There is a lot of information about it. Bloodletting improves insulin sensitivy in people with unnecessary iron.
Blood ferritin is a measure of stored iron. If ferritin is less than 70 ng/ml, the person has an iron deficiency. The normal range goes over 300 ng/ml, but those with a level of 140 ng/ml have higher triglycerides (insulin reduces triglycerides) than those with 70 ng/ml.
I haven’t had that checked, but my triglycerides are always perfect.