Peter Attia's HbA1c target sits considerably lower than standard NHS thresholds, reflecting his proactive, longevity-focused approach to metabolic health. HbA1c — glycated haemoglobin — measures average blood glucose over the preceding two to three months and is central to diabetes diagnosis and management in the UK. While NICE guidelines define 48 mmol/mol (6.5%) as the diabetes threshold, Attia advocates for values in the region of 5.0–5.5% (31–37 mmol/mol) as part of a broader preventive framework. This article explores what that means, how it compares to NHS guidance, and what you can do to optimise your own levels.

What Is HbA1c and Why Does It Matter for Long-Term Health?

HbA1c measures the proportion of glycated haemoglobin in red blood cells, reflecting average blood glucose over the preceding 8–12 weeks and serving as a key marker for diabetes diagnosis and cardiovascular risk assessment.

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HbA1c — glycated haemoglobin — is a blood marker that reflects your average blood glucose levels over the preceding two to three months. When glucose circulates in the bloodstream, it binds irreversibly to haemoglobin within red blood cells. Because red blood cells have a lifespan of approximately 120 days, the proportion of haemoglobin that has become glycated provides a reliable snapshot of longer-term glucose control — typically reflecting the preceding 8–12 weeks, with greater weighting given to more recent weeks — rather than a single-point reading.

HbA1c is expressed either as a percentage (NGSP/DCCT units) or in millimoles per mole (mmol/mol), the latter being the standard used across NHS laboratories in the UK. A result of 48 mmol/mol (6.5%) or above on two separate samples is used to confirm a diagnosis of type 2 diabetes in asymptomatic individuals, whilst values between 42–47 mmol/mol (6.0–6.4%) indicate non-diabetic hyperglycaemia, sometimes referred to as prediabetes. It is important to note that HbA1c is not appropriate for diagnosing gestational diabetes, is unreliable in suspected type 1 diabetes, and should be interpreted with caution in children — in these situations, fasting plasma glucose or an oral glucose tolerance test (OGTT) is preferred.

The clinical importance of HbA1c extends well beyond diabetes diagnosis. In people with prediabetes or diabetes, chronically elevated blood glucose is associated with:

• Increased cardiovascular risk, including coronary artery disease and stroke

• Microvascular complications, such as retinopathy, nephropathy, and peripheral neuropathy

• Cognitive decline over time, based on observational data, though causality within low-normal ranges is not firmly established

Large observational studies — including analyses from the Emerging Risk Factors Collaboration published in The Lancet — suggest a continuous, graded relationship between HbA1c and cardiovascular outcomes, extending into ranges below the diabetes threshold. However, these associations are strongest in the prediabetes and diabetes ranges, and it is important not to overstate the evidence for harm at low-normal HbA1c values in otherwise healthy individuals.

For these reasons, HbA1c has become a central biomarker not only in diabetes management but also in broader preventive medicine. Understanding where your HbA1c sits — and what an optimal target might look like — is increasingly relevant for anyone interested in long-term metabolic health.

Standard HbA1c Targets According to NHS and NICE Guidelines

NICE recommends an HbA1c target of 48 mmol/mol (6.5%) for most people with type 2 diabetes on lifestyle measures or metformin; values below 42 mmol/mol (6.0%) are considered normal in the general population.

In the UK, NICE guidelines provide clear HbA1c targets tailored to clinical context. For individuals with type 2 diabetes managed with lifestyle measures or metformin alone, NICE (NG28) recommends a target of 48 mmol/mol (6.5%). For those on medications that carry a risk of hypoglycaemia — such as sulphonylureas or insulin — the target is slightly relaxed to 53 mmol/mol (7.0%) to reduce the risk of dangerous low blood sugar episodes. Targets should be individualised, particularly in older adults or those with significant comorbidities, where overly aggressive glucose lowering can carry its own risks.

For type 1 diabetes, NICE guidance (NG17) recommends aiming for an HbA1c of 48 mmol/mol (6.5%) or lower if achievable without problematic hypoglycaemia.

For the general population without diabetes, the NHS does not define a specific 'optimal' HbA1c target. The NHS Health Check programme invites all adults aged 40–74 for a cardiovascular risk assessment; HbA1c testing is offered where the risk assessment indicates an increased risk of type 2 diabetes. A result below 42 mmol/mol (6.0%) is generally considered within the normal range.

Where an individual is asymptomatic, NICE and NHS guidance recommend that a diagnosis of type 2 diabetes should be confirmed with a second abnormal HbA1c result on a separate sample, rather than acting on a single test alone. In people with symptoms of hyperglycaemia, a single result is sufficient.

HbA1c should not be used as the sole diagnostic test in certain groups, including:

• People with suspected type 1 diabetes

• Pregnant women (gestational diabetes requires an OGTT)

• Children and young people

• Individuals with conditions that affect red blood cell turnover or haemoglobin structure (see the following section for detail)

It is worth noting that NICE guidance is primarily designed to prevent complications in people already diagnosed with diabetes, rather than to define aspirational targets for metabolic optimisation in otherwise healthy individuals. This distinction is important when comparing conventional clinical thresholds with the more proactive, prevention-focused approach advocated by some clinicians in the longevity medicine space.

Peter Attia's Approach to HbA1c and Metabolic Health

Peter Attia targets an HbA1c of 5.0–5.5% (31–37 mmol/mol), viewing values creeping towards the upper normal range as early metabolic dysfunction warranting lifestyle intervention, alongside fasting insulin and CGM data.

Dr Peter Attia is an American physician and author widely known for his work in longevity medicine, most notably through his book Outlive: The Science and Art of Longevity and his podcast The Drive. Attia advocates for a proactive, data-driven approach to health that prioritises the prevention of chronic disease decades before it manifests clinically — a philosophy he terms 'Medicine 3.0'.

Central to Attia's framework is the concept of metabolic health, which he views as foundational to cardiovascular, cognitive, and overall longevity outcomes. He argues that conventional medicine intervenes too late — typically once disease is already established — and that biomarkers such as HbA1c should be optimised well within the 'normal' range, not simply kept below diagnostic thresholds.

Attia's HbA1c target is generally cited as being in the region of 5.0–5.5% (approximately 31–37 mmol/mol) — considerably lower than the NHS diagnostic cut-off for prediabetes. He emphasises that this should be considered alongside other metabolic markers, including:

• Fasting insulin (as a potential early marker of insulin resistance)

• Fasting glucose

• Triglycerides and HDL cholesterol

• Continuous glucose monitoring (CGM) data, including time in range and glucose variability

Attia's position is that an HbA1c creeping towards the upper end of the 'normal' range — even at 38–41 mmol/mol — may reflect early metabolic dysfunction that warrants attention through lifestyle intervention.

It is important to note that these views represent a preventive, personalised medicine perspective and are not reflected in NHS or NICE clinical guidelines. In particular:

• Fasting insulin and HOMA-IR are not part of NICE-recommended assessments in primary care and lack standardised clinical cut-offs in the UK

• CGM is recommended by NICE for all adults with type 1 diabetes (NG17) and for specific subgroups of people with type 2 diabetes on insulin (NG28), but is not routinely recommended by NICE for people without diabetes

• The evidence base for defining an 'optimal' HbA1c target in non-diabetic populations remains limited and is not established clinical guidance

For people without diabetes who are interested in these markers, fasting insulin testing and CGM use are available on a self-funded basis, but their clinical utility in this context should be discussed with a healthcare professional.

How Attia's Targets Compare to Conventional Clinical Thresholds

Attia's targets reflect individual optimisation rather than population-level disease management; observational data support a graded relationship between HbA1c and cardiovascular risk, but no official guidance recommends targets as low as those he advocates.

The divergence between Attia's aspirational HbA1c targets and those used in standard NHS clinical practice reflects a fundamental difference in philosophy rather than a contradiction of the underlying science. NHS and NICE thresholds are designed as population-level diagnostic and management tools, calibrated to identify disease and reduce complication rates in those already affected. Attia's targets, by contrast, are framed around individual optimisation and the prevention of disease onset.

From an epidemiological standpoint, analyses from the Emerging Risk Factors Collaboration, published in The Lancet, demonstrate a continuous, graded relationship between HbA1c and cardiovascular events across a broad range of values, with no clearly defined lower threshold of benefit. This lends some scientific plausibility to the idea that lower HbA1c — within physiologically reasonable limits — may be associated with better outcomes, though these are observational findings and do not establish causation.

However, several important caveats apply:

Factors that can make HbA1c unreliable:

• Falsely low results may occur in haemolytic anaemia, haemoglobinopathies (e.g., sickle cell trait), or following a blood transfusion

• Falsely high results may occur in iron deficiency anaemia, as reduced red cell turnover leads to older, more glycated cells

• Chronic kidney disease (CKD) and pregnancy can also distort HbA1c values; in these situations, fasting plasma glucose, OGTT, or fructosamine may be more appropriate

Risks of overly aggressive glucose lowering: The ACCORD trial (New England Journal of Medicine, 2008) demonstrated that intensive glucose lowering in older adults with established type 2 diabetes and high cardiovascular risk was associated with increased mortality compared with standard treatment. Whilst this finding is most relevant to people with established diabetes on glucose-lowering medications, it serves as an important reminder that lower is not always better in every clinical context.

There is no official clinical guidance recommending HbA1c targets as low as those Attia advocates for the general population. In summary, Attia's approach is intellectually coherent and grounded in plausible biological reasoning, but it sits outside mainstream NHS clinical practice and should be understood as a personalised preventive framework rather than established medical guidance.

Practical Ways to Optimise Your HbA1c Levels

Reducing refined carbohydrates, increasing dietary fibre, regular aerobic and resistance exercise, and improving sleep quality are the most evidence-based interventions for lowering HbA1c in both diabetic and non-diabetic individuals.

Whether your goal is to meet NHS targets for diabetes management or to pursue a lower HbA1c in the spirit of metabolic optimisation, the foundational interventions are broadly the same and are well-supported by evidence.

Dietary modifications are among the most impactful levers available. NICE (NG28) and Diabetes UK recommend an individualised approach to nutrition, with an emphasis on:

• Reducing intake of refined carbohydrates and added sugars (white bread, sugary drinks, ultra-processed foods) to lower postprandial glucose spikes

• Prioritising dietary fibre from vegetables, legumes, and wholegrains, which supports slower glucose absorption and improved insulin sensitivity

• Lower glycaemic index (GI) carbohydrates as part of a balanced diet

• Weight management, which has a significant impact on insulin sensitivity and HbA1c in people with or at risk of type 2 diabetes

Diabetes UK acknowledges that low-carbohydrate diets can be an effective option for some people with type 2 diabetes or prediabetes, particularly in the short to medium term, but recommends these are undertaken with appropriate support. A Mediterranean-style dietary pattern also has good evidence for improving glycaemic outcomes. Neither approach is universally endorsed by NICE as the single preferred option; the emphasis is on individualisation.

Physical activity is equally important. Both aerobic exercise (such as brisk walking, cycling, or swimming) and resistance training improve insulin sensitivity and glucose uptake into muscle tissue. Short bouts of movement after meals — for example, a 10-minute walk — have been shown in clinical studies (including research published in Diabetes Care) to meaningfully reduce postprandial glucose rises. The UK Chief Medical Officers' Physical Activity Guidelines recommend at least 150 minutes of moderate-intensity activity per week for adults.

Sleep quality and stress management are clinically significant but often overlooked. Poor sleep and chronic psychological stress elevate cortisol, which raises blood glucose and impairs insulin sensitivity. Addressing these factors is a core component of Attia's approach and is supported by a growing body of evidence.

For those interested in deeper insight into their glucose patterns, continuous glucose monitors (CGMs) — such as devices made by Abbott (Libre) or Dexcom — are increasingly accessible to the general public on a self-funded basis without a prescription. However, CGM is not routinely recommended by NICE for people without diabetes, and results should be interpreted in context. NICE recommends CGM for all adults with type 1 diabetes and for specific subgroups of people with type 2 diabetes on insulin.

If you experience any problems with a glucose monitoring device, you can report this to the MHRA via the Yellow Card scheme (yellowcard.mhra.gov.uk).

Any significant dietary or lifestyle changes, particularly in the context of existing medical conditions or glucose-lowering medications (where dietary changes may increase the risk of hypoglycaemia), should be discussed with a GP or registered dietitian.

When to Speak to a GP or Specialist About Your HbA1c Results

Contact your GP promptly if your HbA1c is 48 mmol/mol (6.5%) or above, falls in the prediabetes range of 42–47 mmol/mol, or is rising year on year alongside other metabolic risk factors.

Knowing when to seek professional advice about your HbA1c is an important aspect of responsible self-monitoring. If you have had an HbA1c test — whether through your GP, an NHS Health Check, or a private provider — the following guidance can help you interpret when action is needed.

You should contact your GP promptly if:

• Your HbA1c is 48 mmol/mol (6.5%) or above. In asymptomatic individuals, a second confirmatory HbA1c on a separate sample is recommended before a diagnosis of type 2 diabetes is made. If you have symptoms of hyperglycaemia, a single result is sufficient for diagnosis

• Your result falls in the prediabetes range of 42–47 mmol/mol (6.0–6.4%), as this warrants lifestyle intervention and regular monitoring — your GP can refer you to the NHS Diabetes Prevention Programme (NDPP)

• You have symptoms suggestive of hyperglycaemia, such as increased thirst, frequent urination, unexplained weight loss, or fatigue, regardless of your HbA1c result

• Your HbA1c is rising year on year, even if still within the normal range, particularly if you have other risk factors such as obesity, a family history of type 2 diabetes, or polycystic ovary syndrome (PCOS)

Seek same-day urgent medical attention (same-day GP, urgent care, or 999 if very unwell) if you or someone else has symptoms that may suggest type 1 diabetes or diabetic ketoacidosis (DKA), including rapid or unexplained weight loss, excessive thirst and urination, vomiting, abdominal pain, drowsiness, deep or rapid breathing, or a fruity smell on the breath. Type 1 diabetes can present at any age and requires prompt assessment — HbA1c alone is not used to diagnose it.

Consider speaking to a GP or specialist if:

• You are interested in a more detailed metabolic assessment, including a fasting lipid profile, liver function tests, fasting plasma glucose, or — where clinically indicated — an OGTT. Note that fasting insulin and HOMA-IR are not routinely recommended by NICE in primary care and are not available as standard NHS tests; if you wish to explore these, a private metabolic clinic may be appropriate

• You are considering significant dietary changes (such as a very low-calorie or ketogenic diet) and have existing health conditions or are taking glucose-lowering medications

• You are using a CGM and have concerns about glucose variability or frequent high readings

If you are pursuing a longevity-focused approach to HbA1c optimisation inspired by clinicians such as Peter Attia, it is advisable to do so in partnership with a healthcare professional who can contextualise your results within your full clinical picture. Private GP services and specialist metabolic clinics are available in the UK for those seeking more detailed preventive health assessments.

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