The soil in Australia, especially in many of the coastal regions, is low in selenium. Here is an article from a conservative/conventional group that warns selenium levels may be low in the Australian population.

If the food supply is low in selenium, then one has to be particularly careful about diet. One also has to be particularly careful about exposure to mercury. (Mercury will get rid of your selenium, molybdenum and sulfur.)

People with various cancers seem to be helped if their selenium levels are raised. (Look up the studies in the NIH data base for your specific cancer.) For instance:

Here is a study of modest selenium and zinc supplementation for patients undergoing chemotherapy due to intestinal cancer. (Selenium and zinc helped with the weakness and appetite.)

Here is a study of selenium supplementation for patients undergoing chemotherapy for leukemia. (Selenium helped reduce the mouth soreness.) "The efficacy of selenium in prevention of oral mucositis in patients undergoing hematopoietic SCT: a randomized clinical trial."

Here is a study of initial selenium levels in patients undergoing chemotherapy for aggressive non-Hodgkins lymphoma. (Higher selenium levels before chemotheraphy meant that the outcome was better. )“Serum selenium concentration at presentation is a prognostic factor, predicting positively for dose delivery, treatment response, and long-term survival in aggressive non-Hodgkin's lymphoma. Unlike most existing prognostic factors in aggressive non-Hodgkin's lymphoma, selenium supplementation may offer a novel therapeutic strategy in this frequently curable malignancy.”

A good source of selenium is seafood. However, certain fish are high in mercury. Swordfish, ahi tuna and king mackeral have the highest levels of mercury. Canned Albacore tuna is high in mercury. Canned chunk light tuna is in the middle. Wild Salmon, tilapia, and shrimp are low in mercury. Here is a more extensive list:

The other common source of mercury exposure is amalgam “silver” fillings in teeth. On average, these fillings are 50% mercury. The release of mercury from these fillings can be easily demonstrated upon rubbing them, or exposing them to warm water. Chewing gum and drinking hot coffee/tea is not recommended when you have mercury in your mouth. It will just increase your exposure.

Mercury will get rid of your selenium. On the other hand, selenium will get rid of mercury in the body. Unfortunately, sometimes people are so mercury toxic, that they can't tolerate selenium supplementation. The selenium moves the mercury out of the tissue, but it doesn't escort it completely out of the body. One way to mitigate a reaction to selenium is to take things to absorb the mercury being dumped into the intestines. The most popular of these among cancer patients is modified citrus pectin. Note: sometimes people will tolerate a form of selenium called selenite, but not methylselenocysteine. Yet the selenocysteine form may be more effective for some cancers. Also, there are other ways to help usher mercury out of the body, but a discussion of that would not be appropriate for this forum.

I know this forum is very wary of any type of supplementation. In the case of selenium, caution is warranted, because too much can be a problem. However, if you live in Australia, have mercury “silver” amalgam fillings, or have been eating a lot of the wrong fish, then you should at least get your selenium levels measured. If the levels are low, consider supplementation. Perhaps add modified citrus pectin if you suspect too much mercury in your body. If you don't want to take pills, the selenite form is available as a liquid from Nutricology.