Fasting Glucose and HbA1c: Reading Your Metabolic Health

Fasting glucose is a snapshot: your blood sugar after not eating overnight. HbA1c (glycated haemoglobin) is different and complementary — it reflects your average blood sugar over roughly the previous two to three months, because glucose sticks to haemoglobin in proportion to how much is around. Together they show both the current level and the recent trend.

Standard thresholds mark a continuum: a fasting glucose of 100–125 mg/dL (5.6–6.9 mmol/L) or an HbA1c of 5.7–6.4% is 'prediabetes'; higher is diabetes (American Diabetes Association, 2024). But risk does not switch on at a line — it rises across the range, which is why the numbers matter even when they are 'not quite' abnormal.

When blood sugar runs high, glucose reacts with proteins throughout the body — a process called glycation that forms 'advanced glycation end-products.' Over time this stiffens and damages tissues, especially the delicate lining of blood vessels, the kidneys, nerves and the retina. HbA1c itself is a glycation product, which is why it doubles as both a marker and a small window onto that damage.

The consequences reach far beyond a diabetes label: elevated glucose drives cardiovascular disease, kidney and nerve damage, and is linked to cognitive decline — much of it accumulating quietly during the years of 'just slightly high' readings.

Large pooled studies show the risk climbs continuously. Across 102 prospective studies, higher fasting glucose was associated with greater risk of cardiovascular disease, with risk rising even within the pre-diabetic range (Emerging Risk Factors Collaboration, 2010). In adults without diagnosed diabetes, HbA1c predicted future heart disease and death, adding information beyond fasting glucose alone (Selvin et al., 2010).

So these are not just diabetes tests — they are graded markers of how well your metabolism is protecting your vessels and organs over time.

The good news is that metabolic drift is highly modifiable. In two landmark randomised trials, structured lifestyle change — modest weight loss, more physical activity and a better diet — cut the progression from prediabetes to type 2 diabetes by roughly half or more (Tuomilehto et al., 2001; Diabetes Prevention Program Research Group, 2002), outperforming medication in those studies.

Practically: losing excess weight (especially around the waist), moving regularly, building muscle, and reducing refined carbohydrates and sugary drinks all lower glucose and HbA1c. Get both numbers tested periodically and, if they are creeping up, act early and discuss them with a qualified professional — the earlier the intervention, the more of the trajectory you can bend.