Normal blood sugar levels chart by age
The following table shows normal blood glucose levels by age group, aligned with NHS and WHO diagnostic criteria. Blood glucose in the UK is measured in millimoles per litre (mmol/L). Note that while age affects average blood sugar readings, the diagnostic thresholds for prediabetes and diabetes do not change with age — the same clinical cut-offs apply regardless of whether you are 30 or 70.
| Age group | Normal fasting glucose | Normal 2hr post-meal | Typical HbA1c |
|---|---|---|---|
| 18–29 | 3.9–5.4 mmol/L | Below 7.8 mmol/L | 27–38 mmol/mol |
| 30–39 | 3.9–5.5 mmol/L | Below 7.8 mmol/L | 28–40 mmol/mol |
| 40–49 | 3.9–5.6 mmol/L | Below 7.8 mmol/L | 29–41 mmol/mol |
| 50–59 | 3.9–5.7 mmol/L | Below 7.8 mmol/L | 30–42 mmol/mol |
| 60–69 | 3.9–5.8 mmol/L | Below 7.8 mmol/L | 31–43 mmol/mol |
| 70+ | 4.0–6.0 mmol/L | Below 7.8 mmol/L | 32–44 mmol/mol |
Fasting blood glucose 5.5–6.9 mmol/L = prediabetes (impaired fasting glucose). Fasting glucose 7.0 mmol/L or above on two separate occasions = type 2 diabetes. HbA1c 42–47 mmol/mol = prediabetes. HbA1c 48 mmol/mol or above = diabetes. These thresholds apply to all adults regardless of age.
Understanding your blood sugar reading
Blood glucose can be measured in several ways, each giving different information:
| Test type | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting glucose (8+ hours) | Below 5.5 | 5.5–6.9 mmol/L | 7.0+ mmol/L |
| 2-hour post-meal | Below 7.8 | 7.8–11.0 mmol/L | 11.1+ mmol/L |
| Random glucose | Below 7.8 | 7.8–11.0 mmol/L | 11.1+ mmol/L |
| HbA1c | Below 42 mmol/mol | 42–47 mmol/mol | 48+ mmol/mol |
Does blood sugar increase with age?
Yes — and this is one of the most important but least-discussed aspects of metabolic ageing. Average fasting blood glucose levels rise gradually across the lifespan for several interconnected reasons:
Declining insulin sensitivity. Cells become progressively less responsive to insulin with age — a condition called insulin resistance. The pancreas compensates by producing more insulin, but over time this capacity is strained. This is the central mechanism behind age-related increases in blood sugar and the rising prevalence of type 2 diabetes with age.
Reduced lean muscle mass. Skeletal muscle is the primary site of glucose disposal — it absorbs a large proportion of blood glucose after eating. As muscle mass declines with age (sarcopenia), this disposal capacity shrinks, causing blood glucose to remain elevated longer after meals. This is why resistance training has a directly beneficial effect on blood sugar regulation.
Changes in pancreatic function. The insulin-producing beta cells of the pancreas gradually decline in both number and function with age, reducing the peak insulin response to meals.
Increased visceral fat. Age-associated fat redistribution toward the abdomen — particularly visceral fat around the organs — is strongly associated with insulin resistance and elevated blood sugar.
Prediabetes — blood glucose in the range between normal and diabetes — is reversible in most cases. The NHS Diabetes Prevention Programme (DPP) has shown that intensive lifestyle intervention (diet, weight loss, exercise) can prevent or significantly delay progression to type 2 diabetes. If your fasting glucose is 5.5–6.9 mmol/L or HbA1c 42–47 mmol/mol, action now is meaningful.
What is a normal fasting blood sugar for a non-diabetic?
A normal fasting blood sugar level for a non-diabetic adult is below 5.5 mmol/L, with optimal being in the range of 4.0–5.2 mmol/L. A fasting glucose consistently in the 5.5–6.9 mmol/L range, while not diabetic, indicates impaired fasting glucose (prediabetes) and warrants dietary and lifestyle intervention.
It is worth noting that some entirely healthy adults — particularly those who are lean, physically active and eat a low-carbohydrate diet — may have fasting glucose readings as low as 3.5–4.5 mmol/L. This is not a cause for concern provided there are no symptoms of hypoglycaemia.
Blood sugar levels after eating: what is normal?
After eating, blood glucose rises in response to carbohydrate absorption. In a healthy individual, this post-meal (postprandial) glucose spike is rapidly controlled by insulin. What is considered normal blood sugar 1 hour after eating is typically below 8–9 mmol/L; at 2 hours, below 7.8 mmol/L; at 3–4 hours, returning to baseline fasting levels (below 5.5 mmol/L).
Post-meal blood sugar spikes that consistently exceed 10 mmol/L at 1 hour, or remain above 7.8 mmol/L at 2 hours, are a sign of impaired glucose tolerance even if fasting glucose is normal. Wearing a continuous glucose monitor (CGM) is increasingly accessible and can reveal post-meal patterns that standard HbA1c testing misses.
HbA1c: the long-term blood sugar marker
HbA1c (glycated haemoglobin) measures the average blood glucose over the preceding 2–3 months, reflecting how much glucose has become attached to red blood cells. It is the most reliable long-term indicator of blood sugar control and cardiovascular risk from hyperglycaemia.
A normal HbA1c for a non-diabetic adult is below 42 mmol/mol (below 6.0% in the old DCCT percentage scale). An HbA1c of 42–47 mmol/mol (6.0–6.4%) indicates prediabetes. An HbA1c of 48 mmol/mol (6.5%) or above on two separate tests is diagnostic of type 2 diabetes.
For context, average HbA1c in the UK population rises by approximately 1–2 mmol/mol per decade of age, reflecting the gradual age-related decline in insulin sensitivity described above.
How to lower blood sugar naturally
Resistance training is the most underrated tool for blood sugar management. Each bout of resistance exercise depletes muscle glycogen, opening up glucose storage capacity and increasing insulin sensitivity for 24–48 hours. For people with prediabetes, 2–3 sessions of resistance training per week can produce meaningful HbA1c reductions.
Post-meal walking — even 10–15 minutes of light walking after eating — dramatically blunts post-meal glucose spikes by activating muscle glucose uptake through a non-insulin-mediated pathway. This is one of the most accessible and evidence-based interventions available.
Dietary fibre — particularly soluble fibre from oats, legumes and vegetables — slows glucose absorption, reducing post-meal spikes. The Mediterranean diet and low-glycaemic-index diets both improve fasting glucose and HbA1c in people with prediabetes.
Weight loss — for overweight or obese individuals, 5–10% body weight loss is associated with significant improvements in insulin sensitivity and HbA1c. The NHS DiRECT trial demonstrated that intensive dietary weight loss can put type 2 diabetes into remission in some individuals.
Intermittent fasting has emerging evidence for improving insulin sensitivity and lowering fasting glucose, independent of calorie restriction. Time-restricted eating (eating within an 8–10 hour window) has been shown to reduce HbA1c in adults with prediabetes.
How is your metabolism ageing?
Take our full body age test to explore how your blood sugar regulation, gut health, hormones, heart and more compare to your chronological age.
▶ Get My Personalised Body Age Report