1. Do plasma melatonin concentrations decline with age?
Germaine Cornélissen, PhD, Franz Halberg, MD, Naoto Burioka, MD, Federico Perfetto, MD, Roberto Tarquini, MD, Earl E Bakken, DSc 
The American Journal of Medicine 
Volume 109, Issue 4, Pages (September 2000)
DOI: /S (00)

2. Figure
In data taken from a published graph (1), a smaller circadian amplitude can be demonstrated in older subjects when the data have been log10-transformed, but not when they are expressed in original units.
The American Journal of Medicine  , DOI: ( /S (00) )