Drinking five cups of green tea per day may reduce the incidence of psychological distress by 20 per cent, says a new study from Japan.
In a study with 42,093 Japanese individuals 2,774 people, or 6.6 per cent of the study population, suffered from psychological stress, and green tea consumption was said to improve psychological well-being.
According to WHO estimates, more than 450 million people suffer from stress worldwide, with 17 per cent of Europeans stating that stress is the most important risk factor to health. The related costs of stress estimated at €20bn in Europe (WHO) and $200bn in the US (International Labor Office).
Researchers led by Atsushi Hozawa from the Tohoku University Graduate School of Medicine report their findings online in the American Journal of Clinical Nutrition.
Green tea and its extracts already have a positive reputation, with studies reporting they may offer protective effects against Alzheimer's and certain cancers, improve cardiovascular and oral health, and play a positive role in weight management.
Despite reports already stating that green tea or its constituents might reduce psychological stress, no large-scale study has evaluated the relationship between green tea consumption and psychological distress, said the researchers.
After adjusting their results for potential confounding factors, including age, sex, history of disease, BMI, alcohol consumption, cigarette smoking, diet, and other factors, a significant inverse association between green tea consumption and psychological distress was observed for people who drank at least five cups of green tea per day, compared to those who drank less than one cup per day.
Being an epidemiological study, the authors could not offer any evidence as to what the active constituents behind the apparent benefits could be. Further study is needed to elucidate the bioactives and mechanism of action.
The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).