea polyphenols have been shown to lower the level of activated platelets in the blood, which may help prevent blood clots that can lead to stroke. Polyphenols have also been shown to lower the body's concentration of C-reactive protein (CRP), an important factor in inflammation. Decreases in CRP have previously been shown to lower the risk of cardiovascular disease, heart attack, and certain types of kidney disease.
Though coffee and tea contain a lot of polyphenols, other types of polyphenols can be found in different foods. All polyphenols have been shown to have health benefits, but the most beneficial besides those in coffee and tea seem to be:
- Grape polyphenols
- Apple polyphenols
- Chocolate polyphenols (dark chocolate with more than 80 percent cocoa)