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A new narrative review led by researchers from UCL and Birmingham Children’s Hospital has found that there is a lack of evidence on the effectiveness of continuous glucose monitoring (CGMs) in non-diabetic people (PNLD).

In the study, published in Diabetic medicineThe researchers conclude that there is currently little published evidence on how accurate CGMs are in measuring blood glucose levels in PNLD, nor sufficient evidence on what health benefit or use such information would provide. The researchers also point out that CGMs may have unintended negative health effects in this user group, and are now calling for better regulation.

In recent years, CGMs have helped transform the treatment of type 1 diabetes and are used with good success by people with type 2 diabetes who are on insulin therapy. The devices, originally designed for diabetics, attach to the body and monitor blood sugar levels in real time. They transmit the information to an insulin pump in people with type 1 diabetes, which delivers the right amount of insulin needed to keep blood sugar levels within a certain range.

For diabetics, CGMs are less burdensome and provide real-time trends in glucose changes compared to older testing methods, such as regular finger-prick blood tests.

More recently, however, CGMs are increasingly being marketed to PNLD for non-medical applications, such as health, wellness and lifestyle management, with some companies providing advice on controlling glucose levels or “glucose spikes.”

Lead author and nutritionist Dr Adrian Brown (UCL Division of Medicine) explained the current interest in CGMs: “Several healthcare companies are now using CGMs as part of paid programs designed to give people personalized nutritional information.”

“Some people say you can adjust a person’s diet and activities to keep blood sugar levels at ‘normal’ levels. But what constitutes a normal blood sugar level varies from person to person and for the same person at different times, and CGM accuracy varies from CGM model to CGM model.

“With this in mind, we wanted to see what research had been done on the use of CGMs in people without diabetes.”

In this narrative review, the team from UCL and Birmingham Children’s Hospital searched online databases (PubMed, Medline, Embase and the Cochrane Library) from 1980–2023 for studies examining aspects of the usefulness and performance of CGM in PNLD. They found 25 relevant studies.

The researchers then sought to determine whether and what evidence there is for the effectiveness of CGMs in measuring glucose levels, glucose variability, and elevated glucose levels in PNLD. They also sought to determine the impact of CGM use on eating behavior.

The review concludes that there is a lack of consistent, high-quality evidence to support the use of CGM in PNLD. For example, there is little evidence on how accurate CGMs are in measuring blood glucose levels or detecting changes in PNLD, nor is there sufficient research on the value and usefulness of CGM data obtained in PNLD.

The review also found evidence that CGM use in PNLD may lead to anxiety about normal eating and blood sugar levels. The researchers say this could pose a risk for the development of eating disorders such as orthorexia (an unhealthy obsession with eating “clean” foods).

A previous separate review by the authors, referenced in this article, addressed the regulation of CGM in people with diabetes and found that no specific regulatory guidance was available.

Dr Brown, from the UCL Centre of Obesity Research, said: “While the personalised health programmes offered by commercial providers have some advantages, such as getting people to think about what and how much they eat, the reality is that we don’t have the same data on the health effects of CGM use in non-diabetics.”

“This report examines the concept of ‘abnormal glucose levels,’ the accuracy of CGM data, and the implications for behavior change when CGMs are used by people without diabetes.

“There is currently a lot of doubt about how much guidance these healthcare companies are giving their customers on how to interpret their blood sugar data and what science this guidance is based on. This can lead to the customer interpreting the meaning of the fluctuations in their blood sugar levels themselves, which carries the risk of them misinterpreting the data and unnecessarily avoiding certain foods.”

Co-author John Pemberton, a pediatric diabetes dietitian at Birmingham Children’s Hospital and member of the International Federation of Clinical Chemistry (IFCC) and the Laboratory Medicine Working Group on CGM, said: “CGMs with an accuracy of 20% of true blood glucose levels in at least 95% of cases represent the best performance on the market today and are extremely helpful for people with diabetes in their day-to-day decision-making about their treatment.

“However, regulations for CGMs for people with diabetes are not clear at both the national and international levels, making it difficult to know whether available CGMs achieve this level of accuracy. For this reason, the IFCC CGM group is pushing for an international standard.

“The situation is even more uncertain for people who do not have diabetes. We have little reliable information on whether CGMs achieve the required accuracy in this population.

“Normal glucose levels for people without diabetes are between 3.3 and 7.8 mmol/L, and the most accurate CGMs tend to have a 20% margin of accuracy. This means that the most accurate CGM devices will show levels between 2.6 and 9.4 mmol/L, even when the actual glucose level is within the normal range. Such deviations can lead to unintended stress and potential psychological and behavioral impacts.

“While CGMs show promise for people without diabetes, the accuracy, regulatory standards and psychological impact of false highs and lows are not well understood. Yet CGMs are heavily promoted without mentioning these problems.”