A green tea extract has shown some promise in initial clinical trials for treating chronic lymphocytic leukemia. Laboratory research determined that a compound in green tea extract, called EGCG, can kill chronic lymphocytic leukemia cells. A study of people with early-stage chronic lymphocytic leukemia found that EGCG in pill form reduced some signs of the disease. But green tea trials haven't been conclusive, and this subject requires more study before doctors can agree on the merits of this treatment.

Here's more info about the studies about EGCG and Vitamin D from 2010.
- Green Tea Extract Appears to Keep Cancer in Check in Majority of CLL Patients https://newsnetwork.mayoclinic.org/discussion/green-tea-extract-appears-to-keep-cancer-in-check-in-majority-of-cll-patients/
- Vitamin D insufficiency and prognosis in chronic lymphocytic leukemia https://www.researchgate.net/publication/47675948_Vitamin_D_insufficiency_and_prognosis_in_chronic_lymphocytic_leukemia

Thank you @boocat for sharing your story back to Mayo Clinic. I assume your CLL was diagnosed at an early stage. I'm glad that you are able to opt for active surveillance and see the hematologist every 6 months for a check in without needing treatment.