Several nutrients and other food components have been suggested to specifically protect against certain cancers, but the evidence is too weak to recommend them for cancer prevention – these include selenium, lycopene, and vitamin D. Intervention studies that have tested these dietary supplements and other nutrients have not established any benefit, and sometimes have found unexpected harm, especially when high doses are used; therefore, it is not recommended to take dietary supplements for cancer prevention. It is best to have a diet of ordinary foods that will provide all the nutrients you need.

There are circumstances when dietary supplements might be valuable – such as folic acid for women planning to become pregnant, or vitamin D for people at risk of deficiency; your doctor can advise you about this.

If you have already been diagnosed with cancer, don’t take any supplements without first checking with your doctor – some have been shown to interfere with cancer treatments.