HbA1c: The Single Number That Tells You How Your Metabolism Is Doing

If we could pick one biomarker for adults over 40 to know — to actually know, with their own number, tracked over time — it would be HbA1c. It's cheap, it's universally available, it's deeply informative about metabolic trajectory, and it's badly under-utilised by both clinicians and patients.

What HbA1c actually measures

HbA1c is glycated haemoglobin — haemoglobin (the oxygen-carrying protein in red blood cells) that's had glucose stuck to it. The reaction is non-enzymatic and irreversible: glucose binds, and the bound state persists for the lifetime of that red blood cell (around 90-120 days).

Because red blood cells are constantly being replaced, the HbA1c percentage you measure today reflects the average blood glucose over the previous 8-12 weeks. It's a time-integrated measure — much more informative than a single fasting glucose reading, which is just a snapshot.

The number is reported either as a percentage (the older convention) or as mmol/mol (the IFCC standard, now used in most U.S. labs). Both forms are equivalent — a 5.6% reads as 38 mmol/mol; a 6.5% reads as 48 mmol/mol.

The categories that matter

The clinical thresholds for HbA1c are:

• Below 5.6% (38 mmol/mol): healthy non-diabetic range.
• 5.7–6.4% (39–47 mmol/mol): pre-diabetic. Insulin resistance is established.
• 6.5%+ (48+ mmol/mol): diabetic.

But these thresholds are clinical cutoffs, not optimal targets. The relevant question for most adults isn't "am I diabetic?" but "where am I on the glide path, and what direction am I moving?"

Optimal targets vs. clinical thresholds

Healthy young adults typically have HbA1c around 4.8-5.2%. Most middle-aged adults sit somewhere between 5.3 and 5.5%, which is "fine" by clinical standards but materially worse than their twenties self.

For adults over 40 thinking about long-term metabolic health, reasonable optimal targets:

• 5.0–5.3%: excellent for adults over 40. Comparable to a metabolically-healthy younger person.
• 5.4–5.6%: healthy but room for improvement, particularly if trending up.
• 5.7%+: insulin resistance is established. Time to act, regardless of whether you've crossed the formal pre-diabetic threshold.

The goal isn't perfection. The goal is "stable or trending down" rather than "drifting up year after year."

How often to check

For adults over 40 with no specific concerns:

• Annually — minimum, included in most general health checks.
• Every 3-6 months — if your last result was 5.5%+ and you're working on lifestyle changes.
• Every 3 months — if you're in the pre-diabetic range and actively intervening, or if you're using interventions like Grenov and want to track effect.

The 3-month interval matches the biological lifetime of red blood cells, so it's the shortest meaningful re-check period.

The companion measurements

HbA1c alone is informative but not complete. The companion measurements that round out the picture:

• Fasting glucose — single-point measure, useful for checking that morning glucose is well-controlled.
• Fasting insulin — the most under-ordered, most informative marker. Catches insulin resistance years before HbA1c moves.
• HOMA-IR — calculated from glucose and insulin, gives a clearer picture of insulin sensitivity.
• Triglyceride-to-HDL ratio — a cheap proxy.

Most GPs will run HbA1c and fasting glucose without much pushing. Fasting insulin sometimes requires asking for it specifically. The full panel is worth requesting at least every 1-2 years.

What moves HbA1c

The interventions, in order of typical impact:

1. Body composition. Losing 5-10kg of visceral fat moves HbA1c by 0.3-0.7% in most adults.
2. Strength training. Building muscle improves glucose disposal capacity, gradually but reliably.
3. Carbohydrate quality and timing. Reducing refined carbs and clustering whole-food carbs around training improves the post-meal glucose pattern that contributes to HbA1c.
4. Sleep. Chronic sleep deprivation is independently insulin-resistance-promoting. Sleep deprivation can raise HbA1c by 0.2-0.4% on its own.
5. Targeted supplementation. Berberine + cinnamon + chromium can produce HbA1c reductions of 0.3-0.7% over 12 weeks in pre-diabetic populations. This is Grenov's territory.

The honest summary

HbA1c is one of those rare biomarkers that's genuinely informative, easy to measure, cheap, and almost universally available — yet badly under-tracked in adults outside formal diabetic care. Knowing your number, knowing the direction, and knowing what moves it puts you in a different category of metabolic awareness.

Get the test. Track the trend. The numbers are yours.