Topic Review: Vitamin C

$1,300,000,000 Global market for Vitamin-C supplements in 2019

148,796 million tonnes of Vitamin C exported from China to rest of world

75 milligrams recommended daily for adult women

10 milligrams of Vitamin C needed daily to prevent scurvy

30 milligrams of Vitamin C in one mango

130% Proportion of recommended daily Vitamin C intake from eating one  cup of strawberries

40% Proportion of recommended daily Vitamin C intake from one serving of kale

50% The amount of vitamin C you excrete as urine after taking 1000mg per day

 

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ORIGIN STORY

A curious sailor and the humble lemon

As far back as 1550 BC, reports of bleeding gums and poor skin health were usual in the general population. Hippocrates called this disease ileos ematitis describing symptoms: “the mouth feels bad; the gums are detached from the teeth; blood runs from the nostrils… ulcerations on the legs; some of these heal… skin is thin”.

Now known as scurvy, it wasn’t until the Age of sea-faring exploration in the 16th century that its impact became clear. In 1497, European explorer Vasco da Gama found most of his crew were afflicted with scurvy when arriving on the southeast coast of Africa. “Many of our men fell ill here, their feet and hands swelling, and their gums growing over their teeth so that they could not eat” he said. Up to 2 million sailors died of the disease.

In the 1700s, Scottish doctor James Lind of the British Royal Navy made a curious discovery that saved lives. In designing one of the first ever clinical trials, he found that crew who ate oranges or lemons on their long journeys were cured of scurvy. Lind’s discovery inspired his successors to persuade the British admiralty in the mid-1790s to end naval scurvy with prescribing juice of European lemons to all sailors.

By the 20th century, many were starting to look more deeply into why exactly lemons worked to cure scurvy.  By 1928, Vitamin C was isolated, and its importance in maintaining many biochemical processes for human health were confirmed.

Over the years, many have claimed higher doses of Vitamin C can cure or treat a range of conditions and diseases, most notably Nobel Laureate Linus Pauling in the 1970s. Today, many claim its benefits for preventing and treating Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) also known as COVID-19.

Let’s look more into those claims with Vitamin C experts.

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THE CONSENSUS

Does Vitamin C help with colds?

75% Likely via 4 experts

Read the full answers to this question here. On average, we get 2 bouts of the common cold each year. You’ve also probably heard that taking Vitamin C can help. Does it? We asked the experts and there are two separate questions important here: whether Vitamin C can prevent colds and whether they can be treated.

Prevention of Colds: “Research has indicated that vitamin C levels decrease in immune cells during the common cold, and supplementation may help improve the vitamin C status of these immune cells” says Dr Anitra Carr from the University of Otago. “A handful of studies have also indicated that supplementation with 200 mg/day of vitamin C can decrease the risk of getting the common cold by ~50% in people experiencing enhanced physical stress”.

Other experts confirm that Vitamin C appears to reduce the incidence of the common cold, but only in a small, specific population undergoing severe physical stress like marathon runners, skiers and high performance military personnel.. This effect is therefore not generalizable to most people as “vitamin C has not been shown to prevent colds in the general community” writes Dr Harri Hemila.

Duration of Colds: In terms of treating common colds, it seems by starting Vitamin C supplements at the onset of a common cold does not help but “there is very strong evidence that regular vitamin C supplementation of >200mg per day reduces common cold duration in adults on average by 8%, and in children by 14%” writes Dr Hemila. This effect only shows when maintaining adequate Vitamin C levels across 365 days of the year and most people get enough via their diet. “An optimal vitamin C status is thought to help avoid colds, and does shorten the duration and severity by a little. [However] most people achieve this through intake of sufficient fruit and vegetables, but many do not.” writes Professor Margreet Vissers from the University of Otago.

Why is Vitamin C important?

Infections cause depletion of vitamin C in the body and the benefit of vitamin C for colds seems to be explained by oxidative stress caused by the infection (Vitamin C is a powerful antioxidant).

However, Professor Jens Lykkesfeldt, an expert from the University of Copenhagen was uncertain about the efficacy of vitamin C in the treatment of colds, writing “Some studies have shown that there is a larger effect in people that are vitamin C efficient as would be expected. Unfortunately, very few studies have investigated vitamin C supplementation in people with poor vitamin C status. Therefore, we actually don’t know if vitamin C has the potential to alleviate common cold symptoms or reduce the frequency of disease, in particular in individuals that do not get enough vitamin C.” he writes.

How much to take?

If you are in good health, Dr Hemila says there is no need to take more than 1g/day. Despite the small potential benefits of Vitamin C for colds, “the practical significance is still an open question and further research is needed. We do not know what is the best dose and how much benefit we would get from the best dosages” he writes.

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THE CONSENSUS

Does Vitamin C boost immune function?

60% Uncertain via 5 experts

Read the full answers to this question here. Considerable experimental evidence suggests that vitamin C plays an important role in immune function writes Professor Jens Lykkesfeldt, “so getting too little vitamin C may negatively affect immune function”.

“We don’t necessarily know about all types of immune cells” writes Dr Anjana Rao from the La Jolla Institute of Immunology in California, “however, work from our lab has demonstrated clearly that Vitamin C increases the stability and hence the function of a subtype of T cells known as T regulatory cells, which protect the body from autoimmune diseases such as type I diabetes, systemic lupus erythematosus, rheumatoid arthritis and many others” she writes.

Despite these encouraging findings, there is “little clinical evidence available” that can be applied to the general population writes Professor Lykkesfeldt. “Some studies suggest that people with low vitamin C status (i.e. those not getting sufficient amounts though their normal diets, or those with extra needs such as smokers, pregnant women, sick individuals) may have increased risk increased risk of infections and perhaps this in fact due to inadequate vitamin C”. he writes.

But if you are healthy, maintain a good diet, do not smoke or have disease “it is highly questionable if taking more vitamin C will boost your immune function any further” he says.

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THE CONSENSUS

Are Vitamin C supplements necessary for maintaining good health?

80% Negative via 5 experts

Read the full answers to this question here. Vitamin C or ascorbic acid is a water soluble essential vitamin. Several foods contain vitamin C. Citrus fruits, cantaloupe, strawberries, papayas and mangoes are notable sources among fruits. Cabbage-type vegetables, dark green vegetables (like green peppers and broccoli), lettuce, tomatoes and even potatoes are some of the vegetables that provide vitamin C. Vitamin C is easily destroyed by heat and oxygen, hence eating whole raw fruits and some raw/steamed vegetables are recommended.

Adult men and women older than 19 yrs require 90 mg/day and 75 mg/day, respectively with smokers/passive smokers needing 35 mg/day more than their non-smoking counterparts. Consuming five varied servings of fruits and vegetables a day will provide an adequate amount of vitamin C, therefore, making supplementation unnecessary.

There are some individuals who might be at risk of vitamin C inadequacy. Deficiency symptoms include anemia, athrosclerotic plaques/pinpoint hemorrhages, bone fragility, poor wound healing, bleeding gums and loose teeth, muscle degeneration, rough skin and blotchy bruises.

All experts agreed that anyone can get enough vitamin C from a good diet to maintain good health. “Given that adults usually have on average 2 colds per year, lowering a cold duration by ~8% is quite small when considering vitamin C supplementation for 365 days. Nevertheless, in special conditions regular supplementation can be reasonable for the purpose of alleviating respiratory virus infections.For example, when someone frequently suffers from colds, regular vitamin C might be worth trying” writes Dr Harri Hemila.

Overall a good diet “should always be the first course of action” writes Professor Vissers. “This means eating fresh fruit and vegetables. Your body will not store vitamin C, so this needs to be a regular habit, not an occasional activity. Supplements are only recommended if you cannot access the food you need. Very sick people need more vitamin C daily, and a supplement may be recommended for this.”

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THE CONSENSUS

Is Vitamin C useful for type 2 diabetes?

67% affirmative via 6 experts

Read the full answers to this question here. Although the majority of the talk surrounding vitamin C is about colds and flu, others have pointed to benefits in combating lifestyle diseases like type 2 diabetes.

Most experts suggest vitamin C does have a use when it comes to the treatment of type 2 diabetes. Dr Cornelie Nienaber-Rousseau from North-West University cites recent findings that suggest glycemia improvements and decreased blood pressure after 4 months of supplementation with vitamin C vs a placebo. However, this research still needs to be replicated in larger groups with durations longer than 30 days or 4 months long she says.

Dr Walter Hsu from Iowa State University concurs writing, “Vitamin C is an antioxidant and we know that oxidative stress may be involved in insulin resistance, which is associated with type 2 diabetes. Therefore, vitamin C administration on a long-term basis might benefit patients with type 2 diabetes.”

Deakin University’s Dr Glenn Wadley also agrees. “In short, there is now evidence from well-designed but small (30-50 people with T2D) studies to demonstrate 1g/ day vitamin C lowers several blood glucose measures, such as fasting glucose, 24hr blood glucose levels and the post-meal blood glucose spike” he notes.

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Unlikely. Vitamin C or ascorbic acid is a water soluble essential vitamin. Several foods contain vitamin C. Citrus fruits, cantaloupe, strawberries, papayas and mangoes are notable sources among fruits. Cabbage-type vegetables, dark green vegetables (like green peppers and broccoli), lettuce, tomatoes and even potatoes are some of the vegetables that provide vitamin C. Vitamin C is easily destroyed by heat and oxygen, hence eating whole raw fruits and some raw/steamed vegetables are recommended. Adult men and women older than 19 yrs require 90 mg/day and 75 mg/day, respectively with smokers/passive smokers needing 35 mg/day more than their non-smoking counterparts. Consuming five varied servings of fruits and vegetables a day will provide an adequate amount of vitamin C, therefore, making supplementation unnecessary.

There are some individuals who might be at risk of vitamin C inadequacy. Deficiency symptoms include anemia, athrosclerotic plaques/pinpoint hemorrhages, bone fragility, poor wound healing, bleeding gums and loose teeth, muscle degeneration, rough skin and blotchy bruises. The deficiency disease of vitamin C is called scurvy and only appears when vitamin C intake is less than 1 mg/day (Hemila, 2017). At-risk individuals include: infants fed on evaporated or boiled cow’s milk, individuals with limited food variety (elderly, those who abuse alcohol or drugs, food insecure individuals) or those with medical conditions limiting vitamin C’s absorption.

Dietary vitamin C’s association with diseases has been researched for cancer, cardiovascular disease, age-related macular degeneration (AMD)/cataracts and the common cold among others. Dietary vitamin C intake is inversely associated with esophageal cancer (Bo et al., 2015) and lung cancer (Shareck et al., 2017), but not associated with ovarian cancer (Long et al., 2019) or pancreatic cancer (Hua et al., 2016) (as summarised by meta-analyses). Dietary vitamin C consumption has several benefits related to hearth health and those who are deficient have higher risk of mortality from cardiovascular disease (Moser and Chun, 2016). Ravindran and colleagues (2018) found that a genetic variant in a sodium-dependent vitamin C transporter gene that could proxy for lifetime ascorbate concentrations support a causal association of vitamin C with age-related cataracts. Vitamin C is unable to prevent or reduce the frequency of the common cold in the general population, but halved the number of colds in physically active individuals (Hemila, 2017). There is limited evidence for beneficial effect of vitamin C supplementation on markers of disease (Ashor et al., 2019). Granger and Eck argue that supplementation in populations with adequate vitamin C intake supplied through dietary sources will add no added benefit to impact diseases (Granger and Eck, 2018).

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TAKEAWAYS

• Good evidence that daily 200mg Vitamin C reduces the duration of the common cold by 8-14%
• Vitamin C supplementation is not needed for general health if maintaining a diet rich in fruits & vegetables
• Evidence suggests that daily Vitamin C supplementation lowers the risk of getting colds by ~50% in those undertaking severe physical stress (marathon runners, skiers and soldiers)
• No evidence Vitamin C can prevent or treat COVID-19
• There is some evidence that Vitamin C may help treat type-2 diabetes
• Safe levels of supplementation are 200-1000mg per day