I'm aware that one women reported taking selenium supplements and started loosing her hair. They later found out that the company who made it was accidentally doing a mathematical error in the calculation of the product and in it's formulation it had exactly 100x the amount of selenium listed on the bottle. A 200mcg pill became 20000mcg pill.
In circa 2010 when I was reading Protégez-vous magazine, they tested many dozens of brands of Vitamin D3 and found out that the content of stated vitamin D3 on the bottle varied from -50% to +10%.
Also, I have read someone say that zinc, copper, Iodine and selenium work together (Please note: This person stated that all 4 had not been studied together yet). Also, hair loss is a sign of copper deficiency.