<2007 “Vitamins Could be Killing You: Vitamin supplements designed to prevent disease might actually increase the risk of death, a landmark global study has found. Vitamin A performed worst in the 68-trial review and is said to increase mortality risk by 16 per cent. . . University of Queensland professor Luis Vitetta, from the Centre for Complementary Medicine and Research, said the results were ‘very concerning’ and added strength to evidence vitamins can do more harm than good.”—‘Daily Telegraph,’ 1 March>
To the U.S. American ear (or at least to my U.S. American ear) the use of CONCERNING as a participle adjective, as in VERY CONCERNING, is a strange-sounding locution. The only use that I am familiar with is as a preposition meaning relating to, regarding, about, as in “a discussion concerning foreign aid.”
In the Oxford English Dictionary the participle adjective is listed as having two meanings, the first of which is said to be archaic:
CONCERNING participle adjective: 1)  That is of concern, that gives cause for consideration; important, weighty. archaic. 2)  That gives cause for anxiety or distress.
However, the 1741 quote is the only quote under the second meaning (apparently not considered archaic), which made me wonder just how much this form is used today. Checking a few U.S. dictionaries I found that Merriam-Webster’s Unabridged Dictionary lists the participle adjective but only as archaic: giving concern, important. And Random House Unabridged Dictionary and American Heritage Dictionary don’t list it at all.<1741 “I cannot bear anything that is the least CONCERNING to you.”—‘Pamela’ by Richardson, II. page 158>
A U.K Google search for the term VERY CONCERNING produced ~ 97,000 hits; an Australia search produced ~ 15,000 hits; a New Zealand search ~ 1800. Looking at hits with respect to population, the widest use is in the U.K. which is about twice that of Australia, which is about four times that of New Zealand, which is over 200 times that of the U.S. So it is not unheard of in the U.S. but it’s relative use is mighty skimpy. In fact, in a search of U.S. newspapers, I got a paltry ~ 200 hits for newspapers dating back to the 19th century, which is bupkis (Yiddish for ‘beans,’ but, ultimately, according to my grandfather who came from the old country, it meant ‘goat shit’).
So, my conclusion is that although the participle adjective CONCERNING, as in VERY CONCERNING, is deemed archaic or even obsolete by by some U.S. dictionaries, it is still used here but ever so little. In the U.K., however, and according to the OED, it is not archaic and seems to be fairly common but less so in Australia and New Zealand.. But folks living in these countries might have a better feel for this than I do.
For the benefit of those who, as myself, are unfamiliar with the use of CONCERNING in this way, here are some more examples (including one’s from the U.S., but one never knows if the person using it here is native born) that I found in newspaper archives:
Ken G – March 21, 2007<2001 “"It's VERY CONCERNING," said Travis Vallin, director of the Colorado Division of Aeronautics. "Without a doubt, rural airports, small community airports, are hurting. Without a doubt, it's VERY CONCERNING." ‘Denver Post,’ 29 October>
<2003 “How can something like this occur in this day and age, in the year 2003, where it seems that an inmate can simply pop a window out of the prison, climb out and run away? Lupas said ‘That’s very alarming, very discouraging and VERY CONCERNING to me.”—‘Intelligencer’ (Doylestown, Pennsylvania),12 October, page 117>
<2006 “There is a lot of intelligence that requires investigation, some of it is very sinister. It is a VERY CONCERNING intelligence picture - that is the simple and honest way of putting it."—‘Telegraph,’ 7 May
<2006 “In the run-up to the first anniversary of the July 7 bombings, Peter Clarke, the head of the anti-terrorist branch, said intelligence surrounding the terrorist threat was ‘very, VERY CONCERNING.’”—‘Guardian,’ 3 July>