I’m reading through a lot of very wordy guidelines and information sources from the National Agriculture Library, and I came across this PDF describing the elements in the title. The tl;dr is that no RDA is set for any of these, but it’s shown that you can be deficient in them.
I’ve made a short summary of the information in the PDF:
Arsenic Deficiency effects exist. Normal diet: Men: 2.0-2.9 µg, Women: 1.7 - 2.1 µg. No UL set, but intake probably comes from water already
Boron Deficiency effects exist. Normal diet: 0.87 - 1.35 mg. UL 20 mg
Nickel Deficiency effects exist. Normal diet: 74 to 100 µg, or 207 to 406 µg. UL 1 mg of soluble nickel salts
Silicon Deficiency effects exist (bone formation). Normal diet: 14 to 46 mg. UL Unknown
Vanadium Deficiency effects exist. Normal diet: 6 to 18 µg. UL 1.8 mg elemental vanadium
So, some people already add Vanadium, but the usual amount (100µg) seems high compared to a normal diet. I’ve seen Boron mentioned, but not a lot. Arsenic probably comes wholly from tap water. The other two are hardly mentioned.
What are your thoughts on this?
PS: More info than you ever wanted to know about more nutrients than you have looked at so far: http://fnic.nal.usda.gov/dietary-guidance/dietary-reference-intakes