Vitamins are crucial to the health of human beings. We get most of our vitamins from our diet with a couple of exceptions, vitamin B3 and vitamin D. Vitamin C, however, is a unique case, because during our evolution, right up to Lemurs, primates synthesized their own vitamin C. Most other animal species still do with some exceptions; some vertebrate fish, great apes, some bats, guinea pigs and humans no longer have that ability. So where did that ability go and what does it mean for the diet of humans?
The mutation in our genetic structure, for those interested, came from a gene that codes the enzyme responsible for catalyzing the last step of vitamin C biosynthesis, the L-gulono-γ-lactone oxidase (GLO) gene. This mutation may have occurred about 25 million years ago. The mutation of this gene was not considered critical to the survival of the species when it was lost since the primates of the time all had diets high in vitamin C. Even today, for instance, gorillas consume 20-30 mg/kg/day of vitamin C in their wild diets. If humans were to eat the same amount of vitamin C as a gorilla the average 180 lb. (81 kg) human would eat between 1600 and 2400 mg of vitamin C a day. 
Well known for its role in reducing the symptoms of colds, it is the strong antioxidant properties of vitamin C that help us fight illness. Vitamin C is used in the synthesis of amino acids such as carnitine, which is involved in the metabolism of lipids, tyrosine which is used to create proteins, and the synthesis of neurotransmitters. It is also crucial for the development of collagen, which is why a lack of vitamin C in our diet leads to the terrible and sometime fatal disease known as scurvy. Double Nobel Laureate, Linus Pauling once said that we are all living with a mild case of scurvy, as most humans do not get a sufficient amount of vitamin C in their diets, which he claimed was 3000mg a day, compared to the RDA recommended dietary allowance of 60 mg a day, or only 46 mg to avoid scurvy.
It is clear why we need to eat foods high in vitamin C, and if you aren’t eating like animals 25 million years ago you probably need a vitamin supplement. But more than that, vitamin C research has continued and new information is being revealed about vitamin C’s importance in achieving maximum healthspan.
If you read my article about NAC (livealonger.life/nac_miracle) you will understand the importance of glutathione. Vitamin C is known for maintaining the supply of glutathione, an important antioxidant. Research has shown that supplementing with at least 500 mg /day of vitamin C raises glutathione levels in red blood cells. Vitamin C levels above that didn’t seem to make a difference in the levels of glutathione. 
Staying alive longer often means overcoming the diseases that impact our ability to live longer according to the website, LifeExtension, "vitamin C can be helpful in preventing asthma, protecting against cancer, and supporting healthy blood sugar levels in diabetics."  More importantly, an important health goal is defeating the number one killer of Americans, heart disease. While there are many kinds of heart disease, atherosclerosis, hardening of the arteries, is caused by the buildup of plaque in our arteries, eventually clogging them. In 2002, scientists looked at the effects of vitamin C (ascorbic acid) on adhesion of large white blood cells to the walls of our arteries. It was already known that low levels of ascorbate in the blood put people at higher risk for adhesion of monocytes.
The result of this research showed that supplementing with as little as 250 mg/day of vitamin C after 6 weeks the level of white blood cell adhesion fell by 37%. This completely supports Pauling’s earlier suggestion that vitamin C is crucial for heart health. Another study at the University of Colorado at Boulder  showed that supplementing with 500 mg/day of vitamin C had the same effect on blood vessel tone as did those who took up a three-month regimen of brisk walking five to seven times a week. I do want to stress here that this study also showed that both the aerobic exercise as well as the vitamin C supplementation were substantially beneficial.
Linus Pauling felt strongly that vitamin C would end heart disease. He later modified his vitamin C alone idea to include the amino acid lysine. From his last interview, "I think we can get almost complete control of cardiovascular disease, heart attacks and strokes by the proper use of (vitamin C and lysine) ... even cure it." The doses of vitamin C he recommended for people with heart disease was 5000 mg a day and an equal amount of lysine. It’s important to spread your vitamin C intake out throughout the day as only small amounts of vitamin C, about 200 mg, can be absorbed at any one time. The rest is released in your urine. That’s one of the reasons most high-dose vitamin C supplements are slow-release.
Lastly, vitamin C is not known to make you lose weight but research has shown that it is linked to your body mass index (BMI). People in research studies have shown an overall lower BMI with high blood levels of vitamin C. Saddly, Vitamin C has not proven effective in the fight against cancer. Once touted as a cure by Pauling, all attempts to prove such have pretty much failed. Still, for heart health and immune system support vitamin C supplementation seems to be a no-brainer.
As always, live longer,
- Guy Drouin, et al., The Genetics of Vitamin C Loss in Vertebrate, Curr Genomics. 2011 Aug; 12(5): 371–378. doi: 10.2174/138920211796429736 PMCID: PMC3145266
- C S Johnston, C G Meyer, and J C Srilakshmi, Vitamin C elevates red blood cell glutathione in healthy adults., The American Journal of Clinical Nutrition 1993
- Woollard KJ, Loryman CJ, Meredith E, et al. Effects of oral vitamin C on monocyte: endothelial cell adhesion in healthy subjects. Biochem Biophys Res Commun. 2002 Jun 28;294(5):1161-8.