HbA1cmmol/mol
3-month average glucose exposure
Also known as: Haemoglobin A1c, Glycated Haemoglobin
Typical optimal range
20–42 mmol/mol
A result in roughly the 20–42 mmol/mol range is generally considered optimal, though exact reference intervals differ between laboratories, so always read your result alongside the range your own lab provides. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Diagnosis and management of type 2 diabetes in the UK follow NICE guideline NG28 (Type 2 diabetes in adults: management) and the associated NICE pathway on diabetes diagnosis, with HbA1c thresholds aligned to WHO 2011 diagnostic criteria as adopted by NHS England.
What is HbA1c?
HbA1c (haemoglobin A1c, or glycated haemoglobin) is formed when glucose in the bloodstream attaches to haemoglobin, the oxygen-carrying protein inside red blood cells. Because red blood cells live for roughly 10–12 weeks, the proportion that has become glycated gives a reliable picture of average blood glucose levels over the past two to three months. This makes it considerably more informative than a single fasting glucose reading, which can vary day to day, and it is the principal test used by GPs and diabetes teams in the UK to screen for, diagnose, and monitor type 2 diabetes.
What a high HbA1c means
A result above the optimal range is a signal that average glucose levels have been running higher than ideal — something worth exploring further with a GP rather than an immediate cause for alarm. Levels in the 42–47 mmol/mol range are used clinically to identify a 'pre-diabetes' picture, while a reading of 48 mmol/mol or above on repeat testing meets the diagnostic threshold for type 2 diabetes under NICE guidance.
- Excess refined carbohydrate and sugar intake. Diets high in rapidly digested carbohydrates and added sugars cause repeated spikes in blood glucose, which over time raise the glycated fraction of haemoglobin. This is one of the most modifiable contributors to a rising HbA1c.
- Physical inactivity and excess body weight. Skeletal muscle is the primary site where glucose is cleared from the blood after meals; insufficient movement reduces this capacity. Excess body weight, particularly around the abdomen, is strongly associated with insulin resistance, which pushes glucose levels higher over time.
- Disrupted sleep and chronic stress. Poor or insufficient sleep (fewer than seven hours) and chronic psychological stress both impair insulin sensitivity and can raise cortisol, which in turn elevates blood glucose. Evidence links habitual short sleep to higher HbA1c independent of diet and weight.
A single raised reading should always be confirmed with a repeat test before clinical decisions are made, as acute illness, steroid medication, and other factors can temporarily affect the result.
What a low HbA1c means
A very low HbA1c is not usually a direct health concern in its own right, but it can occasionally indicate that the result is unreliable rather than reflecting genuinely low glucose exposure.
- Haemolysis or blood loss. Conditions that shorten the lifespan of red blood cells — such as haemolytic anaemia or recent significant blood loss — mean fewer older, more glycated cells are present, artificially lowering the measured HbA1c.
- Haemoglobin variants. Certain inherited haemoglobin variants (for example, sickle-cell trait or some thalassaemia traits) can interfere with standard HbA1c assays, producing falsely low or otherwise unreliable readings; alternative glucose monitoring methods may be needed.
If your HbA1c seems unexpectedly low and you have a known haemoglobin variant or blood disorder, flag this to your GP so they can interpret the result in context.
Should I be worried?
A single HbA1c reading outside the optimal range is useful information, not a verdict — it prompts a closer look rather than immediate concern. If your result is in the pre-diabetes range, NICE recommends a repeat test and a structured prevention conversation with your GP, since this stage is often reversible with lifestyle changes. If it meets the diabetes threshold, a confirmatory repeat is standard practice before a diagnosis is made (unless you have clear symptoms). Your GP may look at this result alongside fasting glucose, weight, blood pressure, kidney function (eGFR and urine albumin-to-creatinine ratio), and lipids to build a fuller picture of cardiometabolic risk. Bring any relevant context — recent illness, new medication, family history — to your appointment, as these can all affect interpretation.
What actually helps
Several well-evidenced lifestyle changes can meaningfully lower HbA1c, and even modest improvements in the pre-diabetes range can reduce the risk of progressing to type 2 diabetes.
- Reduce refined carbohydrates and added sugar. Replacing white bread, sugary drinks, and ultra-processed snacks with wholegrains, legumes, and fibre-rich vegetables blunts post-meal glucose spikes and consistently lowers HbA1c in clinical trials. You do not need to eliminate carbohydrates — quality and fibre content matter more than quantity alone.
- Regular aerobic and resistance exercise. Both 'zone 2' aerobic activity (brisk walking, cycling, swimming at a conversational pace) and resistance training improve insulin sensitivity and increase the muscle mass available to absorb glucose. Aim for at least 150 minutes of moderate activity per week in line with NHS physical activity guidelines, ideally spread across most days.
- Prioritise seven to nine hours of sleep. Consistent, good-quality sleep supports healthy cortisol rhythms and insulin sensitivity. Even a few nights of poor sleep can measurably blunt glucose regulation, so treating sleep as a health behaviour — not a luxury — is worth taking seriously.
- Achieve and maintain a healthy weight. Losing as little as 5–10% of body weight in people who are overweight has been shown in large trials, including the NHS Diabetes Prevention Programme evidence base, to produce clinically meaningful reductions in HbA1c.
There is good supporting evidence for the following foods and dietary patterns in managing blood glucose and HbA1c.
Non-starchy vegetables
High in fibre and low in rapidly digestible carbohydrate, they bulk out meals without raising blood glucose significantly and support a healthy gut microbiome linked to better metabolic health.
Legumes (lentils, chickpeas, beans)
Legumes have a low glycaemic index and are rich in soluble fibre, which slows glucose absorption; regular consumption is associated with lower HbA1c in systematic reviews.
Wholegrains (oats, barley, wholegrain bread and pasta)
Compared with refined grains, wholegrains produce a slower, lower glucose response; oats and barley in particular contain beta-glucan, a soluble fibre with robust evidence for blunting post-meal glucose rises.
Oily fish (salmon, mackerel, sardines)
While not directly lowering HbA1c, oily fish provides omega-3 fatty acids that support cardiovascular health — important given the elevated CVD risk that accompanies raised HbA1c — and replaces higher glycaemic foods when eaten as a protein source.
Nuts and seeds
Rich in unsaturated fats, fibre, and protein, nuts have a low glycaemic impact and replacing refined snacks with a small daily portion is linked to modestly improved glycaemic markers in meta-analyses.
Berries
Lower in sugar than many other fruits and high in polyphenols, berries have a relatively modest effect on blood glucose and there is emerging evidence that their anthocyanins may improve insulin sensitivity, though research is ongoing.
Track your own HbA1c
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Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.