Green tea mainly comes from catechin - an antioxidant group that helps neutralize free radicals, protect blood vessel walls and maintain the elasticity of blood vessels. Catechin also promotes the body to create nitric oxide, which helps blood vessels dilate and supports blood pressure reduction.
You should drink green tea from morning until early afternoon. The reason is that tea contains caffeine, which can cause blood pressure to temporarily increase in some people. A 240ml cup of green tea contains about 29-73mg of caffeine. Although lower than coffee, the amount of caffeine is still significant if you drink many cups each day.
To limit the impact on sleep, you should stop drinking green tea at least 4-6 hours before going to bed. People sensitive to caffeine can stop drinking it immediately after lunch. If you want to drink it at the end of the day, you can choose decaffeineated green tea.
Drinking green tea too late can cause difficulty sleeping or waking up in the middle of the night. Prolonged sleep deprivation activates the sympathetic nervous system, causing heart to beat faster, blood vessels to constrict and making it difficult to control blood pressure.
Blood pressure usually drops during sleep. Interrupted sleep makes the body have less time in a state of low blood pressure, which in the long run can affect blood vessel health.
Drinking green tea extract after overnight fasting helps increase EGCG levels in the blood, suggesting that food can reduce the ability to absorb this compound.
Catechins can also bind to iron, so green tea should be taken at least one hour apart from iron-rich meals.
However, drinking on an empty stomach is not suitable for everyone. Some people may experience nausea, heartburn, or stomach discomfort.
