Podcast: Vitamin C supplementation to prevent cardiovascular disease

Many people take vitamin C with a view to preventing, treating or helping with various conditions and there are Cochrane Reviews of its effects in diabetes, pregnancy and for some lung conditions. In March 2017, these were added to with a review of whether vitamin C can prevent cardiovascular disease and we asked the first author, Lena Al-Khudairy from Warwick Medical School in the UK to tell us more.

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John: Hello, I'm John Hilton, editor of the Cochrane Editorial unit. Many people take vitamin C with a view to preventing, treating or helping with various conditions and there are Cochrane Reviews of its effects in diabetes, pregnancy and for some lung conditions. In March 2017, these were added to with a review of whether vitamin C can prevent cardiovascular disease and we asked the first author, Lena Al-Khudairy from Warwick Medical School in the UK to tell us more.

Lena: Vitamin C is an essential micronutrient, with powerful antioxidant mechanisms and potential health benefits for a large number of conditions. We were interested in whether it has an effect on the prevention of cardiovascular or heart disease, which is a global health burden and the commonest single reason for deaths, causing 3 in every 10 deaths in 2008.
We wanted to do the review because there is a lot of evidence from non-randomised studies that suggests a link between the intake of vitamin C and cardiovascular or heart health. But, whether this holds true when the vitamin is tested in randomised trials was not clear.
We found only 8 such studies, that had included more than 15,000 people and were done in the US, Europe and South Africa. These 8 randomised trials looked at vitamin C supplementation as a single ingredient taken by people at high risk of cardiovascular or heart disease, or by healthy people, and compared it to placebo, or a dummy tablet. We had hoped to look at the impact on important clinical endpoints such as heart attacks, strokes and deaths but only one of the trials reported on this and it found no effect of taking vitamin C. This was a large trial, with more than 14,000 participants and was carried out over 8 years. However, it included a selected population of middle-aged men, so we can’t generalise the results to the rest of the population.
The other 7 trials were much smaller and short term. They looked at the effects of vitamin C on things such as blood pressure and lipid levels, and produced inconsistent results which means that we can’t draw any firm conclusions at present.
Overall, the quality of evidence was low or very low. This needs to be addressed by more high quality, larger trials conducted over longer periods of time and, while we wait for that research, we wouldn’t recommend anyone rushes out to buy vitamin C specifically to prevent cardiovascular disease, because the evidence to support this is not available at present. However, in the two studies that reported side effects, these were not different between the vitamin C and placebo groups, which is in line with other studies in other conditions that show that the side effects of taking vitamin C are rare. Therefore, because taking vitamin C is unlikely to cause harm and because it has been shown to have other benefits, people might still wish to try it.

John: If you would like to read specifically about the evidence on vitamin C and cardiovascular disease, this Cochrane Review can be found online. Just visit Cochrane Library dot come and search 'vitamin c and cardiovascular disease'.

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