We need Vitamin C for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters. Vitamin C is also involved in protein metabolism. Collagen is an essential component of connective tissue, which plays a key role in wound healing. Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E). In addition to its biosynthetic and antioxidant functions, vitamin C plays a key role in immune function and improves the absorption of non-heme iron, the form of iron found in plant-based foods. Insufficient intake of vitamin C causes scurvy, which is characterised by fatigue or tiredness, widespread connective tissue weakness, and capillary fragility.
Oral vitamin C produces tissue and plasma concentrations that the body tightly controls. Approximately 70%-90% of vitamin C is absorbed with moderate intakes of 30-180 mg/day. However, at doses above 1 g/day, absorption drops to less than 50% and the ascorbic acid absorbed and not metabolised is excreted in the urine.
Exercise-Induced Bronchoconstriction (EIB) describes acute airway narrowing induced by vigorous exercise. This phenomenon is common among competitive athletes, even if they do not have asthma, and is particularly prevalent in endurance sports such as running, winter sports, and swimming. The stimulus for EIB seems to be the loss of water caused by increased ventilation. This leads to the release of mediators such as histamine, prostaglandins, and leukotrienes, all of which cause bronchoconstriction. Diagnosis is based on the maximum volume of air exhaled in one second (FEV1), which drops by more than 10% in the presence of bronchospasm. Several studies on EIB have shown that 0.5-2 g per day of vitamin C can reduce the drop in FEV1 by 50%.
In type 2 diabetes mellitus (2DM), vitamin C (0.5g, two times a day) together with metformin can promote the reduction of fasting blood glucose (FBS), post-meal blood glucose (PMBG), and glycosylated haemoglobin (HbA1c): double-blind study against placebo plus metformin conducted on 70 patients for 12 weeks.