Why I don’t want new health sensors in Apple Watch Series 7


Does Apple Watch need more health sensors?
Does Apple Watch need more health sensors?
Photo: Graham Bower/Cult of Mac

Since Apple Watch gets a hardware update like clockwork every fall, it’s a safe bet we’ll see a Series 7 model next month alongside the iPhone 13. There are plenty of rumors about what to expect, including a better display and a new flat-edged design, both of which sound great to me.

But I’m less keen on the prospect that Apple Watch Series 7 might come with additional health sensors. Here’s why.

Apple Watch is like a hospital on your wrist

The original Apple Watch, released in 2015, came with just one health sensor. It measured your heart rate to calculate the calories you burn during the day. But with almost every model since, Cupertino crammed in more health-related sensors.

Series 2 offered an improved heart-rate monitor that could estimate Heart Rate Variability and VOmax. Series 4 added an ECG feature and Series 6 came with a blood-oxygen sensor.

Rumor has it future models will introduce body temperature and blood-glucose sensors. But the wrist might not be the right place to accurately measure these kinds of data.

The wrist is the wrong place for most health sensors

Imagine a wedding photographer who could only take photos of people’s wrists. They wouldn’t get many bookings. And yet that’s arguably what Apple Watch does. It only has sensors on your wrist, which is at the periphery of your body, far from where most of the interesting stuff happens.

The wrist is a good spot to measure your pulse, but not much else. Take V02 max, for example (or, as Apple calls it, Cardio Fitness). This is a measurement of the oxygen you use while exercising. To monitor it properly you need to wear a face mask that measures the volume of oxygen going in and out of your lungs.

When doctors take an ECG reading, they attach 10 sensors to different parts of the patient’s body. Not just the wrists, but the legs and around the chest as well.

Even Apple’s original fitness device, Nike+iPod, put a sensor in your shoe, which is a better place to track your step count and Mobility Metrics.

Of course, I realize it’s not practical for a consumer device like Apple Watch to have sensors in all these place, but that’s precisely my point. Since it’s first and foremost a watch, just how far should Apple push it in a medical direction?

Most of the interesting stuff in your body happens in your core, not on your wrist.
Most of the interesting stuff in your body happens in your core, not on your wrist.
Photo illustration: Graham Bower/Cult of Mac

How accurate are Apple Watch’s sensors?

Some of the medical data Apple Watch collects isn’t very accurate, according to a study conducted in 2017. While it ranked the best of six wearables evaluated, it still had an error rate above 20% when estimating energy expenditure (which Apple calls Active Energy). The study concluded that
“most wrist-worn devices adequately measure heart rate in laboratory-based activities, but poorly estimate Energy Expenditure, suggesting caution in the use of Energy Expenditure measurements as part of health improvement programs.”

That result doesn’t surprise me. Personally, I’ve encountered several problems with Apple Watch accuracy over the years:

  • When I reset or replace my watch I get significantly different VO2max readings.
  • I occasionally get a High Heart Rate warning when my pulse is normal.
  • Mobility Metrics sometimes tell my I’m limping severely when I’m walking normally.
  • Distance estimates for my daily run vary even though I always take the same route.
  • Every time I use my manual coffee grinder, my watch thinks I’m doing an elliptical workout.

Most of these inaccuracies are fairly minor and don’t really matter when it’s all just a bit of fun for fitness motivation. But that level of precision won’t cut it when you’re using medical data to make life-and-death decisions.

Would you trust your Apple Watch with life-and-death decisions?

It’s an open secret that Apple has been working on a noninvasive blood-glucose monitor for years. CEO Tim Cook was seen trying one out four years ago.

Most people with diabetes need to test their blood-glucose levels regularly to determine how much insulin they require. Traditional blood-glucose meters use a drop of blood for this analysis, while continuous glucose monitors use a disposable sensor placed under the skin.

If Apple Watch could continuously monitor your blood-glucose level without breaking the skin, and display the results in a complication on the watch face, it could be a breakthrough product for people with diabetes. But the readings would need to be highly accurate. The wrong insulin dose could result in high or low blood glucose, which can lead to discomfort, disease or in some cases even death.

Right now, it seems sufficiently accurate technology remains a few years away. Mike Hoskins from Healthline says to date, noninvasive blood-glucose monitoring has “all been hype versus hope,” and speculates the first products might come to market in 2027.

Blood-glucose monitoring is not just a bit of fun like Activity Rings. I hope Apple doesn’t rush this feature. The company should wait to release it when it’s good and ready. I definitely don’t want to see blood-glucose monitoring that isn’t accurate enough to help people with diabetes and is instead used to sell expensive and unnecessary diet apps to people who don’t need to worry about their blood-glucose levels anyway.

Cool wrist, bro

Body temperature is another vital sign used to monitor all manner of different diseases. It’s normally taken with a thermometer in your mouth, up your bum or, in the case of small children, under the arm. There are also more convenient but slightly less accurate ways to measure it in your ear or against your forehead.

Apple Watch is rumored to be getting a skin temperature sensor, too. The trouble is, skin temperature is not the same as internal body temperature. And your wrist is not a great place to take your temperature anyway, as you’ll know if you’ve ever suffered from cold hands. One of the ways your body regulates its temperature is by reducing circulations to extremities, so your wrists can sometimes be significantly cooler than your core.

You can make adjustments for this. For example, readings from the mouth and under the arm are about 0.5 degrees to 1 degrees Fahrenheit lower than rectal temperatures. However, the relationship between wrist and core temperatures is less consistent.

I can’t help wondering just how useful wrist skin temperature would actually be. If I had a fever, I’d prefer to use a traditional thermometer in the mouth.

More medical data doesn’t always result in better health outcomes

Even supposing Cupertino finds ways to solve all these problems, more medical data doesn’t always result in better health outcomes.

Looking for medical problems that haven’t yet been diagnosed is known as screening. It’s tempting to believe that more screening is always a good thing. For example, if we screen more people for cancer, we’ll detect it sooner and save more lives, right?

In reality, it’s a bit more complicated than that. No screening process is perfect. You get “false positives” where someone is diagnosed with a disease they don’t actually have. For example, you might discover a lump that turns out to be benign. This can result in unnecessary and potentially harmful medical procedures.

That’s why when health authorities evaluate the benefits of mass screening programs for diseases like cancer, they conduct clinical trials to make sure they’re not doing more harm than good.

So, while the idea of wearing something on your wrist that is constantly checking for medical problems you’re not yet aware of might seem like a great idea, it actually might not be. It could result in overdiagnosis, unnecessary medical procedures and increased anxiety.

Stress, anxiety and the worried well

I’ll admit it. I’m a bit of a hypochondriac. A couple of years ago, I was sitting on my couch, happily watching Real Housewives, when my wrist started vibrating. My Apple Watch told me my heart rate was abnormally high. But when I checked my pulse manually it turned out to be normal. False alarm.

It happened again a few months later, and this time I decided to turn those notifications off altogether. I decided that, for me, the stress of receiving false positives wasn’t worth the potential benefit that my Apple Watch might in the future detect something serious.

You don’t have to suffer from hypochondria to be worried about your health. Especially these days. While on one level, having an Apple Watch may feel reassuring, all the data and the warnings it generates may be increasing your stress level.

This is known as worried well syndrome: a “person with feared complaint in whom no diagnosis is made.” Giving unnecessary health data to someone who is well but worried could make them feel worse, not better.

Take time to get features right, rather than updating every year

Don’t get me wrong, I love my Apple Watch. Its fitness features are great and the activity stats are good enough for logging my workouts and keeping me motivated.

And I’d welcome more health sensors if they are genuinely useful to people living with diseases like diabetes. I just hope that Apple waits to get these features right, rather than sticking to an annual hardware update schedule. That’s why if Series 7 comes with a new design but no new medical sensors, I won’t be disappointed. These things take time.


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