Dr. Harfmann's Research Group

Overview

Dr. Brianna Harfmann’s group will investigate potential modulators of human circadian rhythms. Circadian rhythms are oscillations in physiological and behavioral processes which occur over approximately 24 hours (Ko & Takahashi, 2006; Miller et al., 2007). These rhythms are essential for human health, as disruption of rhythms is associated with development of pathologies including diabetes, insomnia, cardiovascular disease and cancer (Crnko et al., 2019; Hasan et al., 2018; Peng et al., 2022; Zhou et al., 2022). Circadian rhythms are set and maintained by the mammalian molecular clock, which exists in all cells of the human body. While every tissue has its own clock, the peripheral clocks are regulated and synchronized by the master clock in the suprachiasmatic nucleus of the hypothalamus (Mohawk et al., 2012). These clocks are capable of free-running, meaning they will continue to keep time without any external cues. However, several cues, such as light, activity, and feeding, are known to serve as entrainment factors (Daas & De Roos, 2021; Hughes et al., 2021; Thomas et al., 2020; Vasey et al., 2021).

While a number of entrainment factors have been established, new factors continue to be discovered. One possible entrainment factor is vitamin D. Vitamin D receptors are highly expressed at the master clock, the suprachiasmatic nucleus (Jung et al., 2019). Plasma vitamin D levels have been shown to be inversely related to melatonin, a supplement commonly used to treat circadian disruption from jet lag (Golan et al., 2013). Vitamin D levels are also associated with sleep-wake cycles, a primary example of a circadian rhythm. Low vitamin D levels correlate with reduced sleep duration and quality, and vitamin D supplementation in individuals with sleep disorders results in improved sleep (Majid et al., 2018). Despite this evidence, there is a lack of research investigating the effect of Vitamin D on circadian rhythms. Therefore, the purpose of this study is to evaluate the relationship between vitamin D and circadian rhythm parameters.

In our work, research subjects will be asked to take vitamin D supplements (4000 IU/day) or a placebo each morning for 2 weeks. Pre- and post-supplementation data will be obtained on plasma vitamin D levels and circadian parameters. Briefly, blood spots will be taken and used to quantify vitamin D using HPLC (Keyfi et al., 2018) and subjects will wear an ActTrust2 wristband (Condor Inc.) to evaluate circadian rhythmicity, strength and timing. Plasma vitamin D levels and circadian data will be analyzed to identify correlations. Additionally, pre- and post-data will be compared to determine whether vitamin D supplementation influences circadian rhythm parameters.

RESS Participant Experiences

The primary SEPs employed by RESS participants during this research include: (1) asking questions and defining problems; (2) planning and carrying out investigations; (3) analyzing and interpreting data; (4) constructing and designing solutions; and (5) obtaining, evaluating and communicating ideas. Participants will help with recruitment of subjects and collection of data. They will gain CITI certification and learn how to properly conduct human subject research. Participants will learn how to collect, record, store and analyze data. They will be asked to pull on their understanding of material to interpret findings and potentially formulate new questions to guide further analysis. An important part of research is dissemination of information. As such, work from this project will be submitted for presentation at regional (Michigan ACSM or Michigan Physiological Society) and national (American College of Sports Medicine or American Physiological Society) meetings. Participants will be involved in the preparation of abstracts, development of presentation materials, and the presentation itself, as has been standard practice for prior research assistants in Harfmann’s lab.