Recent work in young and middle-aged subjects suggests that
melatonin levels in saliva may represent a viable alternative to serum
melatonin measurement. We hypothesized that it may be a valid measure of
melatonin levels in older adults as well, but features unique to the elderly may limit its utility. To study this, subjects were admitted to an academic medical center where saliva and serum specimens were collected concurrently in dim light conditions during a 14-hr overnight study period and analyzed for
melatonin levels with radioimmunoassays (RIAs). Eighty-five subjects over the age of 65 with a broad range of medical conditions participated in the study. Subjects with
dementia, depression and
anemia were excluded. We found that saliva volume was inadequate for analysis (<200 microL) in 23.6% of specimens, with the majority of inadequate volume specimens occurring after midnight and inadequate specimens occurring more frequently in females than in males. The correlation coefficient for saliva
melatonin and serum
melatonin was r = 0.659 (Spearman, P < 0.001), and r = 0.466 for saliva dim light
melatonin onset (DLMO) and serum DLMO. Saliva
melatonin levels were 30.9% of serum
melatonin levels, with a wide range of ratios noted between subjects. Overall
melatonin levels influenced both the correlation and ratio of saliva
melatonin to serum
melatonin; higher correlations and lower ratios were noted when
melatonin levels were high. Saliva specimens provide an economical and practical method for
melatonin assessment, however, in older adults, issues such as
hyposalivation and low
melatonin levels limit the feasibility and validity, respectively, of saliva
melatonin.