Vitamin C use against the common cold was started by Linus Pauling research. But, this area is extremely controversial even to this day. A large amount of biased research muddies the topic. ref
Vitamin C has some family members that increase vitamin C activity as well as protect vitamin C against oxidation. Citrus Bioflavonoids, hesperidins, and rutin. They largely help with capillary fragility. Vitamin C in necessary for collagen production. Plus, flavonoids have unique functions other than the ones of vitamin C. ref
Check out the following two research study results to see why Vitamin C is controversial.
First Reference says in diabetic women, vitamin C increases Cardiovascular Disease.
Next Reference says high dose vitamin C reduces Cardiovascular Disease.
Which one is correct? Maybe both?
Here is a Reference four years later that supports the second reduced risk. The evidence appears to be building for a reduced risk except maybe in diabetics? Note that plasma vitamin C levels were obtained mostly from fruit and vegetable intake, although vitamin C level showed a greater reduction in risk of CVD than consumption of fruits and vegetables. One possible action is for reducing inflammatory marker C-Reactive Protein. ref Plus this Vitamin C research on increasing Glutathione levels impacting immune system. ref
FACT: Extreme Athletes taking vitamin C exhibit as much as a 50% reduction of common colds. Athletes after extreme exercise experience a lowered immunity and are more susceptible to cold viruses, especially during winter exposure. This vitamin C level of effect was not found in non-active people. article
VITAMIN C ON EXERCISE
Now it appears a full circle has occurred. Back to vitamin C and E having a negative effect on exercise induced positive insulin sensitivity. Remember that diabetes begins from reduced insulin sensitivity. Exercise helps prevent unless you take vitamins C and E when you exercise. reference Very Interesting! This aspect was covered before.
Bottom line goes back to the fact that the body needs a balance between anti-oxidants and pro-oxidation aspects. The body has adapted to use some pro-oxidants for beneficial functions before anti-oxidants step in and neutralize them. ref
NOTE: Here is another study showing high dose Vitamin C reduces the positive benefits of exercise on muscle endurance. The 1000 mg dose evidently was too much and destroyed some free radicals before the body could use them for positive functions.
VITAMIN C on IMMUNITY ref
Copy from above study reference conclusion: "Overall, vitamin C appears to exert a multitude of beneficial effects on cellular functions of both the innate and adaptive immune system. Although vitamin C is a potent antioxidant protecting the body against endogenous and exogenous oxidative challenges, it is likely that its action as a cofactor for numerous biosynthetic and gene regulatory enzymes plays a key role in its immune-modulating effects. Vitamin C stimulates neutrophil migration to the site of infection, enhances phagocytosis and oxidant generation, and microbial killing. At the same time, it protects host tissue from excessive damage by enhancing neutrophil apoptosis and clearance by macrophages, and decreasing neutrophil necrosis and NETosis. Thus, it is apparent that vitamin C is necessary for the immune system to mount and sustain an adequate response against pathogens, whilst avoiding excessive damage to the host." Another ref
VITAMIN C on GLYCATION
Vitamin C and it's effects on the glycation process ref ref need to be added into this discussion. Does Vitamin C act as a pro-oxidant in diabetics as the first reference above suggests? In this capacity it would increase glycation and speed artery disease, an effect observed in diabetes. There could be other factors that determine which way vitamin C goes on this issue. ref <What is Alc ref Is it possible that since vitamin C is made from glucose in most mammals, it is still close to the same molecule and reacts with proteins just like glucose? OR, it might just be that higher vitamin C levels are associated with higher glucose levels, an associated factor for diabetes.
This last ref is an in-depth look at the research with analytical intent. The vast majority of research shows vitamin C acts an anti-oxidant. The few reports of C as a pro-oxidant are in test tube studies with the addition of an ion metal such as copper acting to oxidize LDL cholesterol. This unique set of circumstances needed for this probably almost never occurs in the body. One has to say almost or rarely since some flukes have been found to happen, like vitamin E changing from an anti-oxidant into a pro-oxidant from the effects of an element in cigarette smoke leading to increased lung cancer.
For a good reference on vitamin C with research summaries. Note this is a Government site and is very cautious about some of the newly discovered vitamin C actions. All things technologically Vitamin C here.
Vitamin C, Flavonoids, and Cancers (this will need another article)
This topic is still undergoing research. Here are some of the facts. Vitamin C has two transporters, SVCT1 and SVCT2. the transporter vitamin C connects with determines where in the body it will go. ref The next reference talks about these two vitamin C transporters on skin sun damage protection. ref
Natural versus Synthetic Vitamin C
This topic generates quite a bit of controversy. First, here is what is known. Natural vitamin C made in an orange has the same elements as ascorbic acid processed in the lab usually from corn sugar. But, there are two different isomers that may develop, L-ascorbic and D-ascorbic. An isomer is a slightly different arrangement of the same elements. in the orange, vitamin C is all in the L-form. Synthetic Vitamin C is also produced in the L-ascorbic form. The D-form can be made in the Lab and is used in foods as a preservative. It is not active in the body for vitamin C activity except as an antioxidant.
Some animal studies show differences between the two, but so far, human studies have not found the differences observed in those animal studies. It might be that the differences are difficult to observe or that in the body, the differences are not significant. Because most animals make their own vitamin C, only a few are available for vitamin C studies. This area needs more research. But, what is known, is that vitamin C benefits from the inclusion of bioflavonoids. Bioflavonoid exhibit a protective effect on vitamin C as well as have benefits of their own.
One small point of difference between natural vitamin C with bioflavonoids versus synthetic vitamin C concerns the time to reach max peak, the length of time at that level, or the area ounder the curve as science measures, and the speed of elimination by urine. Synthetic vitamin C speeds to a max first and then reduces faster than natural vitamin C. This could be of some significance, but is mostly observed at 500 mg or higher amounts of vitamin C.
This is an area of continuing research.
DOSAGES on EXCRETION AMOUNTS
At 100 mg per day, there is no vitamin C found in urine. Over 100 mg there is 25%. At 200 mg, the percentage doubles to 50%. Plus, at 200 to 250 mg. vitamin C reaches a peak of blood levels that is not increased until dosages reach 2,500 mg. This does not necessarily mean the extra is not working before it is excreted. At one gram per day there is a peak reached for tissue, plasma and blood levels. But over 250 mg, urine excretion rapidly increases and absorption decreases. Extra vitamin C could still increase somewhat in other tissues and organs. Mostly a factor of longer time in body not higher levels ref
At 3 grams of vitamin C per day, the body reaches the top excretion percentage amount. There is now unmetabolized vitamin C found in urine. Plus, there is also the development of an enzyme system to destroy the extra vitamin C in the body. ref A rebound effect must be at play if one abruptly stops taking large amounts. ref This enzyme is still produced for awhile which lowers the dietary vitamin C levels below pre-study amounts. This rebound negative action lasts for about 10-12 days.
The above details explain why the new vitamin criteria dosage for vitamin C is just 250 mg. Another factor is revealed by this study. ref It shows that higher vitamin C (857-5000 mg/day) increases the thickness of carotid arteries faster than the increase from just food sources of vitamin C, at amounts much lower than the 857 mg.
Team RightWay