The researchers believe that green tea appears to be a relative safe option for treating anxiety and depression over prescribed anti-depressants and anti-anxiety medications which come with adverse effects. Researchers at Tohoku University Graduate School of Biomedical Engineering in Sendai conducted a study to assess the potential benefits of green tea consumption in alleviating psychological stress.
Details of the study
Dr. Kaijun Niu, lead author of the study and his colleagues examined 1,058 elderly Japanese individuals aged 70 years and above exhibiting mild and severe depressive symptoms.
Nearly 34 percent of the males and 39 percent of the women in the group demonstrated some symptoms of melancholy, while 20 percent of the men and 24 percent of the women showed signs of severe depression.
The patients were questioned about their daily intake of green tea. Out of all, 488 of the group confessed to drinking four or more cups of green tea a day, 284 said they consumed two to three cups daily while the rest reported having one or less cup daily.
Observations by the researchers
The investigators noted that the gloomy feelings were 44 per cent lower in participants who drank more than four cups of green tea per day as opposed to those who drank one or less.
The researchers found the same effect of the beverage on depressive symptoms even after taking into account factors such as socioeconomic status, age, sex, disease history, BMI, alcohol consumption, smoking, diet, and physical activity.
However, the scientists found that other tea varieties like oolong and black tea did not display similar anti-depression benefits.
According to researchers green tea contains L-theanine, an amino acid that promotes feelings of relaxation that has a soothing, calming effect on people who drink it.
Although L-theanine’s mechanism of action has not been fully elucidated, current research has focused on L-theanine’s effect on brain transmitters and brain waves.
Scientists believe that L-theanine supports the balance of various neurotransmitters such as serotonin and dopamine that play a key role in mood swings, in the brain. In a laboratory study, researchers found that L-theanine is able to cross the blood-brain barrier to support the activity of certain neurotransmitters in the brain.
In a recent study, the brain activity of 50 volunteers was measured after the oral administration of 50-200 mg of L-theanine. L-theanine promoted the generation of alpha-brain waves, considered to be an index of relaxation, in the volunteers. This study concluded that one way in which L-theanine promotes relaxation in humans is by increasing alpha brain waves.L-theanine has been shown to help the regulation of blood pressure. The same neurotransmitters that help us relax also regulate blood pressure in our bodies. When L-theanine is absorbed in our bodies, it results in slightly lowered blood pressure.
Laboratory studies have demonstrated that L-theanine affects both the nervous system and the cardiovascular system. Thus, L-theanine’s calming effect on our mental state is augmented by lowering blood pressure as well.
Despite the promising outcomes of the study, the scientists feel there is need for further research to draw a more tangible connection between green tea consumption and mental health.
The study was published in the December issue of the American Journal of Clinical Nutrition.