Since it was recently Diabetes Awareness Month in Canada (November) and I had the opportunity to try a Continuous Glucose Monitor (CGM) for 10 days I thought I would share my research findings and experiences. CGM's are extremely useful for those with diabetes but what about for people without diabetes? There have been numerous podcasts about using CGM to "hack your health" and spoiler when I dug into the research there isn't a lot to back up these claims.
One of the main issues with conducting research on non-diabetic individuals is the standards for blood glucose for non-diabetics are not yet available. The research is just starting to emerge to set standards for non-diabetics but it's in early stages (1). As a side note this article does not apply to athletes where the research is emerging and applications are unique.
What is a CGM?
A CGM or continuous glucose monitor is a small device that you wear on your body (stomach or back of arms). It has a tiny needle in it which when inserted goes into your cells and blood circulating touches the needle. This sensor takes blood glucose readings every 5 minutes. The CGM sensor connects either to a reader that you purchase or an App on your phone.
If you do a traditional method of measuring blood glucose (poking finger) this reading will be similar but not 100% the same. The finger poke method tests capillary blood and the CGM measures interstitial fluid glucose. Interstitial fluid (the fluid between the cells) glucose takes about 15-20 minutes to catch up to the capillary blood glucose.
How are CGM's used for diabetes?
CGM's can be a lifesaving and life enhancing technology for those with type 1 diabetes and type 2 diabetes especially those on insulin. The sensor can alert the individual of high blood glucose, low blood glucose and if glucose is trending low or high. The sensor's alerts can prevent incidence of hypoglycemia (low blood glucose) and hyperglycemia (high blood glucose) which would be deemed an emergency. It can also make it safter to travel, exercise and reduce stress with hypoglycemia unawareness. (1)
CGM's can also be helpful for individuals with type 2 diabetes to understand the relationship between diet, exercise, stress, sleep and blood glucose. There has been research to support that the use of data from a CGM can change behavior for those with type 2 diabetes. (2)
Why are CGM's being promoted for people without diabetes?
It appears to me after listening to podcasts and reading articles on the topic that the wellness industry influencers and health provider influencers have taken the benefits of a CGM in diabetes and tried to widely apply it to everyone. There are multiple podcast episodes where doctors, coaches, dietitians, and wellness influencers speak about the benefits and health applications of using a CGM. They may use their own experiences as "case studies" or "evidence" to argue for the use of the CGM in the larger population. The utilization of the CGM for health benefit as an idea at first can appear logical. The problem with this theory is that it is not yet supported by research which also means the harms or side effects have also not been fully studied. At this time, the technology is well beyond the research for this product application.
My Experience: I have a good base knowledge of glucose target ranges and how to utilize the data however when my own BG went up and up and up after a meal my reaction was shock and I questioned "is this normal????" I felt some panic because I saw numbers I didn't expect. In order to make sense of my own data I dove into the research and thankfully what I found was reassuring.
What is a "normal' blood glucose?
Blood glucose standards have been set in fasting state, 2 hours after meals and at a random measurement in time. (3)
Blood glucose and A1C levels for diagnosis (3)
Impaired Fasting Glucose | Fasting blood glucose (FBG) levels from 5.6 to 6.9 mmol/L. It should be noted that the World Health Organization and numerous other diabetes organizations define the IFG lower limit at 6.1 mmol/L. |
Impaired Glucose Tolerance | 2-h post prandial levels during 75-g OGTT (specific test) from 7.8 to 11.0 mmol/L. |
Prediabetes | A1C 5.7 to 6.4%. Prediabetes should not be viewed as a clinical entity in its own right, but rather as risk factor for progression to diabetes and cardiovascular disease. No specific fasting or 2 hour post prandial blood glucose target limits. |
Diabetes | A1C over 6.5%, fasting blood glucose over 7.0mmol/L, 2 hour post prandial >11.1mmol/L or random blood glucose over 11.1mmol/L. |
Definitions (3)
Fasting blood glucose = no food/drink other than water for 8 to 12 hours.
75g OGTT = a 75g carbohydrate oral glucose tolerance test and it has a specific format and is completed at laboratory site.
Post prandial = after meals
If we consider these parameters for diagnostics it can give some insight into how to analyze the data on a CGM. There are no data points for "normal" blood glucose between eating and 2 hours after a meal except if BG is over 11.1mmol/L then to consider further investigations for diabetes.
Normal BG expected without diabetes (3):
Fasting (8-12 hours) | <6.1 to 6.9mmol/L |
2 hours after eating | <7.8mmol/L |
Random BG | <11.1mmol/L |
If when you are wearing your CGM right after a meal your blood glucose goes up to 10mmol/L do not stress! You are within the parameters expected as the 2 hours after eating your blood sugar will raise as your body absorbs the sugar from your meal and distributes it to your cells. As long as your BG is <11.1mmol/L during that time it is considered normal.
Percentage error to expect from a CGM: As reported by two CGM companies available in Canada (Dexcom G7 and Lifestyle Libre) they will have a possible error of 8.2-9.2% for adults. (4) Some research has demonstrated the error may be higher up to 20%. Not following insertion instructions can lead to abnormal readings. Things that can alter the accuracy is laying on the sensor (such as overnight), extreme heat or cold (sauna/hot tub/ heating pad/ cold plunge), certain medications (acetaminophen) or supplements (high dose vitamin C).
What does research say about benefits?
Currently the research hasn't caught up to the technology of CGM. There are no research studies currently demonstrating that having a person without diabetes wear a CGM is of benefit to their short or long term health. (1) If you do routine screening for diabetes with your family physician (A1C and fasting or random BG) this will catch any trends of elevated blood glucose above normal range. So that podcast you listened to touting CGM's for health purposes and it's widespread application is interesting but it's opinion not research based.
Could there be harm in using a CGM without diabetes or another metabolic condition affecting BG?
Yes. The potential for harm which has been identified in the research includes the following:
cost is currently not paid by insurance companies outside of specific criteria with diabetes (cost is upwards of $100 - 125 a sensor which lasts 10-14 days)
tape allergy and/ or skin trauma
stress or distress which could be associated with having access to the data
an absence of consensus standards for defining abnormal values leading to misunderstanding of blood glucose levels
an absence of consensus standards for how to respond to abnormal values leaving questions unanswered and little support for those tracking data
CGM system may provide inaccurate readings if it is applied incorrectly or malfunctions, which could potentially lead to inappropriate or dangerous corrective action
More health data isn't always a positive. For an individual with a history of disordered eating, eating disorders or medical trauma using a CGM could have a potential to cause increased stress and negative behavior change. If you do a social media search it doesn't take long to find someone using a CGM and trying to maintain a "level" blood glucose or a level under a certain number (i.e. 7.5mmol/L) for the entire day. These targets are not supported by health research or body physiology. It can lead to restrictive eating or dieting behaviors and obsessing over the blood glucose data available.
Your dietitian can help!
References
https://www.news-medical.net/news/20240627/Evaluating-CGM-accuracy-and-benefits-in-non-diabetic-populations.aspx and https://pmc.ncbi.nlm.nih.gov/articles/PMC10658694/ and https://www.metabolismjournal.com/article/S0026-0495(23)00244-5/fulltext
https://diabetesjournals.org/care/article/40/12/1631/37000/International-Consensus-on-Use-of-Continuous and https://www.health.harvard.edu/blog/is-blood-sugar-monitoring-without-diabetes-worthwhile-202106112473
Taylor PJ, Thompson CH, Brinkworth GD. Effectiveness and acceptability of continuous glucose monitoring for type 2 Diabetes management: a narrative review. J Diabetes Investig. Accepted Author Manuscript online:Â 30 January 2018. doi:10.1111/jdi.12807
https://www.dexcom.com/all-access/dexcom-cgm-explained/g7-overview
Comments