The need for vitamin c is increased for which type of diseases

Mega doses of vitamin C have been widely used in the treatment and prevention of a large number of disorders like diabetes, atherosclerosis, common cold, cataracts, glaucoma, macular degeneration, stroke, heart diseases, cancer.

Vitamin C also known as ascorbic acid, is necessary for the growth, development and repair of all body tissues. It's involved in many body functions, including formation of collagen, absorption of iron, the proper functioning of the immune system, wound healing, and the maintenance of cartilage, bones, and teeth. 

The Recommended Dietary Allowance for adults 19 years and older is 90 mg daily for men and 75 mg for women. For pregnancy and lactation, the amount increases to 85 mg and 120 mg daily, respectively. Smoking can deplete vitamin C levels in the body, so an additional 35 mg beyond the RDA is suggested for smokers.

Severe deficiency of vitamin c is  called scurvy, causes bruising, gum and dental problems, dry hair and skin, and anemia. The diagnosis is based on symptoms and sometimes blood tests. Increasing consumption of fresh fruits and vegetables or taking vitamin C supplements by mouth usually corrects the deficiency.