Originally posted on PSI-CHI.
Close your eyes and imagine sour foods, like sour gummy candies or lemons… notice anything? If you felt a mouthwatering sensation you’re not alone. In fact, I commonly suggest that participants imagine eating something sour to aid in saliva sampling. Although the integration of saliva in psychological research emerged in the 1990s, the pandemic really highlighted the usefulness of noninvasive biospecimen, such as spit. In a recent interview (Coker, 2022), Dr. Michael Hoyt, the Director of the Institute for Interdisciplinary Salivary Bioscience Research (IISBR) at the University of California, Irvine, boasted about the benefits of using saliva saying, “It’s not invasive. We don’t have to stick someone with a needle. You know, COVID furthered the dialogue.”
As scientists grappled with pandemic-related restrictions in 2020, ethical concerns arose regarding participant and researcher risk of viral infection when coming into the laboratory. Many scientists approached barriers to data collection with innovative revisions to existing protocols, including utilizing self-collection procedures for biospecimens. Both the approachability of self-collection and the expansion of the field of salivary bioscience have facilitated advancements in scientists’ ability to pursue novel and complex research questions. Namely, the inclusion of salivary biospecimens in psychological research has supported research questions that include multiple levels of analysis (e.g., psychosocial and biological). Studies that utilize multiple levels of analysis are critical in advancing the field and augmenting the generalizability of study findings (Farre & Rapley, 2017; Suls et al., 2013; Suls & Rothman, 2004).
Opportunities in salivary bioscience have helped pave the way for new empirical questions in traditionally nonbiology-related subfields, such as in social psychology, giving researchers the ability to explore factors that explain how biology, psychology, and well-being are related (Hamilton et al., 2022). For example, a researcher could assess changes in stress hormones following a social evaluative stressor among women with posttraumatic stress disorder (Metz et al., 2020). Alternatively, one could investigate alterations in inflammatory markers among depressed individuals (Yui et al., 2022). In this way, researchers can make use of an objective measure to understand how psychological processes get under the skin to affect health.
Why Saliva?
Many researchers find salivary measures appealing because a wide range of analytes (i.e., biological measures that can be indexed from saliva) can be obtained from a single sample. Such analytes include hormones, and markers of inflammation, sleep, cellular aging, and even the epigenome. Saliva can also index diversity within the oral microbiome, infection, the presence of COVID-19 antibodies, and harmful environmental exposures further expanding the levels of analysis made possible with spit. Dr. Jenna Riis, Assistant Professor of Kinesiology and Community Health at the University of Illinois at Urbana Champaign, stated in a recent interview (Coker, 2022), “[Saliva] allows me to examine the body’s response to adversity by looking at changes in multiple physiological systems dynamically across time and with minimal burden to my participants”. Most famously, salivary analytes like cortisol have been used to assess acute physiological stress responses, indexing how stress-related systems activate and then recover following a laboratory stressor task or a natural stressor experienced in the real-world.
Given the wide range analytes that can be obtained from spit, it is no surprise that the inclusion of saliva in psychological research may foster interdisciplinary work, where experts within the various subfields of psychology can collaborate with endocrinologists, biomedical engineers, statisticians, and clinicians to advance science in new ways. Dr. Hoyt contends (Coker, 2022), “I couldn’t do this [research] without talking to my medical collaborators, with my immunology colleagues, social scientists, public health professionals, my biology folks. It takes that team.” Benefits are also seen regarding participant burden, acceptance, and adherence as there is evidence that suggests that saliva sampling may have higher acceptance compared to other more invasive biological sampling methods, which could help support diversity among research participants.
Another notable benefit is that which with some training, saliva can be collected by participants at nearly any feasible location (e.g., at home, work, school), mitigating the need for a traditional laboratory environment and increasing the ecological validity of the measurement. Importantly, because of how easily spit can be obtained, it allows for the collection of multiple samples within a short amount of time. Dr. Riis highlights this benefit saying (Coker, 2022), “Because saliva can be self-collected in the field, salivary bioscience provides unique opportunities to learn about the health and well-being of communities in real time—making the potential application of salivary bioscience to health surveillance, monitoring, assessment and interventions very exciting.”
Being able to collect biospecimens in this way is particularly useful with dyadic research, where an investigator may be interested in collecting biospecimens from multiple participants at the exact same time, such as in mother–child or spouse–spouse dyads. In relation to acceptability and adherence, saliva collection is often preferred among child participants, where passive drool (the gold standard for saliva collection, which involves drooling into a vial with a straw) is far more attractive than a needle.
Things to Consider
The inclusion of saliva in psychological research requires several considerations at the research design, data collection, sample processing and analytic phases. First, time of day, time of waking, and time between saliva samples are important details when investigating biomeasures that are affected by diurnal and circadian rhythms (e.g., melatonin). Second, researchers should consider the method of collection (e.g., passive drool vs. oral swab), the collection device type, and the number of samples to be collected. Investigators must also decide how they will transport samples and what their long- and short-term storage options will be. Some analytes such as testosterone require the coldest of environments, where -80°C is recommended for long-term storage. These decisions can greatly impact the costs associated with saliva collection and will inform the types of research questions that can be pursued. Dr. Hamilton and colleagues (2022) have previously detailed additional considerations surrounding saliva collection procedures that will be especially helpful for junior scientists who are in the development stages of their research projects. Finally, data management and statistical approaches that are unique to salivary data are critical to project success.
Advances in statistical approaches have expanded the usefulness of saliva in psychological science. To illustrate, growth curve modeling and group-based trajectory modeling may be fitting for salivary data as these techniques allow for the investigation of analyte change over the course of a day, a laboratory visit, or even across the life-course. Researchers can investigate this change both within individuals (i.e., how one individual changes from baseline) and between individuals (how groups of individuals compare in their change from baseline). Fortunately, the vast increase in research that includes salivary measures has inspired a wave of publications that inform investigators of the various analytic approaches in handling salivary data (Ahmadi et al., 2021; Riis, Ahmadi, Hamilton, Bryce, et al., 2021; Riis, Ahmadi, Hamilton, Hand, et al., 2021; Segerstrom & Boggero, 2020). Students who are interested in this line of work should seek workshops and courses, such as free webinars offered by the American Psychological Association, that teach various statistical approaches for repeated measures data.
Tips for Junior Researchers Interested in Salivary Bioscience
This blog post aims to illuminate supportive resources for Psi Chi members who are considering the vast options in psychological research and points to one avenue that may support the development of innovative research ideas. If you are a student who is considering graduate school and you wish to gain detailed instruction in salivary bioscience, consider seeking graduate programs with specialized training, such as the University of Nebraska-Lincoln, the University of Wisconsin-Maddison, Penn State University, or the University of California, Irvine—all of which house saliva wet labs. Furthermore, as junior scientists, we are conscientiously weaving together components of our academic agenda; knowing what options exist can help us make decisions about the types of training we will need for our desired careers, including choosing the right statistical courses and seminars that will expand our investigative proficiencies. Because research with salivary measures often facilitates interdisciplinary collaboration, I suggest students consider learning strategies, such as team science approaches, to support building relationships across disciplines. This interdisciplinary relationship building could not only help increase the impact of your work but could also help with networking when seeking post-doc or post-grad positions. Finally, research projects that include biological/physiological measures in tandem with psychosocial measures align with values of several funding agencies like the National Science Foundation and the National Institutes of Health, which may be especially advantageous for junior researchers interested in predoctoral and doctoral fellowships from these agencies. Importantly, these fellowships tend to offer higher stipends than what may be offered from a given university and are typically funded throughout the summer months. In some cases, a stipend is available to support student research, which could help fund the inclusion of salivary measures.
Conclusion
Salivary bioscience is a fast-developing tool for psychological research that will contribute to major advancements in the field and to the generalizability of results. Because of its minimally invasive nature, saliva sampling may enhance diversity of participants more so than other biospecimen sampling methods. The field of psychology is growing in new and exciting ways, augmenting graduate training to allow for the inclusion of biological measures like saliva will prepare the next generation of scientists to meaningfully contribute to empirical research.
Psi Chi members interested in learning more may look to the resources linked in this blog post. In particular, the historical summary by Hamilton et al. (2022) is a great place to start.
References
Ahmadi, H., Granger, D. A., Hamilton, K. R., Blair, C., & Riis, J. L. (2021). Censored data considerations and analytical approaches for salivary bioscience data. Psychoneuroendocrinology, 129. https://doi.org/10.1016/j.psyneuen.2021.105274
Coker, M. (2022). Window into the body. IISBR researchers champion the use of spit in diagnostics. UCI School of Social Ecology. https://socialecology.uci.edu/news/window-body
Farre, A., & Rapley, T. (2017). The new old (and old new) medical model: Four decades navigating the biomedical and psychosocial understandings of health and illness. Healthcare, 5(4), 88. https://doi.org/10.3390/healthcare5040088
Hamilton, K. R., Granger, D. A., & Taylor, M. K. (2022). Science of interdisciplinary salivary bioscience: History and future directions. Biomarkers in Medicine, 16(14), 1077–1087. https://doi.org/10.2217/bmm-2022-0452
Metz, S., Duesenberg, M., Hellmann-Regen, J., Wolf, O. T., Roepke, S., Otte, C., & Wingenfeld, K. (2020). Blunted salivary cortisol response to psychosocial stress in women with posttraumatic stress disorder. Journal of Psychiatric Research, 130, 112–119. https://doi.org/10.1016/j.jpsychires.2020.07.014
Riis, J. L., Ahmadi, H., Hamilton, K. R., Bryce, C. I., Blair, C., & Granger, D. A. (2021). The case for the repeatability intra-class correlation as a metric of precision for salivary bioscience data: Justification, assessment, application, and implications. Psychoneuroendocrinology, 128. https://doi.org/10.1016/j.psyneuen.2021.105203
Riis, J. L., Ahmadi, H., Hamilton, K. R., Hand, T., & Granger, D. A. (2021). Best practice recommendations for the measurement and interpretation of salivary proinflammatory cytokines in biobehavioral research. Brain, Behavior, and Immunity, 91, 105–116. https://doi.org/10.1016/j.bbi.2020.09.009
Segerstrom, S. C., & Boggero, I. A. (2020). Expected estimation errors in studies of the cortisol awakening response: A simulation. Psychosomatic Medicine, 82(8), 751–756. https://doi.org/10.1097/PSY.0000000000000850
Suls, J., Krantz, D. S., & Williams, G. C. (2013). Three strategies for bridging different levels of analysis and embracing the biopsychosocial model. Health Psychology, 32(5), 597–601. https://doi.org/10.1037/a0031197
Suls, J., & Rothman, A. (2004). Evolution of the biopsychosocial model: Prospects and challenges for health psychology. Health Psychology, 23(2), 119–125. https://doi.org/10.1037/0278-6133.23.2.119
Yui, S., Sasayama, D., Yamaguchi, M., & Washizuka, S. (2022). Altered levels of salivary cytokines in patients with major depressive disorder. Clinical Neurology and Neurosurgery, 221, 107390. https://doi.org/10.1016/J.CLINEURO.2022.107390
