How many cups of green tea do you need per day?
Two to three cups of green tea per day is the amount at which research shows the most health benefits, though cause and effect has not been proven. Let the tea cool a little before drinking; tea that is too hot increases the risk of oesophageal cancer.
Two to three cups of green tea per day is associated with the greatest reduction in risk of early death, cardiovascular disease, stroke and type 2 diabetes. Whether this is actually the cause has not been proven: it is based on people followed for years, without anyone telling them how much tea to drink.
For heart health, as few as two cups of unsweetened tea per day appears to be enough to get a sufficient amount of protective compounds (flavonoids). Higher numbers of cups are not consistently more beneficial in the studies.
For lowering blood pressure and managing weight, there is no clear-cut answer. Results vary widely due to differences in diet, physical activity and genetic background, so researchers cannot yet say which amount works best for those goals.
A practical safety point: let your tea cool down before you drink it. Tea hotter than around 55 to 60 degrees Celsius is associated with an increased risk of oesophageal and stomach cancer. Normal tea consumption is otherwise safe; liver problems and stomach complaints have only been reported with high doses of green tea as a concentrated supplement, not from drinking tea.
This answer is largely based on two large overviews that brought together dozens of earlier summaries of studies. The evidence for cardiovascular health is reasonably consistent, but because people were not randomly assigned to tea-drinking or non-tea-drinking groups, cause and effect has not been established. For blood pressure and weight, the researchers rated the quality of the evidence as low to very low, due to too many differences between the individual studies.
How many vegetables do you really need per day?
Five servings of vegetables and fruit per day offers the best protection, with non-starchy vegetables counting and juice and potatoes not. More than five servings adds nothing.
How many fruits and vegetables do I actually need per day?
Five portions of fruit and vegetables per day (two pieces of fruit, three serving-spoon scoops of vegetables) is the number with the strongest evidence base; eating more does not provide additional benefit, but most people do not even reach this minimum.
How much water do I really need to drink per day?
There is no magic number: for a healthy adult who is not very active, thirst is a reliable guide, with a total fluid intake of roughly 2 to 3 litres per day from all sources as a reference point. Drink more as soon as you exercise, when it is warm, or as you get older.
How much lithium do you need each day?
There is no official daily recommendation for lithium; scientists cite 1 mg per day as a cautious guideline, but evidence for benefits in healthy people is largely absent, so supplementation is not yet substantiated.
How much iron do you need per day?
For healthy adults without a deficiency, 1 to 2 mg of iron per day through food is sufficient. When a deficiency or anaemia is confirmed, requirements are much higher; discuss that with your doctor.
How much magnesium do you need per day?
Research suggests that your body reaches balance at around 165 mg per day, but official recommendations are higher and there is considerable individual variation. In any case, make sure you get enough magnesium-rich foods, as a large part of the population falls short.