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Fasting glucose level and dawn effect

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  • Fasting glucose level and dawn effect

    I was measuring approximately 13 hour fasting glucose about 7 am each morning and was concerned that it was around 115 mg/dL. So I got a Freestyle Libre to see what was going on. I'm finding that my average daily glucose is about 85 from the CGM data. It's just that I have a peak around 7-8 am. I wake up about 4 am and the 'dawn effect' begins for about 4 hours. Actually, I can see that glucose starts to rise about 1 hour before I wake up. Cortisol, I guess.

    So, how do you define fasting glucose? 13 hour fasting for me is always high. If I define it to be at 2 pm, then it is probably in the 70s. If I define it to be at 2 am, it is probably in the 80s. It seems that fasting glucose may be pretty meaningless.

    My hbA1C is currently 5.2%.

    I uploaded my 23andme SNP data to and generated
    the circadian rhythm report and I saw this result:

    It shows that SNP rs11605924 on the CRY2 gene is A;A and says:

    This genotype, rs11605924(A;A), has been associated with increased fasting
    glucose levels.

    Cryptochrome circadian regulator 2 (CRY2) is one of the core proteins involved
    in the control circadian system. Physiological processes such as metabolism,
    body temperature and sleep-wake cycles are all regulated by the circadian
    clock. Current research is studying the role of circadian regulating proteins
    such as CRY2 in glucose homeostasis and insulin release.

  • #2
    For most people fasting blood glucose is a 7-10 AM draw, and I think that you are correct in that it is an imprecise marker. I can see how it became the norm given the history of type 1 and then type 2 diabetes diagnosis, and obviously an A1C test is better. Your use of a CGM will provide so much more valuable information, and I think eventual broader use of CGM will help people better equate what they are going to eat to how their blood glucose levels will rise and fall. This ultimately is the goal as it is where high blood glucose levels would become all too obvious to ignore. I can imagine insurance companies paying for CGMs at some point will want feedback from those devices.