Better targeting and/or better images. Why test 1 image if you can test dozens at the time? Images are really key for a good CTR! Remember coming weeks/months are HOT HOT HOT regarding nutra, so you have to beat the heavy competition with real interesting stuff!
Hey buddy, I find that your replies are really useful and I learned a lot from you. Are you saying to keep testing new images till I get low CPM/CPC? Yes I do agree coming weeks nutra will be competitive.
Things to never, ever underestimate in AM:
1) Effects of a good angle.
2) Effects of split-testing offers between networks.
3) Effects of finding one or more really good images, even if you have to test a hundred to do it.
70$ per cpm? that's really high!
Test and find out better targeting & more attractive creative. And your CPM/CPC will go down.
BTW I'd like to ask how long dose your fb accounts live?
This is called ''affiliate rip and run effect''. Most likely you have 10+ other nutra affiliates using same targeting(maybe also ad copy) and that makes prices high with such nice CTR's, as you all are bidding for same 1.2m demo 
There is one more theory I heard, not sure how valid. Facebook sometimes bans ad copies, instead of accounts. They are linking trending fake news ad copies and flag them without actually banning you. So end of day, affiliates can't be profitable with them and quit running it even when you have ctr's of 15+, you will pay same amount as 4 ctr ad copy.
Consider also feedback - generally negative feedback will bring cpc's up even when your rel score is 10.