parkinson's and theanine

Someone recently said they had great results for their husband from theanine. I did a medical research on it for PD and found 1 article (supporting it for PD). Almost every nutrient has some research for it in relation to PD, for or against, especially something as common as an amino acid like theanine. Even stranger is that it is probably 3rd after caffeine as the most important compound in green and black tea. That's strange because green and black tea are second to only nicotine and coffee in terms of evidence in preventing PD.