Welcome back to my series on the nutrients behind the diet.  I started this post series a little while ago, and you can find the links for the various posts in the series here: nutrients overview, carbohydrates, fats , proteins and Vitamin D. I also posted a summary of how our diet can affect our immune system recently, which you can find here.

First of all, What is Vitamin C?

Vitamin C is a micronutrient, meaning that we need it in small amounts. It is also known by a different name: L-ascorbic acid. Vitamin C is a water-soluble nutrient, meaning that we find it in the water-parts of foods rather than in fat.

Funny fact, but unlike many animals, humans cannot make vitamin C in our bodies, and so we must get it from our diet instead.

What does vitamin C do?

Antioxidant

Vitamin C is one of several nutrients that we call an antioxidant. What does this mean? Well it means that it helps to protect our cells from damage that is caused by free radicals. Free radicals are chemicals that are made when our bodies turn the food we eat into energy. However, we can also be exposed to free radicals from our environment, for example from air pollution, smoking and the UV rays from the sun. These free radicals can then cause something called oxidative stress, which may damage different proteins, fatty tissues and DNA in our bodies.

And Vitamin C does not just act like an antioxidant itself, protecting our cells. It has also been shown to make other antioxidants work better, such as vitamin E!

Helps us to produce proteins

We also need vitamin C to make a protein called collagen, which is needed to help us to build and repair tissues in our body.

Helps us to absorb iron from plants

Vitamin C also helps us to absorb iron from plant foods. This type of Iron is called non-haem iron. And it is usually less easy to absorb than iron found in animal foods. Having a food high in vitamin C around the same time that you eat a plant source of iron can increase how much of the iron you absorb! For example, have red peppers and tomatoes (Vit C) in a salad containing dark green leafy vegetables (Iron).

And it helps our immune system to work properly.

Vitamin C is needed in various stages of the immune system, from keeping our skin healthy, to helping our immune cells work properly.

Vitamin C and various conditions

Because Vitamin C acts as an antioxidant, it has been considered in research as a possible nutrient that may prevent or treat conditions which are related to oxidative stress. These conditions include cancer, cardiovascular disease, macular degeneration/cataracts and the common cold. Let’s review what some of the research has concluded about the role of vitamin C in these conditions so far:

Vitamin C and Cancer

We have evidence to suggest that diets that are higher in fruits and vegetables are linked to lower risk of various types of cancer. I had discussed this before in my post about the many benefits of fruits and veg on our health. Because these foods are higher in Vitamin C, and other anti-oxidants, researchers have wondered if taking even more vitamin C using supplements may help to reduce your cancer risk further.

Unfortunately at this time, the results from most clinical trials show that supplementation of vitamin C offers no benefit in protecting against cancer (1). Researchers think that this is because most people already get enough vitamin C from our diet, and we only see a very small increase in vitamin C levels in our bodies when we start taking supplements. Our bodies very carefully regulate how much vitamin C we store in our bodies, and so if we usually eat our recommended daily needs of vitamin C from diet, our bodies will not absorb as much of the supplements and will get rid of much of the extra vitamin C we absorb through our urine.

Vitamin C and Cardiovascular disease

Again, a diet high in fruit and veg is linked to a lower risk of developing heart disease and stroke. However, studies looking at the effect of supplementing a diet with vitamin C again found little further benefit from this increase in vitamin c (1, 2) This is again assuming that you get enough vitamin C from your diet alone – which most people do.

Vitamin C and age-related Macular Degeneration (AMD) and cataracts.

Current evidence does not show that taking vitamin C supplements will help reduce your risk of developing AMD or cataracts. However, a small amount of research does suggest that a specific supplement containing high doses of a variety of antioxidants may slow the progression of AMD for people who are at high risk of developing an advanced stage of AMD (1).

Vitamin C and the common cold

And ofcourse, there is a lot of hype at the moment about using vitamin C supplements when it comes to our immune system. While for the general population, regular vitamin C supplements are not shown to reduce your chances of getting a cold – one subgroup may see a benefit. People who do strenuous physical activity (now – this study looked at marathon runners, soldiers and skiers partaking in extreme physical exercise and cold environments) may see a possible reduction in their chances of catching a cold when they take a supplement of vitamin C regularly.

For the general population, they did find that taking vitamin C supplements before getting a cold may reduce the length of time that you have your cold, but only by 8%! This effect is slightly higher though for children, who see a 14% reduction in the length of time they have a cold. There may also be a slight reduction in how severe your symptoms get when you take vitamin C before you get your cold (3).

Vitamin C and gout or kidney stones

While this is not related to the antioxidant properties of vitamin C, there is a small amount of evidence to show that increasing your vitamin C intake may reduce your risk of developing gout. However, there is some evidence also to show that taking regular vitamin C supplements may increase your risk of developing kidney stones, especially if you have had them before .

So as you can see, with most conditions studied, there is very little benefit seen when people were taking supplements of vitamin C. And this is likely because very few people are actually vitamin C deficient in the first place! Let’s look now at how much vitamin C we need, and where we can get it from!

How much vitamin C do I need?

Irish guidelines recommend that adults need about 60mg of vitamin C a day (4). The US recommendations are slightly higher. They recommend that women need about 75mg and men about 90mg . And as we cannot store vitamin C in our bodies for very long, we do need to find a way to include it in our diet every day (1).

Interestingly, the US guidelines also suggest that you may need an additional 35mg a day if you are a smoker. Smokers are more subjected to free radicals and so may benefit from this additional vitamin C (1).

Then looking at safe upper limits. It tends to be recommended to stay below 2000mg (or 2g) of vitamin C daily.

Most people thankfully meet their requirements in Ireland. Irish men eat on average 114mg of vitamin C, and Irish women eat 141mg day (5). So this is almost double your recommended daily need for vitamin C!

What happens if I don’t eat enough vitamin C?

The typical condition you will find in people with vitamin C deficiency is known as Scurvy.  It was often seen in sailors up to the 18th century, who went on long voyages with very little fresh fruit or vegetables on board. Back then, they eventually found that bringing citrus fruits on board helped them to cure and prevent scurvy! While they didn’t know that it was “vitamin C” that was helping them back then, it was one of the first known experiments in managing nutritional deficiencies!

Typical signs of scurvy are poor wound healing, fragile skin, old wounds that may open again, you may see bleeding gums, teeth falling out and depression.

It can take up to a month of eating less than 10mg of vitamin C a day to develop symptoms of scurvy. Again remember that most people in Ireland eat over 100mg a day. And so thankfully scurvy is rare nowadays in developed countries. However, it can still be found very occasionally in people who eat very limited diets.

Groups at risk of low vitamin C intakes

So while true vitamin deficiency is rare, unfortunately some groups are still at risk of vitamin C intakes that are below the recommended daily allowances. This is not at deficiency level, but may be at a level below what we consider to be best for your health. The groups of people that may be at risk of not eating the optimal amounts of vitamin D are:

Smokers and passive smokers:

People who smoke are shown to have lower levels of vitamin C than non-smokers. Therefor in the UK, they are suggested to need an additional 35mg more than non-smokers. Unfortunately, even exposure to smoke through passive smoking has shown to have a vitamin C lowering effect. However there is currently not enough evidence to recommend a specific vitamin C intake for this subgroup.

People with limited food variety.

Fruits and veg are usually the best sources of vitamin C, however thankfully many other foods also have small amounts. Eating a variety of foods should mean that most people will meet their recommended intakes of vitamin C. However, people who eat very little variety, and have especially low intakes of fruits and vegetables, may still be at risk of inadequate vitamin C intakes. People who may be most at risk could include some elderly, people with very poor appetites, people who abuse alcohol or drugs, people with mental illness and at times children with very limited diets.

People with specific chronic diseases or malabsorption

Some people with medical conditions may be at risk of inadequate vitamin C levels. For example, intestinal malabsorption may reduce the absorption of vitamin C from the gut. Some conditions may increase the body’s need for vitamin C, for example cachexia or wound healing. We also see low vitamin C levels in some patients with end-stage kidney disease on haemodialysis, as the dialysis machine clears their blood of some of the vitamin C.

If you worry that you may fall into a group that is at risk of low vitamin C levels, it may be worth talking to a dietitian to see what you could do to make sure you get enough vitamin C through either diet or supplements.

Where can I find Vitamin C in my diet?

In Ireland, we get most of our vitamin C from fruit, then from vegetables and next from potatoes (5). Most fruits and veg are good sources of vitamin C. Foods especially high in Vitamin C include citrus fruits (such as oranges and lemons), red and green peppers and kiwi fruit. A mere half a cup full of red peppers contains more than your RDA of vitamin C already!

Some foods and beverages are also fortified with vitamin C. It will generally say on their label if there is vitamin C added.

Be aware that the vitamin C content of foods may be reduced by storing for a long period of time and by cooking. If you boil your vegetables, you will be losing some of their vitamin C to the water for example. It may be better to either eat your fruit and veg raw, or microwave or steam it.

So is there any benefit or harm to taking a vitamin C supplement?

Based on the evidence available, I would say that very few people would actually benefit from taking a vitamin C supplement. This is because again, the majority of people easily meet their daily recommended allowance for vitamin C already. And we saw that taking additional vitamin C on top of this showed only tiny increases in the amount of vitamin C stored in our bodies. Most of it will either not be absorbed or be peed out in our urine.

However, if you fall into the groups that I mentioned earlier as being at risk of low vitamin C intakes, so for example if you have a very limited diet, or have a condition that may affect how much vitamin C you absorb or need, then it may be worth talking to your dietitian or doctor about taking a supplement. Also, if you are an athlete, the evidence does suggest that you may see a reduction in how often you get a cold if you take a vitamin C supplement. It may be worth again discussing this with your sports dietitian if this is something you are interested to try.

Thankfully, Vitamin C supplements are generally considered safe for most people up to 1g per day. Be aware, if you do take more than 1g of vitamin C a day, some people may find that they have stomach pain, diarrhoea and flatulence. These symptoms will usually go away when you stop taking the supplements. They may also interact with some cancer treatments and potentially some heart medications. Its normally recommended to tell your doctor and pharmacist if you are taking any over the counter supplements, as they may be able to check if there are any potential interactions with your condition or medication. We also discussed earlier that there may be a slightly increased risk of developing kidney stones if you take vitamin C, especially if you have had a kidney stone in the past. Also, a very small study showed a potential risk of taking 2g of vitamin C a day for people with severe chronic pancreatitis, so we recommend to avoid vitamin C supplementation in this group also.

So to summarise.

Vitamin C is an important vitamin and antioxidant needed to maintain healthy tissues and a healthy immune system. We get vitamin C from a large variety of foods, mainly fruits, vegetables and potatoes, and in general, we easily meet our recommended daily needs for vitamin C from our diet alone. The research to date shows that for most people, there is little benefit to taking vitamin C supplements if you are already eating enough from your diet.

So really, as with most other nutrient supplements, I would suggest that vitamin C supplements are like the sprinkles on a cake. Get your diet right first, build a solid base, and then do you even still need the sprinkles?

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