The study, published in the American Journal of Clinical Nutrition, focused on 1,058 elderly Japanese individuals aged 70 years plus with the prevalence of mild and severe and severe depressive symptoms in the study population being 34 per cent and 20 per cent respectively, said the authors.
The authors maintain that only a few studies have investigated the relationship between green tea consumption and mental health, while there appears to be few studies assessing the relationship between green tea drinking and depressive symptoms.
According to the team led by Atsushi Hozawa, depression in the elderly is highly prevalent and can increase the risk of medical illnesses, worsen the outcome of other medical illnesses, and may increase mortality.
And the World Health Organization (WHO) forecasts that within 20 years more people will be affected by depression than any other health problem; it ranks depression as the leading cause of disability worldwide, with around 120 million people affected.
The findings show that the occurrence of depressive symptoms was 44 per cent lower for participants who drank more than four cups of green tea per day compared to those who drank less than one, after results were adjusted for factors such as age, sex, disease history, BMI, alcohol consumption, cigarette smoking, diet, and other factors.
The authors state, however, that their study is rather limited in scale and a larger population study that uses a standardized comprehensive structured diagnostic interview is required to confirm the effect of green tea consumption on depressive symptoms.
A previous study also led by the Hozawa found that drinking five cups of green tea per day may reduce the incidence of psychological distress by 20 per cent.
Green tea consumption was said to improve psychological well-being in a study population of 42,093 Japanese individuals of which 6.6 per cent suffered from psychological stress.
Industry is waking up to the potential of green tea outside its more well-known role as an antioxidant.
According to research from Unilever, green tea contains L-theanine, which is said to relax the brain.
Consumption of 50 mg of L-theanine (equivalent to two-three cups of tea) stimulates the alpha-brain waves associated with relaxation. By increasing the frequency of these brain waves, the beta-brain waves associated with tension are decreased, Frost and Sullivan said.
And consumer awareness of the benefits of green tea and green tea extracts continues to rise with growing numbers of studies, from 430 papers in 2000 to almost 1500 in 2003, reporting benefits of the main compounds, catechins.
Source: American Journal of Clinical Nutrition
Published online ahead of print: doi: 10.3945/ajcn.2009.28216
Title: Green tea consumption is associated with depressive symptoms in the elderly
Authors: K Niu, A Hozawa, S Kuriyama, S Ebihara, H Guo, N Nakaya, K Matsuda, H Takahashi, Y Masamune, M Asada, S Sasaki, H Arai, S Awata, R Nagatomi, and I Tsuji