Vitamin C is a water-soluble vitamin found in citrus fruits, peppers, leafy green vegetables and tomatoes. It’s also known by its scientific name, ascorbic acid.
Vitamin C plays a role in collagen synthesis (the main structural protein in our skin and connective tissue), and helps the body absorb iron. It is also the most important antioxidant in human body fluid1 2, helping to protect cells by neutralising free radicals, unstable molecules which can damage DNA and cell structure.
What do we know about vitamin C and psoriasis?
The role of vitamin C in skin health is emphasised by the fact that vitamin C deficiency results in scurvy, skin lesions and poor wound healing.
Vitamin C also appears to play a role in regulating levels of inflammation in the body. Studies show higher levels of vitamin C in the blood are associated with lower levels of CRP, a marker of inflammation5, in both adolescents and adults.6 7
So how does this relate to psoriasis? Data is limited, but some research shows that people with psoriasis have lower levels of C vitamin in the skin than healthy controls8.
Higher levels of oxidative stress and impaired antioxidant status have also been linked to skin inflammation in psoriasis9 10, therefore it is possible that vitamin C may benefit psoriasis due to its antioxidant activity.
What does the science say?
The effects of vitamin C in psoriasis aren’t well understood because there is very little scientific evidence available. Anecdotal evidence (based on the personal experience of individuals) shows that some people find C vitamin supplementation makes their skin worse, while others report an improvement.
There are no studies of oral supplementation with C-vitamin in psoriasis. Studies of combined antioxidant supplementation have been inconclusive, some showing a positive effect with vitamin E, others no effect.11
Supplementation with 500 milligrams of vitamin C per day has been shown to effectively increase levels in the skin, but has not been shown to be effective in reducing sun damage12 when alone, although positive results are seen when combined with vitamin E.13
In one study of healthy, non-smoking adults14, vitamin C supplementation (1000 mg a day) for two months reduced CRP (a marker of inflammation) levels by 25% in those who had elevated levels at the start of the trial. No effect was found in those with normal levels.
In one Italian study15, higher dietary intakes of fresh fruits, carrots, tomatoes and fresh fruit were associated with a lower risk of psoriasis, but it is not clear whether the apparent protective effect was due to vitamin C, a combination of antioxidants, or other beneficial compounds found in fruits and vegetables.
It’s unlikely that excess intakes of vitamin C can be consumed through food alone. Long term supplementation with vitamin C appears safe16, although doses of more than 1000 milligrams (1 gram) a day aren’t recommended, as they can cause digestive distress, with symptoms such as cramps and diarrhoea.
With doses above 1 gram per day absorption of vitamin C also drops to less than 50 per cent, and the excess is excreted in the urine17.
How much do I need?
The daily recommended intake for vitamin C in the UK is 40 milligrams (mg) a day, which is easy to achieve through diet (an orange contains around 70 mg, and a medium pepper 150 mg) but it is difficult to say whether 40 mg is adequate enough for people with psoriasis, who tend to have higher levels of oxidative stress and lower antioxidant defences.
In the US, the Institute of Medicine recently increased the vitamin C recommendation to 90 mg per day for men and 75 mg for women18 based on evidence showing its importance as an antioxidant. However, these levels are also easy to meet with a healthy diet rich in fruit and vegetables.
- Vitamin C is an antioxidant vitamin which is concentrated in the skin which helps to protect against sun damage and ageing.
- Because of its role as an antioxidant, it may help to buffer the increase in oxidative stress seen in psoriasis.
- There is not enough evidence to say whether supplementation with vitamin C is helpful or not for people with psoriasis.
What the dietician says
We know that Vitamin C has powerful antioxidant activities, linked to protection against cancer and heart disease, but there’s not enough evidence to say how it can affect psoriasis.
People with psoriasis tend to have impaired antioxidant defences, so increasing intake of antioxidants through diet could theoretically be of benefit. Positively, fruit and vegetable intake has been correlated with higher levels of vitamin C and lower levels of inflammation. For this reason, it’s worth increasing intake of vitamin-C rich fruits and vegetables, as they also contain other nutrients such as fibre, which may benefit psoriasis.
It has been suggested that the current recommendations for vitamin C are too low for optimal health19, and that 90-100 mg per day is needed for disease prevention20, but even these levels are easily achievable through diet. The best sources of vitamin C are citrus fruits, tomatoes, potatoes, strawberries, bell peppers, broccoli, Brussels sprouts and kiwi fruit. Vitamin C is lost when cooking or storing for long periods, and studies show levels are higher in raw versus cooked vegetables.21 Of all cooking methods, steaming preserves the most vitamin C, so if you boil your vegetables, switching over could make a significant defence to your vitamin C status.22 23