Why Your Sleep Tracker Doesn't Know Why You're Awake
- Greg Veek
- 3 days ago
- 2 min read
Professor Ben Bikman in his recent linkedIn post made a point worth sitting with: if you go to bed hyperglycaemic, you're activating your sympathetic nervous system — raising heart rate, blood pressure, and body temperature. All of which will disrupt your sleep. The fix, as he puts it, is straightforward: skip the late snack, and if you must eat, stick to protein and fat.
It's an excellent clinical insight. But it raises a question for anyone who wears a sleep tracker: how would you actually know if this is your problem?
Most wearables — rings, bands, watches — measure the output. Time in deep sleep, HRV, resting heart rate, sleep stages. They tell you the quality of what happened. What they can't tell you is the metabolic state you walked into bed with.
That's where continuous glucose monitoring changes the conversation entirely. A CGM running overnight doesn't just show you your fasting glucose in the morning — it shows you the full curve. Whether you had a late spike that hadn't resolved by midnight. Whether the pattern shifts when you eat earlier, or eat differently.
But here's the other side of the same coin: it's not only hyperglycaemia that disrupts sleep. A hypoglycaemic dip in the early hours triggers a cortisol response — your body's way of raising blood sugar back up. That cortisol spike will pull you out of deep sleep just as effectively, and often at a predictably similar hour each night. If you've ever woken at 2 or 3am feeling wired for no obvious reason, this mechanism is worth knowing about.
Which means the CGM alone doesn't close the investigation — it opens it further. To truly understand what's driving disrupted sleep, you may need to look beyond glucose: cortisol patterns, HRV trends, body temperature data, room temperature at night, and even hormonal markers. Different questions require different tools.
Sleep tracking and glucose tracking are both incomplete on their own. Together, they start to build a picture that's actually actionable. But the most important step, if sleep is genuinely a problem for you, is to work with a holistic practitioner who can look at more than one variable at a time — and help you decide which combination of tools and methods is worth pursuing in your specific case.
Wearables have made us much better at observing ourselves. The next step is learning to use them in combination — and having someone in your corner who knows how to interpret what they're telling you.
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