Over the past several decades thousands of studies have probed the relationship between caffeine and health. Any possible links between caffeine and health risks, however, have proved elusive, suggesting that most people who enjoy moderate amounts of caffeine can continue to do so without cause for concern.
So why the continued confusion about caffeine? It may be the result of a handful of studies with equivocal results that have been interpreted in the media to have negative consequences of caffeine consumption. Three recent studies, however, add to the overwhelming body of evidence that moderate amounts of caffeine are not associated with health risks. In fact, caffeine may even have a protective effect on health when it comes to Parkinson's disease (PD).
A study reported in the Journal of the American Medical Association (May 2000) found that higher levels of coffee and caffeine intake is linked to a lower incidence of PD. Study participants were part of the Honolulu Heart Program cohort, a longitudinal study of 8006 men of Japanese ancestry, 45 to 68 years old, living on the island of Oahu in Hawaii. Researchers analyzed 30 years of follow-up data to study caffeine's effect on the incidence of PD. Dietary recalls assessed participants' levels of intakes of caffeine from coffee, tea, carbonated beverages, and other sources. Among the men followed during the 30 years, 102 developed PD. The risk of PD declined with increases in the amounts of caffeine consumed. Other nutrients contained in coffee, including niacin, and ingredients added to coffee (milk and sugar) did not alter the association between coffee and caffeine intake and the risk of PD.
The second study, published in the Journal of the American College of Nutrition (February 2000), examined the relationship between long-term caffeine intake and bone status among postmenopausal women. Researchers at the Pennsylvania State College of Medicine designed the study to minimize the effects of variables that can affect bone loss, including smoking, alcohol use, body weight, physical activity, and hormone replacement therapy (HRT).
Upon entry into the study, participants classified their usual caffeine intake as low, moderate, or high (equivalent to zero to two cups, three to four cups, or five or more cups of caffeinated coffee per day, respectively). Participants with various levels of physical activity were also recruited to control for the effects of exercise on bone density. Data were collected using 3-day diet records and bone measurements at two time points separated by 2 years; 138 women were seen at visit 1 and 92 women returned for visit 2 and remained in the sample.
Analysis of the results found no significant relationship between the participants' caffeine intake levels and changes in their bone density measurements from the first to the second study visit. When the results were analyzed on basis of high and low calcium intake levels, researchers observed no differences in bone loss by level of caffeine intake. The findings from this study add to the evidence that caffeine is not a risk factor for bone loss in women.
Finally, a third study (reported in more detail in a past issue of Food Insight) explored the belief that unpleasant "withdrawal" symptoms are common when regular caffeine consumption is abruptly stopped. The study, published in the Journal of Pharmacology (December 1999), was designed to determine the frequency with which symptoms of caffeine withdrawal occur and their clinical significance. The study involved a community-based telephone survey of 11,112 people, followed by a double-blind controlled study of 57 regular caffeine users with a self-reported history of caffeine- withdrawal symptoms. Throughout, participants were unaware of the study's focus on caffeine withdrawal.
In the phone survey, about 1 in 10 daily caffeine consumers reported symptoms of caffeine withdrawal if they stopped consuming caffeine abruptly.
Among the 18 subjects in the group from whom caffeine was suddenly withdrawn, only 6 subjects reported changes in mood and physical symptoms previously associated with caffeine withdrawal. The results of this study suggest that even among regular caffeine users who believe that they will experience caffeine withdrawal, the frequency and severity of symptoms are inconsistent and less than expected.
The widespread availability of caffeine-containing foods and beverages will likely fuel the continued scrutiny of caffeine. Current scientific research indicates it's safe to conclude that consumers can continue to enjoy their coffee, tea, and caffeinated soft drinks in moderation without worry.
