Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. There are several Cochrane Reviews of the effects of a class of drugs called antioxidants, covering a wide range of health conditions. One of these, focused on adults with chronic kidney disease, was updated in November 2023. In this podcast, Julia Colombijn, talks with fellow author, Robin Vernooij, both from the University Medical Center Utrecht in the Netherlands, about the topic and the findings of the review.

Robin:  Hello Julia, thanks very much for talking with me today. Perhaps you could begin with a few words about antioxidants. What are they and how do they work?

Julia: Hello Robin. It's a pleasure to be here. Antioxidants are a group of substances that are found in various foods and can also be taken as supplements. They encompass a wide range of compounds such as beta carotene, selenium, flavonoids, and vitamins; and they reduce oxidative stress by neutralizing harmful molecules called reactive oxygen species.

Robin: Thanks. So, how might they help adults with chronic kidney disease and why did you do this Cochrane review?

Julia: Oxidative stress plays an important role in cardiovascular disease and patients with chronic kidney disease have elevated oxidative stress levels, which means that if antioxidants reduce this oxidative stress, they might reduce the risk of cardiovascular and kidney disease. Therefore, we did this Cochrane review to find this out, by examining the effects of antioxidant therapy on death and cardiovascular and kidney disease in adults with chronic kidney disease, including patients receiving dialysis, and those who had had a kidney transplant.

Robin: And what did you find?

Julia: In brief, the review shows that antioxidants may have little to no effect on cardiovascular death and probably do not reduce the risk of premature death in patients with chronic kidney disease. However, they probably do reduce the risk of cardiovascular disease and likely reduce the risk of kidney failure. We also found that antioxidants slowed down kidney function decline but may have little to no effect on urinary albumin/creatinine ratio, which is one of the markers for chronic kidney disease.

Robin: What about the harms, did you find any adverse effects of antioxidants?

Julia: Yes. Alongside a possible reduction in the risk of cardiovascular disease and kidney failure, there are some concerns about possible side effects. For example, in some studies, antioxidants increased the risk of heart failure and serious infections.

Robin: Thanks Julia. Very interesting. To finish, how should these findings be used in clinical practice and how can listeners find out more?

Julia: Firstly, people need to interpret the results of our review with caution. The information on the effects of antioxidants on cardiovascular and kidney outcomes in patients undergoing dialysis or kidney transplant recipients remains limited because few studies included these patient populations. Also, the quality of the included studies was generally suboptimal, the duration of follow-up was short and we could not compare different antioxidants with each other. Therefore, without randomised trials of adequate quality and follow-up, it's still difficult to make recommendations about the application of antioxidants in clinical practice, and we discuss this need more fully in the review which is available from Cochrane Library dot com with a search for 'antioxidants and chronic kidney disease'.