A woman’s blood sugar response to a morning run may differ from her response to an evening run, and that difference may shift depending on where she is in her menstrual cycle. Current exercise guidelines largely ignore menstrual cycle phase and time of day, even though hormonal fluctuations are known to alter insulin sensitivity. Glucose control worsens in the luteal phase compared with the follicular phase, yet no one has systematically tested whether timing exercise could offset that effect. This project will recruit about 50 people with regular cycles, use wearable glucose monitors and a novel app to track sleep, activity, mood, and food intake, and compare glycaemic outcomes after exercise performed at different times of day in both cycle phases. If the hypothesis holds, the findings could lead to personalised exercise timing recommendations—simple, no-cost adjustments that help people maintain metabolic health, particularly those with inflexible schedules such as shift workers or carers. The research is fundamentally exploratory: it asks a basic question about how two biological rhythms—circadian and menstrual—interact to shape metabolic responses. Understanding that interaction is a necessary first step before any practical guidance can be developed.
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The menstrual cycle is a multifaceted process regulated by hormones that fluctuate throughout the cycle, and this can have an impact on circadian rhythm and glycaemic control. Studies suggest that glycaemic control is worse in the luteal phase of the menstrual cycle than in the follicular phase. This is thought to be due to ovarian sex hormone level fluctuations during the menstrual cycle, as these changes can affect insulin sensitivity. Exercise is beneficial for insulin sensitivity, metabolic health and is normally observed to improve glycaemic control. However, we have previously shown that the time of day that exercise is performed can influence glycaemic outcomes. Understanding how glycaemic regulation in response to exercise timing may be altered during the menstrual cycle has important implications for exercise recommendations to people across a large age range to help maintain metabolic health, including those with time-limitations such as shift-workers or those with caring responsibilities. This PhD project will test the hypothesis that the time of day that exercise is performed influences glycaemic outcomes across different phases of the menstrual cycle. We will recruit approximately 50 people with regular menstrual cycles who are not using exogenous hormones. We will use cutting-edge wearable technology to measure glucose levels, physical activity, sleep, heart-rate variability. This will include the use of a novel, patented App to record participant outcomes. We will use this app to record the menstrual cycle, food intake, mood and additional sleep outcomes. The student will collaboratively develop these outcomes by completing a placement with our industrial partner. Importantly, we will engage with participants before and during the project to develop and improve these participant outcomes within the novel app. We will embed participant and public involvement by working with a study-specific advisory group to provide feedback on the study design and procedures, hold a public information meeting to explain the study and answer questions. Finally, we will disseminate our findings through a variety of channels, including our menstrual health website (www.ed.ac.uk/hope), media releases, and presentations at community events. This project aims to answer an important question - does glycaemic regulation in response to exercise at different times of day change over the menstrual cycle? This will improve understanding of this fundamental biology in an understudied area with translational benefits for the public. Further, our project will provide crucial development opportunities for our industrial partners to optimise participant interaction with their novel technology.
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