Coffee and Tea Preference and Addiction

David Letterman once stated that …”if it weren't for the coffee, I'd have no identifiable personality whatsoever.” In any given society caffeinated beverages can be found just about anywhere, and they are increasingly being consumed at an alarming rate. One study indicates that in North America between 80 and 90 percent of adults and children are habitually dependent upon caffeine. Researchers have questioned the probable causes of this dependency, and if routine caffeine usage could lead to potentially harmful effects?
In the study “The genetics of tea and coffee drinking and preference for source of caffeine in a large community sample of twins,” (Luciano, Kirk, Heath & Martin) researchers investigated the prospective genetic and environmental influences on tea and coffee consumption and preference. Studies have shown that long-term caffeine use is likely to increase potentially dangerous withdrawl symptoms including: Headaches, fatigue, depressed mood, irritability, and lack of motivation. Furthermore, the benefits that caffeine provides like increased energy, lucidity, and feeling of well-being are only evident in caffeine withdrawn individuals (those with 8 hours sleep), and not in those who have been pre-loaded with caffeine an hour earlier.
Previous twin-study research had revealed that there was some heritability factors associated with beverage preference and consumption. Additionally, prior findings stated a potential correlation could exist between caffeine consumption and alcohol / tobacco use due to genetic markers and drug dependency. Luciano, Kirk, Heath & Martin, believed these postulates to hold some water and each wished to expand on these ideas further. It should be noted that the researchers attempted to limit the environmental factors that could interfere with the final statistics.
The analysis was completed in a classic twin-study fashion, where data was polled from both parental and fraternal twins. A questionnaire was mailed to approximately 6,000 Australian twins over the course of two years. The survey asked the participants’ preference for coffee or tea, and average amount of daily consumption of their preferred caffeinated beverage. For any uninterruptable data, questionable answers, or inconsistencies the participants were telephoned to lower the miscalculation rate. Heritability factors were determined based on each set of twins’ responses to the survey. In other words, if one fraternal twin drinks 2 cups of coffee a day, what is the likelihood (heritability) that the other fraternal twin would drink 2 cups of coffee a day?
The final findings were rather inconclusive and stated many probable links to caffeine consumption and/or preference. For instance, the data depicted that coffee preference could be influenced by genetic taste perception. Since coffee has a bitter taste, one with strong taste buds could prefer to drink tea. This in turn could correlate with an increased “sweet tooth.” Again, this is based on the body wanting to satisfy that craving after ingesting a bitter tasting beverage.
The results also demonstrated that gender and age played significant roles in determining the final parallels. Older individuals and females consumed more tea, and had a lower coffee preference than younger participants and men. There were findings however, that backed more heritability in coffee consumption versus tea consumption. These stats could be due to higher caffeine content in coffee; therefore, a higher chance for addiction or dependency. The researchers noted that non-shared environmental facets could influence the participants’ answers (i.e. work place, family, location, etc). Lastly, the study concludes that tea and coffee consumption and preference are both affected by genes (caffeine dependency), and specific environment features (age, gender, etc).
This research did illustrate that there are some genetic dispositions that can affect individual dependency on a potential habit forming drug. I believe that a better developed, more recent study could be conducted to further supplement this idea. If researchers continue to find more connections with genetic factors, new studies can be developed to aid in alleviating conflicts with addiction, sleep patterns, and emotional abnormalities induced by dependency.
For future studies I believe that the results would have less variance if the researchers included energy drinks, soft drinks, chocolate and diet pills as part of their analysis. Additionally, decaffeinated products and artificial sweetners should be taken into account. Furthermore, the data was rather old, and generally the population consumes more coffee than tea, again this should be included in the reporting.

Reference
The genetics of tea and coffee drinking and preference for source of caffeine in a large community sample of Australian twins.
Authors:
Luciano, Michelle
Kirk, Katherine M.
Heath, Andrew C.
Martin, Nicholas G.
Source:
Addiction; Oct2005, Vol. 100 Issue 10, p1510-1517, 8p, 3 charts, 1 diagram