Vitamin C, also known as ascorbic acid, plays an important role in the growth, development, and repair of all body tissues. It's involved in many body functions, including the formation of collagen, absorption of iron, the immune system, wound healing, and the maintenance of cartilage, bones, and teeth. According to research from the Centers for Disease Control and Prevention (CDC), an estimated 7.1% of the U.S. population can be classified as being vitamin C deficient. (1) 

Vitamin C is a strong antioxidant and supports various cellular functions of the adaptive immune defense systems. (2, 3) Studies show that consuming more vitamin C can increase your blood antioxidant levels by up to 30%. This helps the body's natural defense to fight inflammation. (4) And Vitamin C has important contributions to skeletal health and helps in preventing osteoporosis. It is an essential cofactor for collagen formation which is the most abundant component of the extracellular bone matrix. (5) 

Vitamin C also helps improve the body's iron levels that affect growth. Vitamin C assists in converting iron that is poorly absorbed, such as plant-based sources of iron, into a form that is easier to absorb. (6) Research data carried out in Indonesia shows the fact that a decrease in iron intake can slow growth due to reduced iron transport capacity. In fact, simply consuming 100 mg of vitamin C may improve iron absorption by 67%. (7) 

It is well known that vitamin C plays an important role in skin health. Vitamin C is an excellent protection factor against UV irradiation. Skin fibroblasts have an absolute dependence on vitamin C for the synthesis of collagen, and for the regulation of the collagen - elastin balance in the dermis. Vitamin C supplementation of animals has shown improved collagen synthesis in vivo. (8) 

Vitamin C may help lower blood pressure for people both with and without high blood pressure which limits the risk of sustaining a heart disease. Taking a vitamin C supplement supports the relaxation of blood vessels that carry blood from the heart and helps to reduce the blood pressure levels. (9) Vitamin C supplements significantly reduce “bad” LDL cholesterol by approximately 7.9 mg/dl and blood triglycerides by 20.1 mg/dl. 

Vitamin C also protects memory and thinking. Vitamin C intakes from food or supplements can protect thinking and memory. (10) A lack of vitamin C can damage the nervous system. Studies have shown that dementia patients generally have lower vitamin C levels in the blood. (11) Vitamin C can also help to prevent colds, reduce cancer risk, and prevent eye diseases. 

References: 

1. Schleicher RL, Carroll MD, Ford ES, Lacher DA. Serum vitamin C and the prevalence of vitamin C deficiency in the United States: 2003-2004 National Health and Nutrition Examination Survey (NHANES). Am J Clin Nutr. 2009 Nov; 90 (5): 1252-63. 

2. Alessio HM, Goldfarb AH, Cao G. Exercise-induced oxidative stress before and after vitamin C supplementation. Int J Sport Nutr. 1997 Mar; 7 (1): 1-9. 

3. Anitra C. Carr, Silvia Maggini. Vitamin C and Immune Function Nutrients. 2017 Nov; 9 (11): 1211. 

4. Kim MK, Sasazuki S, Sasaki S, Okubo S, Hayashi M, Tsugane S. Effect of five-year supplementation of vitamin C on serum vitamin C concentration and consumption of vegetables and fruits in middle-aged Japanese: a randomized controlled trial. J Am Coll Nutr. 2003 Jun; 22 (3): 208-16. 

5. Sroga GE, Vashishth D. Effects of bone matrix proteins on fracture and fragility in osteoporosis. Curr Osteoporos Rep. 2012 Jun; 10 (2): 141-50. 

6. Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr. 2010 May; 91 (5): 1461S-1467S. 

7. Hallberg L, Hulthén L. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. Am J Clin Nutr. 2000 May; 71 (5): 1147-60. 

8. Juliet M. Pullar, Anitra C. Carr, Margreet C. M. Vissers The Roles of Vitamin C in Skin Health Nutrients. 2017 Aug; 9 (8): 866. 

9. Ettarh RR, Odigie IP, Adigun SA. Vitamin C lowers blood pressure and alters vascular responsiveness in salt-induced hypertension. Can J Physiol Pharmacol. 2002 Dec; 80 (12): 1199-202. 

10. Zandi PP, Anthony JC, Khachaturian AS, Stone SV, Gustafson D, Tschanz JT, Norton MC, Welsh-Bohmer KA, Breitner JC; Cache County Study Group. Reduced risk of Alzheimer disease in users of antioxidant vitamin supplements: the Cache County Study. Arch Neurol. 2004 Jan; 61 (1): 82-8. 

11. Charlton KE, Rabinowitz TL, Geffen LN, Dhansay MA. Lowered plasma vitamin C, but not vitamin E, concentrations in dementia patients. J Nutr Health Aging. 2004; 8 (2): 99-107.