Caffeine. Many of us look forward to a cup of coffee, tea, or cola to get us going in the morning or to lift our sagging midafternoon attention spans. Caffeine is one of the most comprehensively studied ingredients in the food supply and has a place on the Food and Drug Administration’s list of ingredients considered Generally Recognized as Safe (GRAS).
Although much is already known about the physiological effects of caffeine consumption, researchers continue to investigate caffeine’s health effects. As with most foods and ingredients, the key is moderation. Experts agree that most people can consume moderate amounts of caffeine (about 300 milligrams [mg] per day, which is equivalent to two to three 8-ounce cups of brewed coffee as generally prepared at home or five to six cups of brewed tea) without negative health effects. In light of concerns about rising rates of hypertension in the United States, recent research seeks to clarify the relationship between caffeine and blood pressure, especially in those population groups at risk for developing hypertension.
What Researchers Are Saying
The 1988 Surgeon General’s Report on Nutrition and Health drew an important distinction between the short- and long-term effects of caffeine consumption on blood pressure. For regular consumers, caffeine has no effect on blood pressure. People who do not consume caffeine regularly may experience a short-term increase in blood pressure after they consume caffeine. The effect is relatively small and temporary, and after about 2 hours blood pressure returns to the level that the individual had before he or she consumed caffeine.
Since publication of the 1988 Surgeon General’s Report, researchers have continued to gather data to understand whether the temporary effect of caffeine on blood pressure has any long-term health implications. The latest studies confirm much of what was already known, reaffirming caffeine’s safety in moderation and suggesting areas for further research.
A comprehensive review of the effects of caffeine on human health, conducted by Health Canada and published in 2003, determined that for healthy adults moderate daily caffeine intake is not associated with adverse effects, including cardiovascular problems such as hypertension. Finnish researchers reached similar conclusions in 1999, finding that long-term studies showed no relationship between caffeine consumption and blood pressure, although short-term studies detected caffeine sensitivity in some people. They highlighted the need for long-term clinical studies and epidemiologic research involving large numbers of participants to answer questions about caffeine consumption by hypertensive or hypertension-prone people.
Short-Term Studies Lead to More Research Questions
Short-term studies of specific populations elicit definitive information for that subgroup, but the results cannot necessarily be generalized to the population as a whole. As they are conducted under fairly specific conditions, these studies frequently generate suggestions for further investigation.
That is the case with a recent investigation of the effect of caffeinated beverages on blood pressure in a group of African-American and Caucasian adolescents. Researchers from the Medical College of Georgia reported that a small group of African-American teens in their study who consumed more than 100 mg of caffeine had higher blood pressure readings than Caucasian teens consuming the same amount. (A 12-ounce can of a caffeinated soft drink contains an average of 24 mg of caffeine.) The majority of teens in the study consumed 50 to 100 mg of caffeine per day and demonstrated no blood pressure effect, regardless of their ethnicity or race.
Several limitations in the study design prevented the investigators from drawing definitive conclusions. Although salt intake was controlled, the teens chose and consumed a variety of foods containing nutrients, such as potassium, magnesium, fiber, and fat, that may also influence blood pressure. The investigators noted that a teen’s caffeine consumption might not be an independent factor but, rather, a marker or indicator of other diet or lifestyle practices that together influence blood pressure. Thus, according to the authors, the take-home message of this one study is that more research is needed to separate out and clarify the multiple factors contributing to hypertension in teenagers.
Older adults are another population considered at risk for the development of high blood pressure, and several studies have examined the health effects of caffeine consumption in this group. Some research has focused on the idea that even the small, temporary, caffeine-related rise in blood pressure may have health significance for the older population over a period of time. Several short-term studies have yielded conflicting results that may be due to differences in age, individual differences in the response to caffeine, or simply differences in the ways in which the studies were conducted. Nevertheless, several researchers have suggested that older adults who are at risk for developing hypertension or who already have hypertension moderate their caffeine intake.
The Tolerance Question
Many studies report that regular consumers of caffeine develop a tolerance to it, and consequently, it does not have long-term effects on blood pressure. Researchers at the Veterans Affairs Medical Center in Oklahoma City challenged this conclusion in a study published in Hypertension earlier this year. Of 97 adults who regularly consumed caffeine, half showed small spikes in blood pressure shortly after taking capsules containing caffeine in amounts equivalent to about five cups of coffee over a 4-hour period. The authors say that the findings suggest the need for long-term studies on the effects of caffeine in people who are at risk for developing hypertension.
An editorial commenting on the study pointed out that the method of caffeine administration did not reflect the way in which people usually consume their caffeine-containing beverages. It stressed the lack of evidence linking caffeine consumption to increased blood pressure, even in people with hypertension. “In the absence of definitive scientific data, it would seem prudent to recommend moderation when it comes to the ingestion of caffeine-containing beverages such as coffee, tea, and cola drinks,” according to Dr. Martin G. Myers, University of Toronto. He noted that the regular consumption of caffeine can minimize any effects that it may have on blood pressure.
What Does It All Mean?
Hypertension is a complex condition with multiple causes and risk factors, and no study by itself tells the whole story. No doubt new research will add to our knowledge of caffeine’s health effects as scientists continue to take up the challenge of pinning down the dietary factors that have the most impact on hypertensive or hypertension-prone people. However, a vast body of scientific evidence from which we can draw a few conclusions already exists.
First, if you enjoy caffeinated beverages, whether it is a morning cup of coffee or tea or a soft drink during an afternoon break, you can certainly continue to do so. Experts generally agree that for most people, moderate caffeine consumption (300 mg per day) has no negative impact on blood pressure.
Second, this country’s medical information gatekeepers on whom we depend for authoritative advice and guidelines on health issues do not recommend caffeine reduction as a means of managing blood pressure. Although individual health care organizations define moderation slightly differently, the general recommendation is one to three cups of a caffeinated beverage per day. The American Heart Association states that “moderate coffee drinking (1-2 cups per day) doesn’t seem to be harmful.” The American Dietetic Association also advises that, “For most healthy adults, 200 to 300 milligrams of caffeine per day — about two to three cups of coffee — pose no physical problems.”
The National Institutes of Health’s Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure does not mention caffeine as a blood pressure risk factor in its newest report, issued in 2003. This group, which represents 46 professional, voluntary, and federal organizations, is charged with developing clinical guidelines for the prevention, detection, and treatment of high blood pressure.
For those people who are hypertensive or who are at risk for developing hypertension, advice concerning caffeine is best obtained from a health professional regarding scientifically supported means of managing the condition. Ongoing research may soon help to elucidate details specific to this group of people.
Experts do recommend a variety of lifestyle adjustments that have been found to be effective in lowering blood pressure. These include
- Weight reduction in individuals who are overweight or obese
- Adoption of the Dietary Approaches to Stop Hypertension (DASH) eating plan, which is rich in potassium and calcium
- Reduction of dietary sodium
- Increased amounts of physical activity
- Moderation of alcohol consumption
Information Resources on Hypertension and Blood Pressure
American Heart Association: http://www.americanheart.org
National Heart, Lung, and Blood Institute: http://www.nhlbi.nih.gov
International Food Information Council Foundation Publications:
