Drinking Green Tea Linked to Less Psychological Distress

By Lori Bricker, MS, RD.

In a study just  published in the American Journal of Clinical Nutrition (see reference at bottom), Japanese researchers examined how green tea intake correlates to psychological distress.  Data were collected from a baseline survey of participants of the Ohsaki Cohort 2006 study, which included over 42,000 residents of Ohsaki City, Japan, aged 40 and over, on December 1, 2006.  Participants answered questions about green tea intake as well as coffee, black tea, oolong tea, alcohol, and other foods; tobacco use; time spent walking; history of disease; and height and weight.  The amount of social support the subjects had was determined by asking several questions, such as, “Do you have someone whom you can talk to when you are in trouble?”  The researchers also used a validated psychological distress scale in which subjects were asked questions about their mental state, such as, “Over the last month, how often have you felt hopeless?”

In evaluating the large amount of data this study produced, the researchers had to take into consideration many confounding factors that might affect mental stress apart from green tea intake.  For example, having a history of heart disease can increase mental stress, whereas having a good social support network may decrease it.  They were able to separate green tea’s effect from these kinds of confounding factors to determine that the effect of green tea was independent of 1) cardiovascular disease or risk factors for it, 2) intake of other foods or beverages, and 3) social support/activity.

Results:  The researchers concluded that green tea intake was inversely correlated with psychological distress, meaning that as green tea intake went up, psychological distress went down.  Specifically, the data showed that 8.4% of the subjects who drank the least green tea (<1 cup per day) had psychological distress, whereas only 5.1% of those drinking the most green tea (at least 5 cups per day) had psychological distress.  One cup of green tea was 100 mL, or about 3.4 oz., so this is a very reasonable intake.  They did point out, however, that they could not determine for certain whether green tea intake caused the lower psychological distress, or whether those without psychological distress were more likely to consume green tea.  But they suggested that because they were able to eliminate social support as a confounding factor, they think the green tea intake had a beneficial effect.  They recommend a different type of study be performed to better evaluate this claim.

It is interesting to note that in this study, black tea did not show the same correlation with less psychological distress.  Because another study  found a correlation between black tea intake and lower incidence of depression in the Finnish population (Eur J Epidemiol 2005;20:359-63), the researchers suggested that because the Japanese population drank so little black tea, the effect of green tea may have overshadowed any effect by black tea.

The most amazing thing about this study is the truly huge number of subjects.  This is often not possible, so I am thankful that tea-related information was gathered for such a large population.  The downside of a study like this is that dietary recall information is notoriously unreliable.  However, because of the enormous sample size, I hope we see a real trend here, even if the exact cup measures may be inaccurate.  If someone really does drink 5 or more cups of green tea a day, they know that they drink a lot of green tea, and certainly would not report that they drink <1 cup per day.

After I read this study, I immediately made a big pot of Genmaicha.

I really enjoy reading studies about the various health aspect of tea.  Please let me know if there is a particular topic you’d like to know more about.

Reference:  Green tea consumption is associated with lower psychological distress in a
general population: the Ohsaki Cohort 2006 Study
Atsushi Hozawa, Shinichi Kuriyama, Naoki Nakaya, Kaori Ohmori-Matsuda,
Masako Kakizaki, Toshimasa Sone, Masato Nagai, Yumi Sugawara, Akemi
Nitta, Yasutake Tomata, Kaijun Niu, and Ichiro Tsuji
Am. J. Clin. Nutr. published 30 September 2009,
10.3945/ajcn.2009.28214

http://www.ajcn.org/cgi/content/abstract/ajcn.2009.28214v1?ct

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