Caffeine is arguably one of the world’s most popular drugs. Over 60 kinds of plants contain caffeine, which, depending on the species may be located principally in the leaves, seeds, nuts, beans, or fruit. The amount of caffeine in beverages, specifically coffee and tea, can vary widely depending on source, processing and preparation. Table 1 is a compilation from amounts that I found in a variety of books and journals. Each of these was derived from a number of sources ranging from governmental entities (such as the FDA), trade organizations (The National Coffee Association, The Gatorade Sports Science Institute, The National Soft Drink Organization, and The Consumer’s Union) and professional bodies. (American Medical Association, and the American Dietetic Association.) Unless you take caffeine in pill form, the amount in beverages is far from exact.

Caffeine and/or caffeine-containing beverages (specifically coffee) have been shown to be both linked to and have no association with, a variety of ailments including hypertension and heart disease. The evidence continues to be contradictory and, in a new study on caffeine and hypertension, even paradoxical.

Caffeine and Hypertension
Researchers looked at data from the Nurse’s Health Studies, Part I (NHS I, started in 1976 with over 120,000 RNs ages 30 to 55) and Part II (NHS II, started in 1989 with over 116,000 RNs ages 25 to 42).¹ The authors began by selecting all women in NHS I who were free of hypertension in 1990 (over 53,000) and all of the women in NHS II who were free of hypertension in 1991 (over 94,000). Records were analyzed for 12 years. In 2002 over 19,000 in NHS I had developed hypertension. In 2003 over 13,000 in NHS II were hypertensive. Dietary records from NHS I (1990, 1994, and 1998) and NHS II (1991, 1995, and 1999) were reviewed. The findings are in tables 2-4.

As you can see from Table 2, the results of this trial exhibit U-shaped curve with regard to caffeine and hypertension indicate there was a lower risk of hypertension at higher and lower intakes of caffeine with an increased risk in the middle. In Table 3, the risk of hypertension with coffee declined after one cup to a level where those who drank 6 or more cups daily had a 9 to 12% reduction compared to non-users. Tea confirmed the coffee results in NHI I but was contradictory in NHS II with risk paralleling consumption. (See Table 4).

Cola Surprise
Note that both sweetened and diet cola intake were the strongest predictors of increased risk for hypertension in both studies. (See Table 5 & 6). Confused? Well it may take genetics to sort this out. For example, a new study found an increased risk of caffeine related heart disease only in those who are genetically "slow" metabolizers. Those who are "rapid" caffeine metabolizers did not have a heart disease connection.² It turns out that people who carry the 1F allele on the liver enzyme cytochrome P4501A2 metabolize caffeine and have an increased risk of heart disease compared to those who carry the 1A allele. There could be some type of genetic influence on how certain people metabolize coke ingredients both individually and in combinations. In the meantime this research adds one more reason for both doctors and patients to reduce soft drink consumption. As far as coffee and tea, these findings indicate the need for further study.