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Apple has reached a key milestone in its long-running ambition for the Apple Watch to be able to monitor blood glucose levels without the need to prick the skin for a blood sample, according to a report. 

Bloomberg's Mark Gurman reports the secret project hit "major milestones" recently that make the company confident it could market the feature within the Apple Watch. 

Also:How to set up an Apple Watch

Diabetes was the eighth leading cause of death in the US in 2020, and about one in 10 US adults have diabetes, according to the US Centers for Disease Control and Prevention (CDC). 

The incidence of diagnosed type 1 (where the body can't make insulin) and type 2 diabetes (where the body doesn't use insulin well) declined between 2000 and 2019 across all age groups. However, a recent CDC-funded study found incidence of type 2 among young people has "substantially increased", CNN recently reported. It's for type 2 diabetes that the Apple Watch feature could be useful as a preventative measure.     

Rather than pricking the skin, Apple's approach would use "silicon photonics" and "optical absorption spectroscopy" to measure glucose levels in blood. 

Also: How to unpair and pair and your Apple Watch

Apple was granted a US patent for an integrated silicon photonics device in 2021, Patently Apple reported at the time. Apple had funded R&D efforts into the technology at UK Rockley Photonics to the tune of$70 million in 2021. However, Apple ended the partnership last year. 

In its place, Apple selected existing semiconductor contract fab partner Taiwan Semiconductor Manufacturing Co. (TSMC) to build the main chip to power the feature.     

Bloomberg reports the glucose-reading effort is being headed up by a previously unreported group within Apple called Exploratory Design Group.

Apple is at the proof-of-concept stage with the project, but needs to miniaturize the technology to a more practical size, Bloomberg reports. The current prototype is about the size of an iPhone and can be strapped to a person's bicep. 

Also: The best green phones: Sustainable and eco-friendly smartphones

One aim is for the Apple system to be a preventative tool that could help people change lifestyles to avoid type 2 diabetes. It would be a significant addition to the Apple Watch's current health capabilities, which include a heart-rate sensor, electrocardiograms (ECGs), body temperature sensing, and calculating blood oxygen levels.  

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