HbA1c in non-diabetics: what a normal value says about your metabolic health

You just got your blood results back. HbA1c: 5.6%. The accompanying note says 'within reference range' and your GP nods approvingly. Still, something nags. Because if you train for a marathon, track your macros to the gram and want to keep your biological age as low as possible, then 'no diabetes' is a very low bar. The question you really want to ask: am I in the optimal zone, or am I slowly sliding off it?

What HbA1c actually measures

HbA1c stands for glycated haemoglobin. Glucose in your blood attaches to the haemoglobin in your red blood cells, and the more glucose floating around on average, the more haemoglobin gets 'sugared'. Because red blood cells live for roughly 8 to 12 weeks, your HbA1c gives an average of your blood sugar over the past 2 to 3 months. A single cheat meal does not skew the value. It is a trend gauge, not a snapshot.

That makes HbA1c powerful for anyone steering their metabolic health by data. The Diabetes Fonds uses it as a core marker to track blood sugar regulation over time, and the WHO applies fixed cut-off values for prediabetes and diabetes. But that is exactly where the catch lies: those cut-offs were designed to detect disease, not to define optimal health.

Normal is not the same as optimal

The Dutch NHG guideline and Thuisarts set the prediabetes threshold at an HbA1c of 5.7% (43 mmol/mol) and diabetes at 6.5% (48 mmol/mol). Everything below that is officially called 'normal'. But normal is a statistical average of a population that is largely insulin resistant, moves too little and eats too much ultra-processed food. Do you want to take that as your benchmark?

My take: for anyone serious about performance and longevity, the real target zone sits clearly below the GP threshold. Research into metabolic health suggests that cardiovascular risk already rises gradually within the 'normal' range, well before you hit the prediabetes line. An HbA1c of 5.6% is no reason to panic, but it is a signal to look more closely.

Interpretation bands for non-diabetics

Use the table below as a guide, not a diagnosis. Always discuss deviating values in consultation with a doctor.

Why your HbA1c sometimes lies

Here is where it gets interesting for athletes, blood donors and biohackers: HbA1c is not a perfect measure. The value depends on how long your red blood cells live, and that is far from equal for everyone.

• Anaemia and iron deficiency: with iron deficiency anaemia, red blood cells live longer and accumulate more glucose. Your HbA1c can then be falsely elevated, while your actual blood sugar is fine.
• Blood donation and haemolysis: if you donate blood regularly or produce red blood cells quickly, your cells are younger on average. That can falsely lower your HbA1c.
• High training load: intensive endurance sport can shorten the lifespan of red blood cells, which can make your HbA1c come out lower than your actual glucose handling justifies.

In other words: a pretty HbA1c can mask a less pretty reality, and vice versa. That is why you never trust a single marker.

Pair it with fasting insulin and glucose

HbA1c tells you the past, but not the whole story. Insulin resistance often develops years before your blood sugar visibly rises: your body simply pumps more and more insulin around to keep your glucose normal. A normal HbA1c with sky-high insulin is a classic blind spot.

That is why you measure your fasting insulin and fasting glucose alongside it. Together you can calculate HOMA-IR, an early indicator of insulin resistance. We go deeper on this in our article on fasting insulin and HOMA-IR. Triglycerides are also a useful addition, because a high triglyceride value often runs alongside insulin resistance.

What you can do about it

Say you sit in the 5.5-5.6% zone. No diagnosis, but an invitation to steer. What works:

• Strength training and post-meal movement: muscles soak up glucose without much insulin. A ten-minute walk after eating does more than you think.
• Carb timing: shift your heavier carbs to moments around your training, when your muscles put them to the best use.
• Sleep and stress: one night of poor sleep measurably worsens your insulin sensitivity the very next day. This is structurally underestimated.
• Measure again: repeat your HbA1c after 3 months, so you capture a full red blood cell cycle and can see the trend.

Want the whole metabolic picture? Then read our pillar on measuring metabolic health, or see how a lipid panel complements your HbA1c reading. Anyone experimenting with nutrition may also find our piece on blood testing before and after the keto diet useful. Your HbA1c is a starting point, not a final verdict; use it to steer with precision.