It's a disorganized sentence containing two separate notions. One is that having fewer red cells can reduce the viscosity of blood so it doesn't clot as readily, which is good for sedentary people. The other is that bleeding will reduce the overall age of red cells and thus reduce the amount of unusable methemoglobin, containing oxidized iron. Iron (II) is in hemoglobin, Iron (III) is in methemoglobin.

I suffer from gout; there's a lot of theories about giving blood to help lower uric acid levels. Some people claim releif from symptoms after donating. In theory, it sounds plausable...

"Studies have shown that iron acts like a catalysis for the crystallization of uric acid. So if your iron serum levels are lower it will keep the uric acid in your blood longer to give your kidneys more time to remove it from your system."

https://www.reddit.com/r/gout/comments/70l8vp/reducing_uric_...

My old man actually _has_ to donate blood once a month due to excess iron from a condition.

Yup, I believe it’s called Hemochromatosis. I can’t find the source but I recall reading that donating blood also reduces cardiovascular risk.

Drinking water reduces blood viscosity too. Or so I've been told.