Telomere length (ratio) and years since their child's diagnosis with chronic
illness.
Arguments
source
Epel, E.S., E.H. Blackburn, J. Lin, F.S. Dhabhar, N.E. Adler, J.D.
Morrow, and R.M. Cawthon. 2004. Accelerated telomere shortening in response
to life stress. Proceedings of the National Academy of Sciences (USA)
101: 17312-17315.