Between small signals, regulatory hurdles, skin color, and battery life, there’s a hell of a lot of ground to cover before a smartwatch can measure blood sugar levels.
Recently, Bloomberg ran a story that set the health tech sphere abuzz. Citing insider knowledge, it claimed Apple had reached a major milestone in noninvasive blood glucose monitoring that could revolutionize diabetes treatment as we know it. But although this technology is buzzworthy, you won’t see it arrive on the Apple Watch — or any consumer-grade wearable — for several years to come.
Like other kinds of emerging health tech, noninvasive blood glucose monitoring has both technical and regulatory hurdles to clear. But even if Big Tech and researchers were to figure out a viable solution tomorrow, experts say the resulting tech likely won’t replace finger prick tests. As it turns out, that may not even be the most realistic or helpful use for the technology in the first place.
Testing without a pinprick
Noninvasive blood glucose monitoring is just as it sounds. It’s measuring blood sugar levels without needing to draw blood, break skin, or cause other types of pain or trauma. There are several reasons why this tech is worth pursuing, but the big one is treating diabetes.
When you have diabetes, your body isn’t able to effectively regulate blood sugar because it either doesn’t make enough insulin (Type 1) or becomes insulin resistant over time (Type 2). To manage their condition, both Type 1 and Type 2 patients have to check their blood sugar levels via typically invasive measures like a finger prick test or a continuous glucose monitor (CGM). Finger prick tests involve lancing your finger with a needle and placing a drop of blood on a test strip. A CGM embeds a sensor underneath the skin, which enables patients to monitor their blood sugar levels in real time, 24 hours a day.
Few people enjoy getting poked with needles for yearly shots, let alone daily glucose checks. So you can understand the appeal of noninvasive monitoring. Patients wouldn’t need to draw blood or attach a sensor to their bodies to know when they should take insulin or monitor the efficiency of other medications. Doctors would be able to remotely monitor patients, and that, in turn, could expand accessibility for patients living in rural areas. Beyond diabetes, the tech could also benefit endurance athletes who have to monitor their carbohydrate intake during long races.
It’s one of those scenarios where everybody wins. The only problem is that research into noninvasive blood glucose monitoring began in 1975, and in 48 years, nobody’s been able to figure out how to reliably do it yet.
The glucose signal in the biological haystack
Right now, there are two main methods of measuring glucose levels noninvasively. The first is measuring glucose from bodily fluids like urine or tears. This is the approach Google took when it tried developing smart contact lenses that could read blood sugar levels before ultimately putting the project on the back burner in 2018. The second method involves spectroscopy. It’s essentially shining light into the body using optical sensors and measuring how the light reflects back to measure a particular metric.
If it sounds familiar, that’s because this tech is already in smartwatches, fitness trackers, and smart rings. It’s how they measure heart rate, blood oxygen levels, and a host of other metrics. The difference is, instead of green or red LEDs, noninvasive blood glucose monitoring would use infrared or near-infrared light. That light would be targeted at interstitial fluid — a substance in the spaces between cells that carries nutrients and waste — or some other vascular tissue. As with heart rate and blood oxygen, the smartwatch would theoretically use a proprietary algorithm to determine your glucose levels based on how much light is reflected back.
But while the method is similar, applying this tech to blood glucose is much more complicated.
“The signal that you get back from glucose happens to be very small, which is unfortunate,” says David Klonoff, medical director at the Diabetes Research Institute at Mills-Peninsula Medical Center in San Mateo, California. Klonoff also serves as president of the Diabetes Technology Society, editor-in-chief of the Journal of Diabetes Science and Technology, and has followed noninvasive glucose monitoring tech for the past 25 years.
When it comes to glucose, it turns out size matters. That small signal makes it difficult to isolate glucose from other similarly structured chemicals in the body. It’s a headache for device makers, who can get tripped up by something as simple and ubiquitous as water.
“Water interferes with measurement in optical methods, and our bodies are filled with water. If you have any subtle changes in amounts of water, that can dramatically affect the signals you’re measuring,” says Movano CEO John Mastrototaro. Movano made waves for developing a women-first smart ring at CES, but the company has also developed a chip that may potentially be able to measure blood pressure and blood glucose using radio frequencies.
Both Klonoff and Mastrototaro also noted that substances within the body aren’t the only things that make isolating the glucose signal difficult. External and environmental factors like stray light, movement, and poor skin contact with the sensor can also throw off noninvasive measurements. Plus, infrared light is essentially a form of heat. It’s invisible to the naked eye, but all objects — including humans — give off some kind of infrared heat. And sensors aren’t always able to tell whether that heat’s coming from your smartwatch or a sweltering summer day.
For example, say you’re living in a future where smartwatches can noninvasively monitor your blood sugar levels. Climate change triggers a massive heatwave, and your HVAC breaks down. The room gets hotter, you get sweaty, and your smartwatch’s sensor could easily mistake that extra heat as your blood sugar rising.
One workaround is to collect more data by using multiple wavelengths of light — as in, adding more sensors that emit different types of infrared light. The more you have, the easier it is to figure out what’s glucose and what’s interference. But stuffing in more sensors comes with its own set of issues. You need a more powerful algorithm to crunch the extra numbers.And if you add too many wavelengths, you risk adding more bulk to a device.
There are sensors small and power efficient enough to fit into a smartwatch, but taking frequent, continuous measurements will still drain the battery. For example, many wearables that support nighttime SpO2 tracking will warn you that it may dramatically lessen battery life once the feature is enabled.
Current CGMs take measurements roughly once every five minutes, so a noninvasive smartwatch monitor would need to at least match that while maintaining at least a full day’s worth of battery. It has to do that plus track activities, power an always-on display, measure a host of other health metrics, fetch texts and notifications, and send data over cellular or Wi-Fi — all this without resorting to adding a bigger battery so the device can be comfortable enough to wear to sleep for truly continuous monitoring.
Another potential issue: optical sensors may not be as accurate for people with darker skin and tattoos. That’s because darker colors don’t reflect light in the same way as lighter colors. Take pulse oximeters, which use red and infrared light to measure blood oxygen. An FDA panel recently called for greater regulation of these devices because they were less accurate for people with darker skin. Noninvasive blood glucose monitors may not have as big of a problem here, as infrared light is better at handling melanin and ink than visible light. But even with that advantage, Mastrototaro says it’s still a challenge with wavelengths currently used in noninvasive glucose monitoring.
Regulatory clearance means adjusting expectations
Despite all of these challenges, technology has evolved to the point where many of these are solvable issues. AI is more powerful, so building algorithms that can handle the complexities of noninvasive glucose monitoring is easier than it used to be. Chips and other components keep getting smaller and more powerful. Companies like Movano are actively exploring alternatives to optical sensors. But technology is only one part of the equation.
There’s also the FDA.
Wellness features, like blood oxygen spot checks or heart rate, don’t require the FDA to weigh in on safety or efficacy because they’re for your own awareness. But the stakes for blood glucose levels are much higher. An incorrect reading or false alarm could lead a Type 1 diabetic to administer the wrong dosage of insulin, which could result in life-threatening consequences. For that reason, any smartwatch touting blood glucose monitoring features would have to go through the FDA.
The rub is obtaining FDA clearance or approval is a laborious process that takes months if you’re lucky and years if you aren’t. Device makers have to conduct rigorous testing and clinical trials for accuracy, safety, and efficacy. As frustrating as this is for companies, this level of rigor is a good thing and protects us, the consumers. But there’s no guarantee that any company — even one with a really good idea — will successfully make it through the process. And for many, that’s not a bet worth taking if the pros don’t significantly outweigh the cons.
This is why it’s extremely unlikely that consumer tech companies will even try to replace established methods like the finger prick test or CGMs, at least not anytime soon. It’s more likely that blood glucose on smartwatches will be for fitness or wellness tracking or, more ambitiously, a screening tool for prediabetes.
It’s essentially the path every wearable maker has followed thus far. When Apple introduced FDA-cleared EKGs on the Apple Watch Series 4, the purpose was to flag irregular heart rate rhythms and suggest you see a doctor to assess your risk of atrial fibrillation. It was never intended to help you manage a condition or inform treatment. Other companies like Fitbit, Samsung, and Garmin do the same for their EKG and AFib detection features.
These kinds of screening features may not sound quite as revolutionary, but they create a win-win scenario for researchers, companies, and consumers alike. In this case, the CDC says 96 million American adults have prediabetes, while Type 2 makes up 90 to 95 percent of diagnosed diabetes cases. It’s cynical, but this population represents a bigger customer base for companies for a lot less risk. Plus, all the data gathered from noninvasive monitoring could lead to new insights for researchers and consumers.
“I think what we’re going to see is that there’ll be subtle patterns that we don’t recognize right now that will alert people that they’re somewhere between normal and diabetes. And I think there are going to be patterns that predict certain types of prediabetes,” says Klonoff.
“It’s not just knowing your glucose that’s important. It’s really understanding everything about your health,” adds Mastrototaro, noting that, if successful with its RF tech, Movano hopes to fold glucose into its platform alongside other health metrics like heart rate, activity, and blood oxygen. That, he says, is more valuable as it creates a more complete picture of a person’s health. It’s also the same approach that Mastrototaro took back at Medtronic, where he worked on the team that made the first FDA-cleared CGM in 1999.
“Basically, the tool of the CGM allowed you to monitor trends in people’s glucose over time, so kind of to get an idea of the big picture. That’s where we started and we weren’t using it for real-time monitoring,” Mastrototaro explains, referring to how a Type 1 diabetic may use CGMs to determine how much insulin to take. “In the labeling of the initial products, it said that you can use this data for trends, you can use it to give you an idea, you can even use it to alert you if it thinks your blood sugar’s going too high or too low, but then you should confirm it with one of the fingerprick tests to verify and then treat.”
Sounds an awful lot like how smartwatches detect irregular heart rate rhythms before advising users to seek an official diagnosis from a doctor.
Get ready to wait
While Big Tech likes to disrupt and break things, medicine does not. It took nearly two decades for CGMs to be deemed accurate enough for use as a primary real-time blood sugar monitor. It’s not unfathomable to think noninvasive measures might take a while, too.
Neither Klonoff nor Mastrototaro felt confident enough to give any predictions as to when we might see noninvasive blood glucose monitoring on a smartwatch you can actually buy.
The milestone Bloomberg referred to was Apple purportedly developing an iPhone-size prototype, dramatically reducing the size of the device that previously had to rest on a table. This is all speculation, but if it were true, Apple has a lot of work left to do. First, Apple would need to shrink down this prototype to fit in the Apple Watch.More data from the smaller prototype would need collecting, before ideally publishing the results in a peer-reviewed journal. Everything would have to be reviewed by the FDA. And this is if everything goes swimmingly, without any setbacks or errors that require the company to go back to the drawing board.
But perhaps Sumbul Desai, Apple’s VP of health, put it best. When asked about the possibility of blood glucose sensors in a future Apple Watch in a recent interview, she merely said, “All of these areas are really important areas but they require a lot of science behind them.”
You can’t, and shouldn’t, rush good science. And we’ve all seen what happens when companies ship a half-baked, rushed product. Personally, I’m willing to wait for someone to get it right.