For those interested in the clinical aspects, what gets measured is glucose in the subcutaneous interstitial fluid (ISF). As others have stated, measuring ISF glucose has been around for awhile, but not in the form of a mainstream product for a variety of reasons, including consistency and reliability because ISF glucose levels lag behind blood glucose levels and can vary between different parts of the body. The lag/latency of ISF glucose is due to the time it takes for glucose to travel through capillaries into tissues, so the lag time can vary from 10-20 minutes.
For more, see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769894/ and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2903977/
My opinion:
For more, see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769894/ and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2903977/
My opinion:
- this could be very useful for early detection and management of Type 2 Diabetes (T2D), much less useful for Type 1 Diabetes (T1D);
- The US Centers for Disease Control (CDC) calls T2D an "epidemic" (https://www.cdc.gov/chronicdisease/resources/publications/aag/diabetes.htm) that will eventually affect 100 million Americans, so a watch that could help that population could be very, very popular