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John Rennie
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This information is a mere Google away. The top result from that mere Google tells us that blood contains around 0.5g iron per litre of blood.

Another Google tells us an adult human contains around 5 litres of blood, though obviously it depends on the size of the person. And lastly there is no clear consensus on the amount of blood you can lose per day, but a 400ml blood donation can be made every 2 or 3 months. For several years I gave blood four times a year without any obvious consequences.

John Rennie
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