Causes and needs
There is a large number of blood diseases ranging from red cell disorders like various anemias and bleeding disorders, to white blood cell diseases, like leucopenia, leukemias, lymphomas, Hodgkin disease, spleen ailments, thymic development disorders, and so on. And each one of these families of diseases may have several causes. So our bone marrow requires iron, vitamin B12, and folic acid, to produce normal red blood cells. If either of the vitamins is missing, abnormally large red blood cells are produced (megaloblastic anemia), and usually abnormal white cells and platelets as well.
The simple solution is to increase these vitamins in your diet. Unfortunately, this is often too simple. Remember, it is not what you eat that counts, but only what you absorb. And there may be a number of reasons for reduced absorption of these vitamins, including many anti-cancer drugs. The opposite type of anemia, small red blood cells, may be caused by a deficiency of vitamin C, when you have enough of it to avoid scurvy, but not enough to make normal red blood cells. This is a relatively rare type of anemia, because we usually have enough vitamin C in our diet. But these simple examples show that it is often not enough to know what nutrients to take. You must also know that you absorb enough for your needs.
Anemia in the elderly
To stay with anemias since it is impossible to discuss all blood disorders here, chronic disease linked to infection, inflammation, cancer, may also cause anemia, particularly so in the elderly. Such diseases tend to reduce the production of red blood cells by the bone marrow, and in the long run bring about anemia. This type of anemia usually develops gradually, has no symptoms, and is mild enough to pass unnoticed. When it develops, taking iron pills and vitamins is of no help. And there is no other specific treatment for this kind of anemia. Laboratory tests may show that chronic disease is the cause of the anemia, but they cannot confirm the diagnosis, never mind pinpoint the actual cause. Inevitably, your immune system may be weakened, with all the disadvantages and handicaps this kind of weakness implies.