I have stated many times that I consider 200 mcg to be too much selenium on a long-term basis. I have long thought that 100 mcg or less is probably going to deliver all the benefits anyone could expect, and selenium is well-known to be toxic in even moderate excess. (Though it is quite possible that someone who is actually significantly deficient might need a "loading dose" to correct the deficiency before switching to a maintenance dose. I don't know!)
Today we see the Guardian reporting this:
Some vitamin supplements raise risk of cancer in men, research shows
Clinical trials show high levels of the mineral Selenium can raise chances of developing high-grade cancer by 91%
theguardian.com/society/201...
The story also involves vitamin E supplements - which seems to be intimately related to selenium.
Do read the comment by Dr Matthew Hobbs, deputy director of research at Prostate Cancer UK.
(Only a few years ago, selenium was being touted as a preventative measure against prostate cancer. Though I never felt that I had found any proper evidence as to which form of selenium was supposed to work - some claiming only inorganic forms, others seeming not to differentiate.)
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Rod
When to take Selenium
When to take zinc, selenium supplements
Signs of excess selenium
Selenium 50mcg recommendation 
