Eating selenium rich foods including shellfish, nuts and onions, decreases the risk of liver cancer say scientists.
Two comprehensive meta-analysis of selenium studies do not support the claim that eating selenium rich food decreases the risk of liver cancer.
Websites such as liverdoctor.com ‘urge’ people to increase selenium intake (via their branded liver supplement) to help reduce the risk of liver cancer. This is based on a single study which showed that people with liver cancer were more likely to have lower blood selenium levels (2, 4).
The fact that people with liver cancer are more likely to have lower selenium blood levels does not necessarily mean that increased selenium intake will actually reduce the risk of liver cancer.
There are two Cochrane overviews which effectively answer the question about the relationship between liver cancer and selenium.
The first Cochrane review of interest was published in 2015 and evaluated all studies looking at selenium and cancer (3). They identified 55 observational studies of more than 1,000,000 people. These studies found an overall lower cancer risk in people who took selenium. The lower risk of cancer was noted for cancers of the stomach, bladder and prostate but not for cancer of the liver.
This Cochrane review also identified 8 randomized control trials with a total of 4473 participants. Data from randomized control trials is considered to be more reliable than observational data. It is like the popular kids game of ‘rock, paper, scissors’ and randomized control trials trump observational data every time.
The meta-analysis of the randomized control data showed that selenium supplementation did not reduce the risk of any cancer. In fact, it did show that the risk of non-melanoma skin cancer was actually increased.
The first Cochrane review raises concerns about the safety profile of selenium and especially mentions a possible increased risk of type 2 diabetes, alopecia and dermatitis.
The second Cochrane review looked at antioxidant supplementation which included selenium for liver disease (1).The overview did not focus exclusively on liver cancer but did include liver cancer in the overall health outcome measures.
In this second overview, the researchers identified 20 randomized control trials of 1125 participants with cirrhosis, alcoholic hepatitis, autoimmune hepatitis, viral hepatitis B or C.
This comprehensive meta-analysis found no convincing evidence that antioxidants, including selenium, reduced the risk of liver cancer.
Pharmaceutical companies provided the selenium supplementation in at least 10 of the 20 trials evaluated. Again the reviewers raised concerns about the safety profile of selenium as they noticed that selenium may actually cause a deterioration in liver enzyme blood test results.
In summary, there is no evidence to support the claim that selenium supplementation reduces liver cancer risk or overall liver health outcomes.