Thal majors are allowed only minimal levels of vitamin C daily, because C frees iron into the blood stream. Patients on desferal are told to take 200-250 mg C when they first start their desferal sessions, as this will create a more easily chelated free iron supply. However, at doses of 800 mg, some reduction in heart function was noted, so patients are told to limit their doses. I usually advise thal majors to get vitamin C through citrus snacks, so they're not taking high C foods with iron rich foods, to limit excess iron absorption from food. I think more research should be done in the area of vitamin C and chelators, to see if a higher dose of C could be handled with adjustments to the chelation. If this was possible, vitamin C could be used to speed up the rate of chelation by providing a supply of free iron. Since thal majors test almost universally deficient for C, it would be of great benefit if a way was found so thals could take more vitamin C.
Thal minors do not normally have to worry much about iron, so their vitamin C intake can be higher. Many minors have Hb levels in the normal range, so there should be no expectation of iron loading, as this is a reaction in the bone marrow to low Hb levels. If the Hb is normal or close to normal, there shouldn't be anything to worry about, but once it gets down to 10 or lower, bone marrow activity does increase and the gut absorbs more iron than needed in an attempt to raise the Hb. If Hb is typically below 10, there is more danger of iron loading. Minors in the 8-9 range would be most at risk for iron loading. Although C can cause more iron to be absorbed from food, the main thing to look at is how much iron is in the diet in general. That is far more relevant to iron load.