Dietary source of Vitamin C
Vitamin C is abundant in fresh fruits and vegetables. Most commonly known fruits are fruits with sour flavor such as orange, and kiwifruit. Vegetables like red pepper, green pepper, and broccoli also contain a large amount of Vitamin C. Vitamin C, however, is very prone to heat. If cooked over 80℃, half of Vitamin C was degraded in less than 20 minutes in red fruits (e.g. strawberry).  Although Vitamin C is easily attainable, vitamin C deficiency is the fourth leading nutrition deficiency in the United States according to CDC. 
Vitamin C Function
Vitamin C is a cofactor that is essential to enzymes that give collagen its structure and elasticity. Without Vitamin C, tissues lose their structural integrity and elastic tissue (e.g. gum) deteriorates.  Vitamin C also takes parts in creating enzymes that are important in regulating carnitine, catecholamine hormones, and amidated peptide hormones which are essential for proper body function.  There are evidences suggesting vitamin C provides neuroprotection for the central nervous system including the brain. Neurons have 10 times higher oxidative metabolism compared to nearby cells and Vitamin C, an antioxidant, protects neurons from getting damaged .
Vitamin C deficiency
The most well-known vitamin deficiency disease is scurvy also called sailors’ disease. It was a really common disease for sailors in the past who lacked vitamin C from fresh fruits and vegetables during long voyages. Scurvy is most characterized by swollen, bleeding gum, easy bruising, severe joint pain, leading to death from infection, and bleeding. When new collagen cannot be formed due to lack of Vitamin C, the most affected parts of our body are blood vessels. Capillaries that are just a thin layer of cells can rupture easily under blood pressure if collagen cannot hold it together. Collagen intense tissues such as gum and joint can no longer absorb shock and starts to degrade. 
Tiredness & Stress-related diseases
The common symptoms of lack of Vitamin C are tiredness and bad mood. Vitamin C is essential in producing catecholamine hormones including dopamine and norepinephrine. The cause of depression is best characterized by dysregulation of dopamine and norepinephrine and most anti-depressant medications targets these two systems ,. Regarding tiredness, researches show that oxidative stress is related to chronic fatigue. Vitamin C is one of the main sources of antioxidants in our body and its deficiency leads to higher oxidative stress.
- Reduce production of or provide protection against carcinogens (nitrosamines, benzanthrone) ,
- The most common cause of cancer is DNA mutation. Radicals are constantly produced in our body inevitably. These radicals can damage DNA, leading to carcinogenesis. Antioxidants like Vitamin C can protect cells from getting attacked by oxidative agents or carcinogens. 
- The current studies show very contradicting results on Vitamin C’s cancer prevention capability. Some studies report vastly improved statistics while some shows no difference between high dose and low dose. However, it might be due to subjects’ vitamin C level in plasma was already high before the experiment according to NIH.
- Improved quality of life for cancer patients going through cancer therapies. Vitamin C i.v. treatment showed a significant decrease in complaints from cancer and chemo/radiotherapy. According to a clinical trial with 125 breast cancer patients, the intensity score of nausea, fatigue, loss of appetite, depression, and sleep disorder, dizziness was reduced to nearly half compared to the group without Vitamin C treatment . This shows Vitamin C’s potential to improve the quality of life of cancer patients.
- Direct reduction of a tumor mass. Although it is pre-clinical data, a high dose of Vitamin C can reduce tumor volume significantly in rat models. In the experiment, Vitamin C treatment reduced tumor volume by about 50% in various types of cancer cells.  There several reports of Vitamin C’s efficacies in cancer treatments  but more clinical research is needed to be proved.
- Common cold
- Therapeutic use of Vitamin C after cold symptom arises is shown to be ineffective for the general population if taken after the symptoms show.
- For people involved in extreme physical activities or cold stress like athletes, Vitamin C supplements seem to have some beneficial effect but more study is needed to generalize it
- Regular Vitamin C supplementation over 200mg/day reduced common cold duration in adults by 8% and children by 14%. 
- Antidepressant property
- Some clinical studies show improvement in stress and depression scores compared to placebo . More clinical studies with tight control are needed to confirm
Min & Maximum dose
Min: Vitamin C is essential to human metabolism. The minimum recommended amount varies among different ages and gender from 40 to 100mg per day for males and 40 to 75mg for females. An adult male is recommended to take 100mg and an adult female to take 75mg per day. Smokers should take 35mg more per day to meet the dietary requirement according to NIH.
Max: There are no major side effects due to the overconsumption of Vitamin C. However, some people might experience diarrhea, nausea, and abdominal pain which are transient if the consumption level returns to normal.  Oral consumption does not increase blood Vitamin C levels that can be used in the body above 1000mg. Higher Vitamin C consumption that 1000mg will mostly not absorbed and even it does, it will be excreted through urine. 
- Verbeyst, L., Bogaerts, R., Van der Plancken, I. et al.Modelling of Vitamin C Degradation during Thermal and High-Pressure Treatments of Red Fruit. Food Bioprocess Technol6, 1015–1023 (2013).
2.US Centers for Disease Control and Prevention. Second National Report on Biochemical Indicators of Diet and Nutrition in the US Population 2012; National Center for Environmental Health: Atlanta, GA, USA, 2012.
- Jacob, R. A., & Sotoudeh, G. (2002). Vitamin C function and status in chronic disease. Nutrition in clinical care : an official publication of Tufts University, 5(2), 66–74.
- Carr, A. C., & Maggini, S. (2017). Vitamin C and Immune Function. Nutrients, 9(11), 1211. https://doi.org/10.3390/nu9111211
- May J. M. (2012). Vitamin C transport and its role in the central nervous system. Sub-cellular biochemistry, 56, 85–103. https://doi.org/10.1007/978-94-007-2199-9_6
- Dailly, E., Chenu, F., Renard, C. E., & Bourin, M. (2004). Dopamine, depression and antidepressants. Fundamental & clinical pharmacology, 18(6), 601–607. https://doi.org/10.1111/j.1472-8206.2004.00287.x
- Moret, C., & Briley, M. (2011). The importance of norepinephrine in depression. Neuropsychiatric disease and treatment, 7(Suppl 1), 9–13. https://doi.org/10.2147/NDT.S19619
- Hecht S. S. (1997). Approaches to cancer prevention based on an understanding of N-nitrosamine carcinogenesis. Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.), 216(2), 181–191. https://doi.org/10.3181/00379727-216-44168
- Dwivedi, N., Kumar, S., Ansari, K. M., Khanna, S. K., & Das, M. (2013). Skin tumorigenic potential of benzanthrone: prevention by ascorbic acid. Food and chemical toxicology: an international journal published for the British Industrial Biological Research Association, 59, 687–695. https://doi.org/10.1016/j.fct.2013.07.014
- Lutsenko, E. A., Cárcamo, J. M., & Golde, D. W. (2002). Vitamin C prevents DNA mutation induced by oxidative stress. The Journal of biological chemistry, 277(19), 16895–16899. https://doi.org/10.1074/jbc.M201151200
- Vollbracht, C., Schneider, B., Leendert, V., Weiss, G., Auerbach, L., & Beuth, J. (2011). Intravenous vitamin C administration improves quality of life in breast cancer patients during chemo-/radiotherapy and aftercare: results of a retrospective, multicentre, epidemiological cohort study in Germany. In vivo (Athens, Greece), 25(6), 983–990.
- Chen, Q., Espey, M. G., Sun, A. Y., Pooput, C., Kirk, K. L., Krishna, M. C., Khosh, D. B., Drisko, J., & Levine, M. (2008). Pharmacologic doses of ascorbate act as a prooxidant and decrease growth of aggressive tumor xenografts in mice. Proceedings of the National Academy of Sciences of the United States of America, 105(32), 11105–11109. https://doi.org/10.1073/pnas.0804226105
- Nauman, G., Gray, J. C., Parkinson, R., Levine, M., & Paller, C. J. (2018). Systematic Review of Intravenous Ascorbate in Cancer Clinical Trials. Antioxidants (Basel, Switzerland), 7(7), 89. https://doi.org/10.3390/antiox7070089
- Hemilä, H., & Chalker, E. (2013). Vitamin C for preventing and treating the common cold. The Cochrane database of systematic reviews, (1), CD000980. https://doi.org/10.1002/14651858.CD000980.pub4
- Moritz, B., Schmitz, A. E., Rodrigues, A., Dafre, A. L., & Cunha, M. P. (2020). The role of vitamin C in stress-related disorders. The Journal of nutritional biochemistry, 85, 108459. https://doi.org/10.1016/j.jnutbio.2020.108459
16. Levine, M., Conry-Cantilena, C., Wang, Y., Welch, R. W., Washko, P. W., Dhariwal, K. R., Park, J. B., Lazarev, A., Graumlich, J. F., King, J., & Cantilena, L. R. (1996). Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proceedings of the National Academy of Sciences of the United States of America, 93(8), 3704–3709. https://doi.org/10.1073/pnas.93.8.3704