I read about
this, I've always got bend in some nails, although not a dip, the other way around that nails curve over on index and middle finger. Think what you are talking about
is "clubbing"? I have read can signify lung problems and celiac?
Nails were looked at closely in medicine before the modern world. Summary of the old beliefs here, probably something in a lot of itwww.naildoctors.com/nail_health.html
Or maybe this is spooning sorry, not clubbing "Spoon shaped Nails: Iron deficiency; thyroid disease " Would make sense if we were iron deficient in flare