The Miracle of Continuous Glucose Monitors
When I was diagnosed with type 1 diabetes in 2008, I had to become an expert in what seemed to me at the time a niche and completely random area of medical knowledge: carbohydrate content in food, the hormone insulin, how to inject yourself with it.
Along with administering insulin, I learned to prick my finger four to five times every day, extracting blood to test for sugar. These pricks left marks on the sides of my fingers, which were perpetually swollen and would sometimes hurt to touch. But they were useful: the regular blood tests enabled me to monitor my blood glucose. I would infer its level from a rough combination of the most recent test result, and an interoceptive glance at how my body was feeling. Shaky, unable to think straight? Blood sugar too low. Lethargic and irritable? Probably too high.
I don’t know if this description is arousing envy, but in its geographical and historical context, my situation was incredible. The UK’s National Health Service provided me with all the blood testing equipment I would ever need, free of charge. This was tragically lucky. It is estimated that globally, for every two people living with type 1 diabetes today, a third one has died because they cannot access the medical supplies they need (Fralick et al. 2022). The reasons for this range from government funding and company overpricing, to poor education and inability to access medication during wars or natural disasters.
As well as benefitting from the NHS, I was living in the most modern moment the world had ever seen – and therefore, I could access the most advanced medication ever invented. The original method of monitoring glucose in people with diabetes, as documented across ancient Indian, Persian and Greek texts dating back to at least 5th Century BC, was via the ‘honey-like’ taste of patients’ urine (Eknoyan and Nagy 2005). This would be measured by the attraction of ants and other insects to the urine (Zarshenas, Khademian, and Moein 2014), and any other available methods for establishing taste.
More systematic attempts to quantify urine glucose began in the mid-1800s, and in 1908, a copper reagent for urine glucose testing was invented (Hirsch 2018). Home testing with this method was introduced in 1925. Patients conducted a test mixing the copper reagent, boiling water, and their own urine, and were greeted with a red/yellow/green traffic light system loosely corresponding to glucose level (Olczuk and Priefer 2018). The invention, in 1965, of the first blood glucose test strip, finally heralded the end of the era of urine testing. In 1980, the first self-monitoring blood glucose kit was launched for home use, and these continued to improve across the decades, giving increasingly precise measurements with smaller amounts of blood required (Hirsch 2018).
This, it was thought, was the end of the road for blood sugar monitoring technology. There could be no measurement of blood sugar without extracting new blood from the body each time, as it would never be safe to insert technology into the bloodstream continuously. But then, in 1999, the first continuous glucose monitor was approved by the FDA. CGMs, which currently take the form of small devices which you can stick to your arm, get around the impossibility of continuous blood monitoring, because they do not actually go into the bloodstream. Instead, they are inserted into the interstitial fluid, the solution between cells, and monitor the glucose level there as a delayed proxy for blood sugar. Because of the time lag between glucose level in blood and interstitial fluid, it was believed that CGMs could never replace blood tests. But several years after their invention, it turned out that CGMs have a temporal resolution which is indeed high enough to replace regular blood testing in diabetes care.
The moment when a doctor first informed me about CGMs was one of the few times in my life that I have genuinely cried with happiness. Having thought I’d never live another day without a self-given blood test, I suddenly found out I might never have to do one again. In retrospect, this realisation might not have been so dramatic if I had bothered to keep more up-to-date with emerging technology research – but that was how I experienced it at the time. More importantly than liberating me from the blood testing ritual, CGMs would substantially improve my ability to control my blood sugar level. This gave me unprecedented hope for my long-term health, changing the way I could think about my own future.
Not only can CGMs be life-saving for people with diabetes, but also for those with, or at risk of, other health conditions affecting blood sugar regulation or awareness – such as eating disorders (Juarascio et al. 2022). Beyond their medical applications, CGMs are also revolutionising research, by providing new windows into the metabolism in health and disease. For example, research here at the CBU is using CGMs to investigate the relationship between glucose absorption and cognition (Fleming, Stasiak, and Nord 2023).
But the most well-known application of CGMs today is the one that, had I been told about back in that first doctor’s appointment, I would have found the strangest. Surfing the wave of ‘wellness’ culture, companies like ZOE are now selling CGMs as a tool for people without health conditions to wear and observe their own blood sugar fluctuations. This is despite no convincing scientific evidence, yet, that this is beneficial for their health, and no research into potential risks either[1].
Seeing healthy people wearing a medical device invented to treat a specific health condition, which all over the world people with that health condition can’t access, feels – to be honest – slightly weird. But when I think about it, I guess that maybe this is really just a case of bad optics. The global crisis in access to diabetes medication wasn’t caused by healthy people wearing CGMs, and stopping them from doing so wouldn’t solve it either.
Maybe, instead, the newfound celebrity of the little medical device I have to stick to my arm is more of an opportunity. Commercial CGM companies currently do little to rectify the striking lack of public knowledge about what diabetes actually is – with no mention of CGMs’ original purpose as diabetes medication in their descriptions at all (‘How ZOE Works’, n.d.; ‘How Signos Works - Personalized Weight Loss | Signos’, n.d.; ‘January AI | How It Works’, n.d.).
But what if they did?
Imagine if everyone who learned about CGMs for healthy people, also learned about their role in diabetes: how hard people with diabetes work every day to achieve blood sugar ranges like their own, and what happens to those who can’t access the medication they need. Stepping onto some arguably more unrealistic terrain, imagine, also, if everyone who bought themselves a CGM donated some money to a diabetes charity as well. Soaring CGM sales for people without health conditions could then bring with them greater CGM availability for people with diabetes, and even increased funding for diabetes research.
And you don’t need me to tell you what increased funding for diabetes research could bring. Even more cool stuff for us all to stick on our arms.
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[1]An observational study, with no placebo control, combined CGM with other forms of biofeedback and showed improved health behaviours and so-called ‘time in [glucose] range’ in individuals with no health conditions (Dehghani Zahedani et al. 2021). ‘Time in range’ is a clinical definition which can’t necessarily be directly imported to measure health in people without health conditions. Every researcher running this study was affiliated with JanuaryInc, the company which created the CGM healthcare App being tested. A CGM-selling company Signos, with similar financial incentive to demonstrate the benefits of CGMs, is currently planning the largest ever study to look at the effects of CGMs in healthy people (‘Signos Launches a First-of-Its-Kind 20,000 Person Study on CGM Use Paired With an AI-Powered Health App to Unlock the Role of Glucose Responses in Health Outcomes for All’ 2022). To investigate the benefits of CGMs, we would ideally need to compare CGMs alone with a control group. Such a study should also test for any negative effects of CGM use – such as increased risk of anxiety or eating disorders, and less optimal health behaviours from focusing on the metabolic markers we can observe (e.g. rate of glucose absorption) at the expense of equally important but less visible ones.
References
Dehghani Zahedani, Ashkan, Solmaz Shariat Torbaghan, Salar Rahili, Kirill Karlin, Darrin Scilley, Riya Thakkar, Maziyar Saberi, et al. 2021. ‘Improvement in Glucose Regulation Using a Digital Tracker and Continuous Glucose Monitoring in Healthy Adults and Those with Type 2 Diabetes’. Diabetes Therapy 12 (7): 1871–86. https://doi.org/10.1007/s13300-021-01081-3.
Eknoyan, Garabed, and Judit Nagy. 2005. ‘A History of Diabetes Mellitus or How a Disease of the Kidneys Evolved into a Kidney Disease’. Advances in Chronic Kidney Disease 12 (2): 223–29. https://doi.org/10.1053/j.ackd.2005.01.002.
Fleming, Hugo Alexander, Martyna Stasiak, and Camilla Nord. 2023. ‘Metabolic Reward Signals in Learning and Mental Health’, August. https://doi.org/10.17605/OSF.IO/UQ58Z.
Fralick, Michael, Alicia J. Jenkins, Kamlesh Khunti, Jean Claude Mbanya, Viswanathan Mohan, and Maria Inês Schmidt. 2022. ‘Global Accessibility of Therapeutics for Diabetes Mellitus’. Nature Reviews. Endocrinology 18 (4): 199–204. https://doi.org/10.1038/s41574-021-00621-y.
Hirsch, Irl B. 2018. ‘Introduction: History of Glucose Monitoring’. In Role of Continuous Glucose Monitoring in Diabetes Treatment. Arlington (VA): American Diabetes Association. http://www.ncbi.nlm.nih.gov/books/NBK538968/.
‘How Signos Works - Personalized Weight Loss | Signos’. n.d. Accessed 2 February 2024. https://www.signos.com/how-it-works.
‘How ZOE Works’. n.d. Accessed 20 January 2024. https://zoe.com/how-it-works.
‘January AI | How It Works’. n.d. Accessed 2 February 2024. https://january.ai/how-it-works.
Juarascio, Adrienne S, Paakhi Srivastava, Emily K Presseller, Mandy Lin, Anna G G Patarinski, Stephanie M Manasse, and Evan M Forman. 2022. ‘Using Continuous Glucose Monitoring to Detect and Intervene on Dietary Restriction in Individuals With Binge Eating: The SenseSupport Withdrawal Design Study’. JMIR Formative Research 6 (12): e38479. https://doi.org/10.2196/38479.
Olczuk, David, and Ronny Priefer. 2018. ‘A History of Continuous Glucose Monitors (CGMs) in Self-Monitoring of Diabetes Mellitus’. Diabetes & Metabolic Syndrome: Clinical Research & Reviews 12 (2): 181–87. https://doi.org/10.1016/j.dsx.2017.09.005.
‘Signos Launches a First-of-Its-Kind 20,000 Person Study on CGM Use Paired With an AI-Powered Health App to Unlock the Role of Glucose Responses in Health Outcomes for All’. 2022. 16 February 2022. https://www.businesswire.com/news/home/20220216005221/en/Signos-Launches-a-First-of-its-Kind-20000-Person-Study-on-CGM-Use-Paired-With-an-AI-Powered-Health-App-to-Unlock-the-Role-of-Glucose-Responses-in-Health-Outcomes-for-All.
Zarshenas, Mohammad M., Sedigheh Khademian, and Mahmoodreza Moein. 2014. ‘Diabetes and Related Remedies in Medieval Persian Medicine’. Indian Journal of Endocrinology and Metabolism 18 (2): 142–49. https://doi.org/10.4103/2230-8210.129103.
