HbA1c

Oct 2

6 min read

Updated: Oct 5

The single blood test that reveals months of your metabolic story — and what it quietly misses

For busy people, or to tune in when on the move, a Google NotebookLM audio podcast is available as a story beneath.

The Test Everyone Has Heard of and Almost Nobody Fully Understands

Picture a red blood cell as a tiny delivery van travelling through your bloodstream. It has a lifespan of roughly 90 to 120 days before it is retired and replaced. During its working life, glucose in the blood sticks to the haemoglobin — the protein inside the van that carries oxygen — in a process called glycation. The more glucose floating around in the blood over those months, the more haemoglobin gets coated. HbA1c measures the percentage of haemoglobin that has been glycated. It is, in effect, a three-month average of your blood sugar levels, baked into the very cells circulating in your veins.

This is why doctors love it. Unlike a standard fasting glucose test, which is a single photograph of one moment, HbA1c is more like a time-lapse video of your glucose landscape over an entire season. And crucially, it does not require fasting — a genuine clinical advantage, since fasting tests are frequently done incorrectly.

The WHO and clinical bodies in both the UK and USA use the same test and the same threshold for diabetes, expressed in two units. The UK prefers mmol/mol; the USA almost always reports a percentage. They measure the same thing — just in different languages. Normal is below 42 mmol/mol (6.0%) in the UK and below 39 mmol/mol (5.7%) in the USA. Non-diabetic hyperglycaemia — what the USA still calls pre-diabetes — runs from 42 to 47 mmol/mol (6.0% to 6.4%) in the UK and 39 to 47 mmol/mol (5.7% to 6.4%) in the USA. Diabetes is 48 mmol/mol or above, or 6.5% and above, in both countries.

What matters is not just where your number sits today, but which direction it is heading. A result of 40 mmol/mol (5.8%) that was 35 mmol/mol (5.3%) five years ago deserves your full attention — even though both would be reported as normal in the UK.

Why a Normal HbA1c Does Not Mean Your Glucose Is Behaving Itself

Because HbA1c is an average, it hides peaks and troughs. Imagine two people with identical results. One has a gently undulating glucose profile. The other spends the day lurching from spikes after every meal to hypoglycaemic dips in between, with the highs and lows averaging out to the same number. On paper, they look identical. Metabolically, they are living in very different bodies.

Those post-meal spikes — postprandial glucose excursions — drive oxidative stress, activate inflammatory pathways, and damage arterial walls over time. A normal HbA1c can sit comfortably on a results printout while these spikes are quietly doing harm.

There is also the question of insulin resistance. In its early stages, the pancreas simply produces more insulin to compensate, and blood glucose stays normal. HbA1c will look perfectly fine. The insulin resistance, however, is already there — already driving visceral fat accumulation, already nudging blood pressure upward, already beginning to alter lipid metabolism. HbA1c cannot see any of this.

This is why, within the VAT Trap framework — which tracks four interconnected pillars of cardiometabolic risk — HbA1c sits within the third pillar as a useful but incomplete picture. It needs to be viewed alongside fasting insulin, waist measurement, and ideally continuous glucose monitoring (CGM) data to give you the full story.

Two further caveats are worth knowing. Very low HbA1c values — below around 30 mmol/mol (4.9%) in people not on glucose-lowering medication — are associated with higher mortality in population studies, often signalling malnutrition or serious underlying illness rather than excellent health. And some people have genetic variants, or conditions such as iron-deficiency anaemia or haemoglobin variants common in African, Caribbean, and South Asian populations, that skew the result independently of their actual glucose. This is precisely why HbA1c is most reliably used as a trend in a single individual over time, rather than as a fixed absolute threshold applied identically to everyone.

Turning a Number into a Plan

HbA1c is one of the most responsive biomarkers in all of metabolic medicine. Diet and exercise can move it meaningfully within weeks to months.

Get your baseline. In the UK, your GP will typically check HbA1c annually if you have risk factors — obesity, family history of diabetes, hypertension, or polycystic ovary syndrome. If you are not being offered this, ask for it. In the USA, it should be included in your annual wellness visit panel. Home finger-prick test kits, sent to a certified laboratory, are available in both countries as a practical way to track between appointments.

Stop treating your HbA1c as a pass-or-fail score and start treating it as a trend line. Ask your doctor for your last two or three results and plot the direction. A creeping result — even within the normal range — is a signal to act now.

If you want to understand what your glucose is actually doing between meals and overnight, consider a consumer CGM device, now widely available without a prescription in both the UK and USA. Used as a biofeedback tool, CGM can be transformative — many people are genuinely shocked to discover that their "healthy" breakfast sends their glucose soaring, while a walk after dinner keeps it remarkably flat.

When it comes to reducing a raised HbA1c, the levers are within your control. Reducing refined carbohydrate and ultra-processed food intake is the single most powerful dietary intervention. Increasing resistance exercise builds metabolically active muscle — essentially a glucose sponge, absorbing blood sugar without requiring insulin. Visceral fat reduction consistently drives HbA1c downward, often dramatically.

The VAT Trap Connection

HbA1c is the downstream readout of a process that begins long before glucose rises — and at the centre of that process is visceral adipose tissue, the metabolically active fat stored deep within the abdomen around the organs.

Visceral fat releases a continuous stream of inflammatory molecules and free fatty acids that directly impair insulin signalling in muscle, liver, and fat tissue. As insulin resistance deepens, the pancreas compensates by producing more insulin. Glucose levels hold steady and HbA1c looks normal, while the underlying metabolic machinery is already faltering. Eventually, when the pancreas can no longer keep pace, glucose rises and HbA1c follows.

Reducing visceral fat — the fourth pillar of the VAT Trap framework — is therefore not simply about waist size or appearance. It is about interrupting the causal chain that drives glucose dysregulation before the HbA1c tells you something has already gone wrong. A rising HbA1c, even within the normal range, is visceral fat making its presence known in the language of glucose chemistry. Listening early is everything.

Key Takeaways

1. HbA1c measures the average amount of glucose that has stuck to red blood cells over roughly three months, making it a reliable trend marker but one that cannot show dangerous daily spikes or early insulin resistance.

2. A normal HbA1c does not mean your glucose metabolism is healthy — insulin resistance and significant post-meal glucose surges can both be present while the three-month average looks reassuring.

3. HbA1c is most powerfully used as a personal trend over time rather than a single pass-or-fail threshold, because individual genetic and dietary factors mean the absolute number varies between people in ways that matter clinically.

4. A raised HbA1c can be brought down significantly through targeted reduction in refined carbohydrates, regular resistance exercise, and visceral fat loss — and continuous glucose monitoring can act as a real-time biofeedback tool to guide those changes.

Summary

SUMMARY

HbA1c is one of medicine's most widely used blood tests, yet most people misunderstand what it actually measures. This article explains how the test works, why a normal result isn't the same as a clean bill of health, and how to use it to track your metabolic future.

VAT Trap