The small study used the pure, enzymatically produced L-theanine dietary supplement Suntheanine manufactured by functional ingredients company Taiyo Kagaku Japan.
"Our clinical study strongly suggests that Suntheanine supplementation of young men can improve both the quality of sleep and the mental state of being refreshed on waking up," said the study's author, Dr Shuichiro Shirakawa, a professor at The National Center of Neurology and Psychiatry at the National Institute of Mental Health (NIMH) in Tokyo.
Rich in cancer-fighting antioxidants, green tea extracts are steadily being introduced into food and beverage products. The tea's active agent Epigallocatecin-3-gallate, is thought to aid a wide range of health conditions, notably lower cholesterol, prevent heart disease, fight bacteria and dental cavities, possibly aid weight loss and slow tumour growth in breast and liver cancers.
The recent study carried out by the NIMH is the first human study to show that L-theanine, an amino acid found in green tea, can enhance the quality of actual sleep experienced by young subjects. The research built on previous human studies that suggested Suntheanine supplementation could foster 'a relaxed state'.
The research was a blind crossover study involving 22 young men (12 daytime workers with an average age of 28 years, and 10 students with an average age of 26 years). After a three-day acclimatisation period, the men were given 200mg of L-theanine or a placebo, one hour before bedtime for six days. They were then crossed over to the other treatment group.
Sleep quality was assessed by interviews on waking up, self reported questionnaires and a wrist actigraph, to record bodily movements during sleep.
The researchers report that all subjects reported a significant absence of feeling exhausted and a reduced need for sleep when administered with the L-theanine, compared to the placebo.
Seven of the 10 students had improved sleep efficiency and these same subjects reported a superior mental state prior to sleep and a decreased occurrence of nightmares. Total sleeping time did not alter between the two groups.
"We are quite encouraged by the results of this clinical trial with Suntheanine, which marry well with our previous findings of promoting a relaxed state as measured by brain alpha waves," said Scott Smith, vice president of Taiyo International, the Japanese group's US subsidiary.
Research shows there could be a need for natural products to help combat insomnia - over 12 million sleeping pill prescriptions are issued each year in the UK alone, according to the Sleep Council.
Full findings of the research linking suntheanine to better sleep will be presented at the '17th Congress of the European Sleep Research Society', due to be held later this year in Prague, Czech Republic, October 5-9.