Would vitamin c helpful for thalassemia patient?

No: When anemic only a blood transfusion will help.

Yes, in small doses: Vitamin c can enhance iron absorption (something most with thalassemia don't need) but also enhance iron excretion if taken with desferal. There is evidence that vit c ; e are helpful in those who get transfusions- see http://www.Ncbi.Nlm.Nih.Gov/pubmed/16623048 however, too much c may be hazardous- see http://emedicine.Medscape.Com/article/206490-treatment 100 mg 2x/day is a safe dose.