July 12, 2011 — New research shows that people who drink hot tea or coffee are about half as likely to have methicillin-resistant Staphylococcus aureus (MRSA) in their nasal passages as those who abstain, raising the prospect of a safe, inexpensive, and easily accessible way to decrease MRSA.
"In an effort to both prevent and treat MRSA, researchers have examined the antimicrobial effects of several commonly consumed plants and plant extracts," write the authors, led by Eric M. Matheson, MD, from the Department of Family Medicine, Medical University of South Carolina, Charleston. "What remains unclear is whether tea and coffee have systemic antimicrobial activity when consumed orally as beverages."
The study was published in the July/August issue of the Annals of Family Medicine.
The aim of the study was to evaluate the relationship between oral consumption of tea and coffee and MRSA nasal carriage in a nationally representative sample of Americans.
Researchers analyzed data from the 2003 to 2004 National Health and Nutrition Examination Survey (NHANES), a representative sample of the noninstitutionalized US population. The sample included 5555 people.
Survey Design
The NHANES uses a complex survey design that allows for population estimates. The sampling procedure consists of 4 stages, with the final stage involving individuals chosen to participate in NHANES from a list of those residing in selected households. These individuals are drawn at random from designated domains of age, sex, and race/ethnicity.
Researchers collected nasal cultures from all participants aged 1 year and older and assessed them for S aureus. However, because some variables were not available for very young residents, the analysis included only those aged 2 years and older.
The researchers evaluated consumption of hot tea, iced tea, and coffee, organizing responses into 2 categories: either (1) none or (2) less than 1 cup a month or more. Soft drink consumption was also classified into 2 categories: never to 2 to 3 times per month, or 1 to 6 times per week or more.
Potential Confounders
Investigators also looked at potential confounding variables previously associated with MRSA nasal carriage, including age, race, sex, poverty, health status, recent hospital stay, and antibiotic use.
Overall, 1.4% of the sample had MRSA nasal carriage. An estimated 88.6 million people (48.6% of the population) reported consuming hot tea in the past month. An estimated 110.7 million people (60.8%) reported consuming coffee.
Those who consumed hot tea had less than half the likelihood of having MRSA nasal carriage compared with those who did not consume hot tea (odds ratio, 0.47; 95% confidence interval, 0.31 - 0.70). After adjusting for confounders, hot tea drinkers still had a lower likelihood of MRSA nasal carriage.
The same association with MRSA was found with drinking coffee (odds ratio, 0.47; 95% confidence interval, 0.24 - 0.93), and the findings were similar for combined coffee and tea intake.
Iced Tea
The study did not find any significant relationship between iced tea drinking and risk for nasal MRSA carriage. "One possible explanation is that iced tea has lower levels than hot tea of polyphenolic compounds per unit volume, because many of the compounds in tea are more soluble at higher temperatures," the authors write.
There was also no significant relationship between the consumption of soda, which tends to contain caffeine, and MRSA nasal carriage. This suggests that caffeine is unlikely to be responsible for lower MRSA levels.
The mechanisms behind the seemingly protective effect of coffee and tea are not completely understood, but both these beverages appear to have antimicrobial properties. In the case of coffee, trigonelline, glyoxal, methylglyoxal, and diacetyl may have such an effect. For tea, attention has focused on tannic acid and catechins. Both beverages decrease iron absorption, which may be important because iron is critical for growth of S aureus, said the authors.
As not all research has linked nasal carriage of MRSA with the risk for systemic infection, the authors said the benefits of any treatment for MRSA nasal carriage should be carefully balanced against the risk.
View Cautiously
Asked to comment, Aaron E. Glatt, MD, president, chief executive officer, and professor of medicine (infectious diseases), St. Joseph Hospital, Bethpage, New York, and a spokesperson for the Infectious Diseases Society of America, said the research was interesting but should be viewed cautiously.
For one thing, the study only looked at people who did and did not drink coffee. "If I didn't take a sip of coffee, I'm in the first group; if I took a sip of coffee, I'm in the second group; and if I drank 35 cups of coffee a day, I'm still in the second group," said Dr. Glatt. "If you wanted to do this a bit more elegantly, you'd want to stratify it, to show, for example, that if you had 1 cup of coffee, there would no difference in MRSA, 3 cups of coffee, a reduction of 25%; 6 cups of coffee, a 50% reduction, and 20 cups of coffee, no MRSA."
There are other possible variables that may have reduced MRSA nasal carriage risk that were not looked at in the study, said Dr. Glatt. "I have no idea if it's the coffee that does this or some factor related to the coffee, but maybe people who drink coffee also wash their hands more frequently because they have access to a sink to pour their coffee out."
It is too early to recommend changes in hot tea and coffee drinking habits, added Dr. Glatt. "Information like this needs to be taken with a tremendous amount of thought. You don't want to suddenly recommend anything based on this, although it certainly merits further study."
