You should not take selenium pills indiscriminately because taking too much selenium causes nerve damage, vomiting, nausea, feeling sick, white ridges on nails, hair loss, mottling of teeth, and loss of nails. Therefore you need to interpret the data correctly or you could poison yourself and shorten your life. The association between low tissue levels of selenium and prostate cancer could be that men are doing something that causes prostate cancer and also causes them to have low levels of selenium. Whole grains are a seed that has a thick coat called the husk. It is filled with endosperm that contains starch as a food for the germ that is the baby plant inside the seed.
Selenium is found in the germ of grains.
It is not found in the endosperm. Bakery products and pastas are made from flour that is made by removing the germ with its selenium and grinding the endosperm to make the flour. So commercial flour does not contain measurable amounts of selenium unless it is made from whole grains. So men with low tissue levels of selenium are the ones who do not eat whole grains. The germ also contains all the Energy B vitamins, almost all other minerals such as chromium, zinc, and so forth, and much of the phytochemicals that prevent disease.