The brain is very sensitive to nutrients and chemicals, that is why drug addicts becomes crazy as they damage their brains if not alter its functions partially/completely, temporarily/permanently. It is also the first one in the body to die due to lack of oxygen, so the oxygen plays a vital role in the brain functionality.
An anemic child is a dull child, they have the inability to learn if not to learn fast. They are the opposite of a bright child which learns fast and have no trouble of learning things that is taught to them. But the point is that if you are anemic your brain doesn't get much oxygen it needs to develop and learn as fast as it could in an optimized way.
I am a victim of anemia, at school I was wondering that why other students are so smart while I myself was struggling. This was when I am just starting to develop my kidney disease. So what more with a full-blown anemia where even the body's temperature regulation/endurance had been altered too.
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Anemia is one of the complications of being a dialysis patient and I thank God that it is not my problem anymore for the reasons I don't know. But I had suffered it especially in my College days that also made me stop my schooling plus the deterioration of my health. I am glad that I did though because I simply cannot cope anymore.
It means that one thing, in order to have your brain function in an optimized way it must get the best oxygenation from your blood. So a healthy blood is the one key for being smart, a foundation to be one of the best in a student's class or batch.
There are many ways to have a healthy blood and the fast way is to take some iron supplements with vitamin C so that the iron can get absorbed quickly. You will notice that after sometime you will sleep better, eat well better, think better, and get more sense of well-being.
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There are of course good food sources of iron like liver and red meats and green leafy vegetables and they must be combined in order for the iron content of both foods to get absorbed by the body and again with vitamin C your body will make them absorb iron more than not having vitamin C with them.