Is blood sugar monitoring without diabetes worthwhile?

Here's an ad you haven't seen, but it could be coming soon: A man jogs along a dirt path meandering through idyllic countryside. He pauses at an overlook and glances down at his cellphone. The phone screen flashes a number, telling him his blood sugar is normal. He smiles and resumes his run.

What's different about this ad, you wonder? The jogger doesn't have diabetes. So, how does his phone know his blood sugar? And why, in the middle of a run, does he want to know the result? Read on.

If you don't have diabetes, should you monitor your blood sugar?

Several companies are working hard to make this sort of ad a reality, as they begin marketing implantable blood sugar measuring devices to people without diabetes. Called continuous glucose monitoring systems, or CGMs, they are often used by people with diabetes. These companies could reap enormous profits by convincing healthy people without diabetes (or other blood sugar problems) to start monitoring blood sugar.

CGMs use tiny sensor wires, or filaments, that pierce the skin to frequently and easily assess blood sugar levels. The filaments remain in place, usually on the upper arm or abdomen, protected by an adhesive patch. Results are displayed on a receiver or transmitted to the user's phone.

While CGMs have required a prescription in the past, recent FDA clearance of over-the-counter CGMs may tempt healthy people to begin using these systems without a specific medical reason to do so.

Where's the health benefit in this?

Already, many of us monitor our weight, heart rate, or steps per day — so why not monitor blood sugar? And, is there any evidence of benefit for healthy people without diabetes to continuously monitor their blood sugar levels with CGMs? There's little published research to help answer these questions.

The best study I could find found nothing particularly surprising: among 153 people who didn't have diabetes, about 96% of the time blood sugar levels were normal or nearly so. In fact, many of the abnormal levels were considered implausible or a mistake. Another small study looked at sedentary individuals without diabetes who were overweight or obese. Participants completed a counseling session about the effects of physical activity on blood sugar and used a CGM device and an activity tracker for 10 days. Afterward, they reported feeling more motivated to exercise. Yet another analysis of CGM use for rare conditions causing low blood sugar among children found no evidence of health benefit.

But I could find no published study suggesting that monitoring translates into improved health for healthy people without diabetes or other blood sugar problems.

So, until more studies prove the value of CGM for people without diabetes, we won't know whether the cost and time it takes to implant one of these systems is accomplishing anything or is just the latest health monitoring fad wasting effort and money.

Speaking of cost, CGMs aren't cheap: they can cost several thousand dollars a year. And it's unlikely that health insurers will cover CGMs for people without diabetes, at least until there is compelling evidence that they're actually helpful.

Blood sugar monitoring for people with diabetes offers undeniable health benefits

For people with diabetes, a major goal of therapy is to keep the blood sugar close to the normal range. This helps to prevent symptoms and complications, prolong life, and improve quality of life.

The development of CGM devices that can frequently and easily monitor blood sugar levels without finger sticks has revolutionized care for millions of people with diabetes. Besides providing results of blood sugar levels, some devices have alarm settings that alert the user, or other people, if blood sugar becomes dangerously low or high. And some systems can transmit results directly to the user's doctor, if desired.

If knowledge is power, why not monitor your blood sugar?

So, why would a person who doesn't have diabetes want to monitor their blood sugar? Possible reasons include

• Detecting prediabetes. In prediabetes blood sugar is slightly high, but not high enough to meet the definition of diabetes. For healthy people, blood sugar testing is typically recommended every three years or so; if prediabetes is diagnosed, repeat testing is recommended more often, at least yearly. CGM might allow earlier diagnosis of prediabetes or diabetes. This could be particularly helpful for people at higher risk for diabetes due to family history or other factors, and people taking medicines that can raise blood sugar.
• The notion of "optimizing" blood sugar for peak mental or physical performance. Not surprisingly, some CGM makers suggest knowing your blood sugar can help you make changes to keep it in an "ideal range" that will help you perform your best, prevent diabetes, or improve health in some other way. For example, you might change what or when you eat. None of these marketing notions has been proven, or even well studied. And guess what — even the ideal blood sugar range for a person who isn't diabetic is uncertain.
• A sense of control. Having more information about your body may provide you with a feeling of control over your health, even if you take no immediate action.
• Curiosity. Let's face it, it's tempting to gather information about our bodies that might be interesting (even when we're not sure what to do with it).

But truly, knowledge that is useless, redundant, or inaccurate doesn't make you powerful! It may even be harmful. For example, if biologically insignificant drops in blood sugar lead you to snack more ("to avoid hypoglycemia"), you could gain weight and actually increase your risk of developing diabetes. If the monitoring system sometimes provides inaccurate information or false alarms, unnecessary anxiety, calls or visits to the doctor, visits to an emergency room, and even inappropriate treatment may follow.

The bottom line

Unfortunately, some makers of CGM systems aren't waiting for solid research results to market these devices to healthy people. So, consumers and marketing professionals — not researchers or doctors — may wind up driving demand for the product.

For any new technology there's a scientific learning curve to figure out when to use it. In my view, we're at the very beginning of the learning curve for home monitoring of blood sugar in people without diabetes. Before buying into what may be the next fad in health monitoring, I think we need to learn a lot more.

There is wisdom in the teachings of one of my favorite professors in medical school: "Just because you can measure something doesn't mean you should."

Follow me on Twitter @RobShmerling