L-Theanine in green tea may modulate depression, anxiety and ADHD
The medical use of green tea is dated back to 5,000 years ago in China, when tea leaves were used to cure heart-related conditions, support digestive health and wound healing (Chen et al., 1994). Subsequently, to the development of traditional Chinese Medicine, tea drinking was recommended to healthy people for disease prevention between 1,100 and 200 BC (Yao and Chen, 1995).
One of the major compounds present in green tea is a free amino acid called L-Theanine. In human studies, synthetic L-Theanine supplementation was able to activate alpha brain waves, which indicate an alert, but relaxed state of mind (Cooper et al., 2005). Alpha waves also appear during meditation (Stern et al., 2001).
Animal studies found L-Theanine able to elevate brain concentrations of GABA, serotonin and dopamine, three very important neurotransmitters that regulate mood disorders like anxiety, depression and attention deficit hyperactivity disorder (ADHD) (Yokogoshi et al., 1998a; Terashima et al., 1999; Hyman, 2010, p108). ADHD symptoms are associated with low levels of dopamine, which may candidate L-Theanine as possible modulator. In children with ADHD, supplementation with 400mg of L-Theanine improved some aspects of sleep disturbance and increased sleep percentage (Lyon et al., 2011).
Another study found L-Theanine increased the function of a protein in the body called BDNF, which stimulates growth of brain cells in the memory centre called hippocampus (Takeda et al., 2011). Underactive BDNF is associated with depression (Yulug et al., 2010).
It is well known that elevated stress hormones, cortisol and adrenaline, are linked to depression and anxiety respectively (Jones and Quinn, 2005, p229). Some studies found L-Theanine able to reduce stress levels, while others found it to reduce anxiety and blood pressure (Kulkarni et al., 1998).
Although, supplementation with synthetic L-Theanine seems promising to better mood disorders, its dosages have not been accurately determined yet and other studies are needed.
I feel more confident in suggesting green tea consumption as a beverage in order to modulate brain function. In fact green tea, alongside L-Theanine, contains caffeine and the two work synergistically to improve attention tasks, reaction times and working memory (Kelly et al., 2008). It is relevant to say that other studies have linked caffeine to improved cognition and depression (Quinlan et al., 2000; Lucas et al., 2011). Studies made in Japan and Finland found more than four cups of green tea daily, containing an average of 80 to 160mg of L-Theanine, and around 150mg of caffeine, had antidepressant properties. Green tea is also rich in antioxidants, which can decrease chronic inflammation, another biomarker of degenerative brain conditions. By drinking green tea you will also stay hydrated, which may aid brain function.
So enjoy your cuppa with a little lemon juice and little honey if you wish.
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