The current UK recommended daily intake of vitamin C is 40mg, but is this enough? Should we be taking supplements, or will they do more harm than good?
Recommended daily allowances (RDAs) are generally set to prevent vitamin deficiency diseases. Lack of vitamin C causes scurvy, which ultimately leads to death if adequate vitamin C intake is not restored. Symptoms of scurvy include slow wound and skin healing, frequent infections, bone and tooth weakness, tiredness and low mood, and damage to the cardiovascular system.
Vitamin C is now also widely recognised as being involved in a huge number of processes in the body and is considered an antioxidant nutrient. Vitamin C is involved in collagen and protein manufacture, so inadequate vitamin C intake is likely to accelerate the development of wrinkles.
As an antioxidant, vitamin C helps to protect the body from chronic diseases such as cancer, cataracts and heart disease and slows down the ageing process. This knowledge has lead researchers to question whether we should be revising the RDA to a much higher level.
As far back as 1999 the American Journal of Nutrition (1) published a review article which had analysed the results of recent trials and concluded that ‘ The totality of the reviewed data suggests that an intake of 90–100 mg vitamin C/d is required for optimum reduction of chronic disease risk in nonsmoking men and women.’ . In Canada the RDA reflects this: for adult males it is 90mg and females is 75mg, and higher for women who are pregnant or breast feeding.
It is widely acknowledged that smokers and the elderly will need more vitamin C than non-smoking adults.
Vitamin C supplements are widely available in doses up to 2000mg per day – this is a huge amount compared to the RDA. Should we be popping high dose vitamin C supplements daily?
The National Institute for Health states: ‘Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg/day. However, at doses above 1 g/day, absorption falls to less than 50% and the rest is excreted in the urine via the kidneys.’ (4)
High doses of vitamin C supplements cause diarrhoea and tummy pain, everyone’s threshold is different, so some people may get these effects with 500mg Vitamin C while others can tolerate 2000mg or more.
Vitamin C is not stored in large quantities in the body and it will pass quickly out in your urine. A study carried out on 22,000 men in Sweden over ten years suggested those who took vitamin C supplements seven days a week were at significantly greater risk of developing kidney stones (2). It is thought as excess vitamin C is excreted via the kidneys in the oxylate form it may build up and form calcium oxylate stones – kidney stones are extremely painful!
Antioxidant nutrients such as vitamin C, beta-carotene and vitamin E have great health benefits for the body, but ultimately when they are used up they become a source of free radical damage themselves unless they are recycled by another antioxidant nutrient. This is why it is important to take in a wide range of antioxidant vitamins through the diet and not mega- dose with just one vitamin.
As your body can only absorb limited amounts of vitamin C at a time, taking in regular doses of vitamin C via food throughout the day maybe better than taking high strength vitamin C supplements. (Vitamin C found naturally in foods does not cause any of the problems which may be associated with vitamin C supplements.)
Vitamin C is found in fruit and vegetables and these foods tend to be rich in other vitamins and antioxidants so whenever you eat them you are getting a range of antioxidants and vitamins alongside vitamin C, giving even more health benefits. For example, cantaloupe melon is a great source of both vitamin C and beta-carotene; avocado contains both vitamin E and vitamin C.
To ensure you take in good levels of vitamin C, eat some foods containing vitamin C at every meal or snack. Vitamin C is found in fruits and vegetables and is damaged or lost through cooking, so vitamin C rich foods are best eaten raw or lightly cooked. Frozen vegetables which have been frozen quickly after picking often have higher levels of vitamin C than vegetables which have been transported and stored for long periods of time before being sold.
Example of a diet rich in vitamin C: Eat a medium orange and a large kiwi fruit during the day as snacks, have a salad containing tomatoes and peppers with lunch and two steamed green vegetables at dinner. This would provide a vitamin C intake of around 200-300mg.
If you know you are not going to be five portions of fruit and vegetables a day for a few days because you are travelling, or you are unwell with an infection or going to be in an environment where you are smoking or passively smoking you may benefit from taking a 250mg -500mg vitamin C supplement once or twice daily. Ultimately, it is up to you to decide what you think is the best course of action to protect and maintain your health.
Below is a list of some foods and their vitamin C content. Vitamin C is not found in animal products or grains, only fruits and vegetables. For a more complete list see https://www.dietitians.ca/your-health/nutrition-a-z/vitamins/food-sources-of-vitamin-c.aspx
Vitamin C content of some foods:
1 large kiwi fruit 84mg
1 medium orange 60-80mg
Berries 125ml (1/2 cup) 14-17mg
Strawberries 125ml (1/2 cup) 52mg
Red peppers 125mg (1/2 cup) 101-144mg
Red cabbage, raw, 250ml (1 cup) 42mg
½ avocado 26mg
1 medium tomato 14mg
1 cup chopped watercress (34g) 14.6mg
1 medium carrot 3.6mg
Kale, cooked, 125ml (1/2 cup) 28mg
Steamed broccoli 125mg (1/2 cup) 54mg
Sweet potato, medium, baked with skin 22mg