The Diet Therapist


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Vitamin C


Vitamin C...Can it really boost immunity? 

Should you take a supplement?

Posted by The Diet Therapist, 18th February 2017

 Many people would struggle to describe the biochemical roles of riboflavin (Vitamin B2) or even Vitamin E. Vitamin C on the other hand, is not only familiar to most, but is ubiquitously linked with immunity. In fact, the immune-boosting potential of this nutrient been proclaimed for decades and supplements have become increasingly popular to protect against the usual onslaught of seasonal illnesses or help fight the common cold symptoms…but are Vitamin C’s immune superpowers really all they are hyped up to be?


Where did the idea that Vitamin C has “cold-combating” powers come from?

Vitamin C has been linked to immune support (initially via treatment of respiratory infections) since it was first isolated in the 1930s.  The work of Nobel Prize winning scientist Linus Pauling in his book “Vitamin C and the Common Cold” published in 1970, led to renewed scientific interest in this association, and consequently, a great deal of public debate over its biological and therapeutic potential for immune support.


By virtue of its potent anti-oxidant function, Vitamin C helps to protect cells from oxidative damage by reactive oxygen species (ROS), which are generated by immune cells to destroy pathogens.  It is also known to play an important role in the formation and function of leukocytes (white blood cells) and to support the production of cytokines, (cell-signalling molecules which help to regulate the immune system).  Though we know that Vitamin C (like most nutrients) plays a role in maintaining a healthy immune response, human studies looking at whether supplementation can enhance overall immunity are conflicting.  Clinical trials looking at the effect of continuous Vitamin C supplementation on the incidence, severity and duration of the “common cold,” have shown differing results. 


Studies examining doses of 0.2g/day or more of Vitamin C with healthy adults found that regular ingestion does not have a proven effect on “incidence”, i.e. it is probably not going to stop you getting that cold. On the other hand, researchers found that for those exposed to short periods of extreme physical stress (e.g. marathon runners, cross country skiers, and soldiers on heavy training exercises), it may offer some protective effects and lower the risk of illness.


Whether Vitamin C supplements can reduce the severity and duration of cold and flu symptoms after the onset of symptoms has also been hotly contested.  It is thought that Vitamin C may be beneficial, partly as a result of its anti-histamine effect, which is thought to help alleviate some of those nasty respiratory symptoms associated with the common cold and influenza.  However, trials examining this use “therapeutically” are limited with varying doses used, making it hard to draw any firm conclusions.


Is it worth taking a supplement?

Whilst Vitamin C supplementation is probably not the nutritional panacea some make it out to be – Pauling wasn’t entirely wrong either…If you’re training for a marathon or under a lot of stress in the office, it might be worth considering a good quality supplement, but bear in mind that many other factors influence immunity - small changes to your overall lifestyle, combined with improving the nutrient density of your diet are likely to have a greater cumulative impact. Vitamin C is just one of a host of nutrients which play important roles in the immune response, and mega-doses are unlikely to stop you getting sick, though supplements may have a minor effect on symptom relief.  


What is the best way to get Vitamin C?

Food, wholefood supplements & synthetic vitamins…

Unlike most animals who can synthesise Vitamin C endogenously, humans have lost this ability and must obtain it from their diet, with prolonged deficiency resulting in the disease “scurvy.” This was famously a problem for many of the world’s sailors causing a variety of symptoms including loose teeth, bleeding gums, and haemorrhages. Towards the end of the 15th century, scurvy was cited as the major cause of disability and mortality among sailors on long sea voyages, but it was not until 1753 that scurvy was recognised in the British medical community at large and related to dietary deficiency.  In 1747, the Scottish doctor James Lind carried out early experiments on naval ships finding citrus fruits to be effective in treating scurvy.  Sir (Walter) Norman Haworth, winner of the 1937 Nobel Prize in Chemistry, later deduced what we now recognise as the chemical structure of Vitamin C in 1933, but it would many more years and the work of Hungarian-born researcher Albert Szent-Gyorgyi (later recognised with a Nobel Prize in Physiology & Medicine), to isolate the metabolic mechanism that enables Vitamin C to be used within cells.


It is important to remember that the scientific evidence base for the association between Vitamin C and immunity is largely based on synthetic supplements featuring L-ascorbic acid, rather than whole foods, and this is so that the effect of a particular nutrient can be isolated.  A “synthetic” vitamin is one that been made in a lab, and within these there are different types; ones that are ‘bioidentical’ (i.e. the same in terms of molecular structure), as they occur in nature– as is the case with the vast majority of Vitamin C supplements – and those that are not, (as is sometimes the case with synthetic Vitamin E, for example). 


The chemical name for Vitamin C  -  “ascorbic acid” is derived from the disease it treats, a (meaning “no”), and scorbutus (the Latin for scurvy).  It primarily exists in 2 forms “L-ascorbic Acid,” and “D-ascorbic Acid.”  The former, L-ascorbic acid is the molecular and chemical form found in both natural and synthetic sources, and the latter D-ascorbic acid, (or D-Isoascorbic acid/Erythorbic acid), although chemically identical, its molecular arrangement is different. Though it has antioxidant activities, it only exerts about 1/20th of total “Vitamin C” activity.  This form cannot be used in supplements, but is licensed as a preservative anti-oxidant in products as “E315.” 


Research suggests that the bioavailability of Vitamin C itself (how well it is absorbed, metabolised and taken up by the cells and tissues) is unlikely to be affected by whether it is taken in purified supplement form, or received from whole foods.   However, in nature, biological constituents are coordinated.  When you eat kale, an orange, or a kiwifruit, there are various other nutrients and phytochemicals present in these foods.  Although studies show these do not affect absorption and bioavailability, some nutritional theorists have argued that nutrition science views about vitamin supplements are governed by a perspective that is too reductionist, i.e. “the whole is never equal to the sum of it’s parts.” 


Proponents of food synergy have hypothesised that the classic example of Vitamin C and scurvy demonstrates the primacy of the “cause and effect” concept in Nutrition Science.  This is the idea that the deficiency of a nutrient causes a specific disease - which can be explained (in biochemical and physiological terms) by the role played that nutrient.  Following this logic, that nutrient deficiency can be prevented (and often reversed), by consumption of that nutrient in an isolated “pure” form.  Most research focuses on studying single substances (macronutrients, micronutrients and other bioactive substances in food), rather than looking at foods-as-a-whole and patterns of synergy…a lot more difficult to research. The concept of “food synergy” or “thinking food first” states that the interrelations between different constituents in food are significant and should be acknowledged in research and policy.  This thinking stipulates that different vitamins and nutrients delivered by foods may have different effects from those formulated through technological processing, when taken directly from their natural biological environments. 


“Whole” vs “Fractionated…


Some authors have even argued that what we have recognised as Vitamin C since at least 1937, i.e. L-ascorbic acid does not reflect the true nature of Vitamin C, although this debate is not recognised in conventional medical research.  We know that in scurvy, the ascorbate ion (the fraction commonly found in ascorbic acid or in mineral salts such as sodium ascorbate or calcium ascorbate), is, at least at a biochemical level, what is missing in the body when scurvy causes death.  However, the total activity of Vitamin C biochemically cannot be reduced to ascorbic acid alone.  This is a complex, but critical element in the argument against fractionated synthetic supplements; within this distinction – the vitamin is the biochemical complex, but the vitamin activity refers to the actual biological and cellular changes that take place within the body when ascorbic acid acts in the presence of other “co-factors” such as flavonoids.  These theorists stress the functional interdependence of biologically related nutrient factors which have a range of effects when working together – greater than ascorbic acid alone.


Though there is very little scientific research in this area, it is in part, this thinking that has led to the emergence of Vitamin “complexes” and food-based supplements. It has long been acknowledged that vitamins and minerals do not exert their physiological effects in isolation, but together, and even at the level of absorption, some nutrients are affected (a well-quoted example of this is the impact of Vitamin D on calcium absorption) and some even compete with each other for absorption when taken together at certain doses (e.g. calcium and magnesium).  Many supplement companies now sell “complexes” which comprise doses of specific nutrients with their co-factors to support both absorption and use within the body.  For example, a vitamin B6 supplement complex which also contains magnesium, zinc, and vitamin B2 which are supportive co-factors in the utilisation of B6 in the body.  On top of this, vitamin deficiencies can cause mineral deficiencies, and imbalances in the ratio of one in relation to another, particularly with the trace metals, zinc and copper.


“Wholefood” and “food-based” supplements emerged in the market fairly recently, and these claim to be more “bioeffective” by offering vitamins and minerals with associated nutrients with which they occur in natural whole foods, as a “food complex.”  Food-state supplements are often lower potency in terms of milligrams, but made from natural food concentrates such as herb, fruit, vegetable and spice powders.  Other whole-food supplements may combine powders with specific synthetic nutrients, or create nutritionally rich complexes using food complexes, and/or yeast or bacteria.  With these, synthetic vitamins or minerals are fed into a food medium where they would naturally be found, (e.g. Vitamin C into citrus pulp) or to the yeast or bacteria which metabolise it.  The synthetic vitamins are molecularly combined into a food matrix in the same way they would be found naturally, but at a higher level, with co-factors intact.  Using this method reincorporates ascorbic acid into citrus pulp, but allows it to be absorbed in the same way it would be in an orange.  Whole-food and food-based supplements have not yet been extensively studied so the evidence-base for these is negligible.  However, considerable scientific literature exists on the concept of phytochemical and food synergy.  


Studies have shown that the biological mix of nutrients have more potent antioxidant effects than individual components alone.  In a study looking at the impact of nutrients in an apple on cell proliferation in colon and cancer cell lines in vitro, the small amount of Vitamin C contained in the apple did not inhibit the cancer cell line. Extracts of the apple flesh alone had some effect, but the greatest inhibition was seen with extracts of the apple together with skin.  The authors purport that the 100g of fresh apples with skin have a total antioxidant activity equivalent to 1,500mg of Vitamin C, although the actual amount of Vitamin C in the apples with peel is far less than this,  (approximately 5.7mg). 


Eating a varied diet including a range of nutrient-rich plant foods is more likely to have a support overall immune function by providing a range of compounds that act together, enhancing the effect of Vitamin C found naturally in foods and giving a range of other health benefits.  Foods that are high in Vitamin C (papaya, bell peppers, broccoli, watercress, kale, strawberries, cauliflower, melon, citrus fruit), also contain a multitude of other nutrients and phytochemicals as well as fibre, which help to maintain optimal health and wellbeing.  As Vitamin C is water-soluble and heat-sensitive, you can get maximum nutritional benefit from eating vegetables raw or lightly cooked (steamed or gently stir-fried). 


Though Vitamin C seems to have achieved a cult status amongst the general public, there are many other lifestyle and nutritional factors implicated in immune status and increased susceptibility to illness. Although a “magic bullet” in supplement form would be convenient, the best way to increase your immunity and ward off the seasonal cold and flu bugs is to make small, sustainable changes to your lifestyle and improve the overall nutrient-density of your diet.