Vitamin C, a.k.a. ascorbic acid is probably one of the best-known vitamins around.
It’s water-soluble meaning that it cannot be stored in the body like fat-soluble vitamins A, D, E & K can be. As such, the body requires a steady supply of vitamin C every day for optimal health.
Unlike most mammals and other animals, human beings cannot make their own vitamin C. Animals that can, simply convert glucose, derived from the digestion of foods with carbohydrates, into vitamin C in the liver and/or kidney.
Those animals that can produce vitamin C produce a boatload on a per kg of body weight basis.
For example, dogs produce about 2500 mg per day, whereas a 155 lb/70 kg goat about 13,000 mg per day; these amounts increase when the animals are stressed or are fighting infections.
Other animals, like apes, that don’t produce vitamin C eat several thousands worth of it every day because of their plant-based diets and yet the recommended intake of vitamin C for men is 90 mg and women 75 mg per day; an amount that will prevent an overt clinical deficiency of scurvy but is it enough for best health?
Interestingly, humans have all the same enzymes necessary to produce their own vitamin C from glucose but alas, the last enzyme is mutated and therefore defective.
The result? We don’t make any vitamin C on our own. Also interestingly, when people are sick or stressed, the activity of the other functioning vitamin C-producing enzymes increase in their activity suggestive that the body wants/is trying to produce more vitamin C in response to an infection like it does in vitamin C-producing animals.
There is a growing school of thought that is starting to see vitamin C deficiency as an inborn error in carbohydrate metabolism versus a classic vitamin deficiency.
Are the recommendations for vitamin C really evidenced-based?
The current recommendations have come under fire for their methodology and more.
Vitamin C ‘s pharmacokenetics were not taken into consideration when determining the RDA or Recommended Dietary Allowance. For those of whom are interested, the following two documents walk you through the science of vitamin C and the limitations with the current recommended intake.
Ascorbate – The Science of Vitamin C
Ridiculous Dietary Allowance – A Challenge to the RDA for Vitamin C
What is vitamin C?
Vitamin C is one of the 50 essential nutrients we need every day for optimal health. By bringing the works of Abram Hoffer and Albert Szent-Gyorgyi to the masses, Linus Pauling is credited as being responsible for the popularity of vitamin C supplements during the 1970s with his book Vitamin C and the Common Cold.
His other book on vitamin C How to Live Longer and Feel Better was equally popular. Pauling advocated high doses of vitamin C; between 3000 – 10,000 mg per day to treat everything from the common cold, heart disease, and cancer prevention.
Not surprisingly, he was mocked by the medical community and not taken seriously.
What is vitamin C’s function?
Vitamin C is needed for collagen production, one of the more important structural proteins of the skin, tendons, bone, teeth, cartilage and all other connective tissues.
Vitamin C is needed for proper neurotransmitter production, compounds that help to regulate mood, but vitamin C is best known for its role as a powerful antioxidant both in the blood and in tissues & cells throughout the body including the brain.
Oxidation is what happens to an apple core when it’s exposed to the air; it browns, or an iron nail exposed to water and air; it rusts. Oxidation of bodily structures like protein, fats, carbohydrates, and even our DNA, found in all tissues and organs, increases inflammation and the risk for chronic degenerative diseases.
Vitamin C helps to prevent this from happening by protecting us from free radicals and reactive oxygen species that are generated during normal metabolism, but also from the free radicals through exposure to toxins and pollutants.
These include first or second-hand smoke, exposure to, and the metabolism/breakdown of recreational and prescription drugs, alcohol, air pollution, inflammation from trans fats and diets high in sugar, as well as the toxins produced by viruses, bacteria and other pathogens that our immune is faced with every day.
Are Higher Amounts of Vitamin C Beneficial?
Despite what many critics say, who categorically dismiss the idea that intakes of vitamin C above the recommended 75-90 mg day, can offer any additional benefits, there is research out there for anyone who’s willing to do the work to find it.
Cardiovascular disease
One such study (pooled analysis) found that people with intakes of supplemental vitamin C at doses greater than 700 mg per day had reduced rates of coronary heart disease.
Mixed diets with several servings of fruits and vegetables can provide up to 350 mg making supplements a reasonable consideration to reach similar intakes of vitamin C that were found to be beneficial.
More recently, a study demonstrated that low vitamin C in the blood vessels [focal scurvy] has been shown to induce plaque build-up and Lp(a) to be deposited in arteries; the pivotal initiation of atherosclerosis.
Blood pressure
Looking at studies from 1966 – 2011, with an average, supplemented dose of 500 mg/day, vitamin C was found to reduce blood pressure in a clinically significant manner.
Vitamin C has also been shown to improve endothelial function, the ability of blood vessels to expand and relax improving blood flow, by increasing the gas that is responsible for this, nitric oxide; more nitric oxide = better blood pressure.
Colds
A report published in the Cochrane Database of Systematic Reviews looked at 72 placebo-controlled studies since 1966 excluding studies that used less than 200 mg per day.
They found that supplemental vitamin C reduced the risk for colds by 52% in those involved in extreme activities [marathon runners, skiers, soldiers and more].
Supplemental vitamin C offered an 8% reduction in the duration of symptoms in adults and a 14% reduction in children. Several other studies have shown that higher intakes of vitamin C can reduce both cold symptoms and duration.
Other studies found inconsistent results but this is likely due to how the vitamin C was taken; dosing and timing have a huge impact and influence outcomes.
Cancer
For years medical conventional wisdom stated that taking antioxidants during cancer treatment would interfere with treatment but this is falling by the wayside.
More and more research is finding that high dose vitamin C can improve outcomes, as well as, reduce the toxic effects of chemotherapy as with this study.
Three case reports on high dose IV vitamin C were also published in the Canadian Medical Association Journal among other publications.
Diabetes
Supplemental vitamin C has been shown to offer clinically meaningful benefits on blood glucose, lipids and serum insulin levels in those with diabetes at a dose of 1000 mg/day whereas 500 mg/day did not show any benefit.
Similar results have been found in a review of 44 clinical trials, 500 mg per day of vitamin improved endothelial function in those who stand to benefit from it the most, those with diabetes, those with existing atherosclerosis, and heart failure.
Bottom line
In a nutshell, there is evidence that consuming vitamin C in amounts more than what a healthy diet, with lots of fruits and vegetables, can provide, does have many health benefits.
To say there’s no research to support this is unfounded, and worse, biased.
It’s almost important to note that the amounts from supplements found to be beneficial are well under the Upper Level (UL) of 2000 mg/day.
The UL is the highest average daily nutrient intake level likely to pose no risk of adverse health effects; in this case loose stools.
Keep in mind that the 2000 mg cut-off is super conservative and is by definition a safe amount should someone choose to take higher amounts.
Anecdotally I’ve never had a client who had loose stools from large doses of vitamin C; doses that are above the UL, i.e. 4000-8000 mg/d provided it’s spread out over 2 to 4 doses.
Read about the superior absorption & bioavailability of Lypo-Spheric [liposomal] vitamin C in my post Take Your Vitamin C Supplement To The Next Level
Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, mental health. Follow me on Facebook, Instagram and Twitter.