How many cups of green tea do you need per day?
For regular tea, three to five cups per day appears to be the best-supported amount for heart and brain benefits, though the evidence is observational. For matcha supplements, no clear dose has been proven, and the small studies partly contradict one another.
Three to five cups of regular tea per day was linked to the lowest risk of stroke and dementia in a large British cohort of more than 365,000 people. That is an observational finding, not proof of cause and effect, but the association was robust across a follow-up of more than ten years.
For matcha (the powder made from ground green tea leaves), the doses used in studies are somewhat different. At 2 grams per day over one year, cognition in older adults with mild memory problems did not improve on the primary measure, but did improve on emotion recognition. At 3 grams per day over twelve weeks, cognition improved only in women, not in men. In short: a clear effective dose for cognition has not yet been established. Furthermore, several of these studies had (partial) industry funding, which puts the results in a slightly different light.
For muscle strength and muscle mass in men doing strength training, two small studies using 3 grams of matcha per day show a benefit. Here too, the groups were small, and the test products came from a commercial party. The findings are therefore preliminary.
One thing to be aware of: the polyphenols in tea inhibit the absorption of iron from food. For most people on a varied Western diet, this is barely relevant. If you are vegetarian, pregnant, or have anaemia, it is better to drink tea between meals rather than with them. Vitamin C consumed in the same meal helps restore iron absorption.
Based on one large cohort study (UK Biobank, n=365,682), two small matcha RCTs for cognition (n=61 and n=99), one small matcha RCT for muscle function, and one review on iron absorption. Several studies had industry funding (ITO EN, Nestlé Japan).