Spit: saliva in nursing research, uses and methodological considerations in older adults.

Over the last 10 years, interest in the analysis of saliva as a biomarker for a variety of systemic diseases or for potential disease has soared. There are numerous advantages to using saliva as a biological fluid, particularly for nurse researchers working with vulnerable populations, such as frail older adults. Most notably, it is noninvasive and easier to collect than serum or urine. The authors describe their experiences with the use of saliva in research with older adults that examined (a) osmolality as an indicator of hydration status and (b) cortisol and behavioral symptoms of dementia. In particular, the authors discuss the timing of data collection along with data analysis and interpretation. For example, it is not enough to detect levels or rely solely on summary statistics; rather it is critical to characterize any rhythmicity inherent in the parameter of interest. Not accounting for rhythmicity in the analysis and interpretation of data can limit the interpretation of associations, thus impeding advances related to the contribution that an altered rhythm may make to individual vulnerability.