Vitamin C (ascorbic acid) can be controversial. There are debates about how much is safe to supplement and a general lack of knowledge about how it is stored and used in the body.
Vitamin C in the body.
Vitamin C is used in the body in several ways:
- Formation of collagen, a connective tissue protein that is present throughout our body. Vitamin C contains 4 hydroxyl (HO) groups, which can add to collagen, changing its conformation and making it stronger. Collagen is involved in the function of blood vessels, tendons, ligaments and bones, as well as contributing to a firm skin tone. Without it we would shrivel up and our blood vessels would start to leak.
- Formation of norepinephrine, a neurotransmitter that affects our mood and our ability to get going. Norepinephrine levels are increased by some antidepressant medications.
- Synthesizing carnitine a molecule that transports fat to our mitochondria that improves our ability to burn fat. Lack of carnitine could contribute to fatigue, one of the first symptoms of the vitamin C deficiency disease scurvy.
- As an antioxidant that prevents our cells from being damaged by harmful free radicals. Its ability to regenerate other antioxidants such as vitamin E makes it particularly useful in this regard.
From the list above, you will probably conclude that it would be beneficial to have enough vitamin C in your body at all times.
Vitamin C storage.
Vitamin C is a water soluble vitamin, and I have heard people say that it is easily excreted from the body in the urine. This is not true. In fact, vitamin C is retained in our body by most of our organs and also in our blood plasma. Levels in blood plasma remain around 1.4 mg/dl. If they fall below this level, the kidneys reabsorb the vitamin C that passes through them. If it goes much above this, renal reabsorption decreases and more vitamin C is excreted. Our organs try to store vitamin C at levels much higher than those in blood plasma. For example, the adrenal glands, pituitary, thymus gland, and retina have more than 100 times the concentration of vitamin C than blood plasma.
What we see then is that our kidneys strictly control the amount of vitamin C that is present in the body based on our vitamin C status. Our vital organs need a fair amount of the stuff to be present, and if it is not, then our plasma levels drop and we begin to retain more vitamin C. However, we need to have enough of it. The question is how much is enough.
The recommended daily amount of vitamin C.
The RDA for vitamin C used to be 60mg and has now gone up to 90mg. Recommended daily doses are normally set at levels that are sufficient to prevent overt deficiency symptoms in 95% of the population. When you think about it, that means it must be well below what people should have. Why is that? Well, consider overt deficiency, which in the case of vitamin C is called scurvy. This overt deficiency disease occurs over a period of months. The RDA does not take into account long-term disease processes, such as heart disease, which are also thought to be affected by vitamin C status. Also, if you are just above the manifest deficiency threshold, you run the danger of falling under it if injured or ill. Any physical trauma tends to lower vitamin C levels quite markedly. Smoking also counts as physical trauma for these purposes, and it has been shown that even though most smokers also consume less vitamin C, they also have lower levels due to just smoking. It is also worth noting that frequent use of aspirin and the birth control pill decrease vitamin C levels.
It is also commonly thought that you may be overdosing on vitamin C, and symptoms such as kidney stones are frequently mentioned. The evidence for this is poor with many studies not showing an increased chance of kidney stones even with regular daily intakes of more than 1500mg. Some complementary medicine practitioners use even larger amounts of vitamin C intravenously, for example 28,000 mg every four days. The practice is quite widespread for the treatment of cancer, fatigue, and chronic infection. Research on the practice of intravenous megadosing of vitamin C seems to indicate that it is remarkably safe and that very few people experience negative side effects. Both my experience and research indicate that high levels of vitamin C supplements are safe for all but people with kidney failure. People with the common male inherited disorder, G6PD deficiency, may also be adversely affected, but serious complications are highly unlikely. With that being said, quite a few people will experience stomach upset such as nausea and diarrhea if they take large amounts of vitamin C by mouth. The best advice is to try it and limit it below the level at which any stomach upset occurs.
Why do we need vitamin C?
Vitamin C is synthesized by most animals. However, humans, chimpanzees, monkeys, bats, guinea pigs, and capybaras are among the few that do not. It is interesting to note that animals that synthesize vitamin C produce a lot of it. For example, goats that weigh the same as a lean human adult have been reported to produce 13 g of vitamin C per day. That is 140 times more than the current RDA. Similarly, other primates, which cannot produce their own vitamin C, consume at least 10 times more vitamin C in their diet than the current RDA. While some of the functions of vitamin C may be performed by uric acid in humans, it seems highly likely, given evolutionary evidence from other animals, that we should also be consuming much more than the current RDA.
Vitamin C is also associated with a reduced risk of some major diseases. Risk of heart disease it is likely to be reduced by 25% or more in those taking supplements of more than 400 mg daily. Risk of cancer it is also likely to be reduced, as vitamin C can help deprive a rapidly growing tumor of its oxygen supply. Taste is another condition where there is good evidence that supplemental vitamin C can help prevent or reduce symptoms.
So how much do I recommend?
Given the above evidence, I am convinced that vitamin C should be consumed in amounts significantly greater than the current RDA. My recommendation for most people is to eat a diet that is high in vitamin C. Depending on how much you eat, 300-600mg per day of fruits and vegetables would be a reasonable goal. For those with conditions that may benefit from supplemental amounts of vitamin C greater than 1 g (1,000 mg), it may well be worth a try.
Does vitamin C prevent colds?
Vitamin C has a mixed record in trials to demonstrate its ability to prevent colds or reduce their duration. However, many of the trials have tested amounts as small as 200 mg/day, which may be too small to be effective anyway. Testing with people subjected to harshness, such as people who exercise vigorously or who have been ill, seems to help prevent colds and reduce their duration and severity. For the common couch potato, it seems that prevention is not as effective, but that the severity and duration of colds can be reduced by regular supplementation. My own preference is to take a mix of vitamin c and zinc at the first sign of a cold.
Where can I get my C?
Vitamin C is mainly available from plant sources. The following list shows the amount of vitamin C available in 100 g of certain vitamin C-rich plants:
- Peppers 150-250mg
- parsley 130mg
- Kiwifruit 90mg
- Vegetables 30-90 mg (broccoli 90 mg, spinach 30 mg)
- Oranges 50mg
- Banana 9mg, Apple 6mg – so oranges have a lot more than banana and apples!
- Vitamin C is also available in animals, although not in as large an amount as many plants:
- Liver 12-36mg
- oysters 30mg
- Milk 2-4mg
- Meat <0.1mg, so not good for vitamin C
