well there is that old wives' tale isn't there. got a snippet of research backing that up:
Lower serum zinc in chronic fatigue syndrome (CFS): relationships to immune dysfunctions and relevance for the oxidative stress status in CFShttp://www.ncbi.nlm.nih.gov/pubmed/16338007http://cfids.best.vwh.net/cfs-inform/Hy ... etal05.pdf
"For example, leukonychia (white spots on finger nails) is one of those characteristics for CFS pointing towards lowered zinc."
can't readily find a straight up study on serum zinc levels in folks with leukonychia though.
when my nutrient status is bad i get an early warning from my nails. in recent yrs i have the most lovely nails I've had in my entire life. when i was a teenager i used to sand out the dents. before during and after dx, my nails were atrocious, practically falling off. i had bare nail bed in places. hate seeing this on others and having to bite my tongue.
since doing all this work with nutrition it's just night and day. fixing your zinc level will probably make a big difference. but there are a few other levels to worry about of course. i'm not sure all of them have to do with fingernails, but some will.