27/03/2026
Let’s break down the realities of diabetes compromising the immune system and making us at higher risk of infections.
Firstly, the cells most studied with regard to glucose and infection are the neutrophils. As far back as the 1960s it was noted that at a glucose above 9mmol/L caused neutrophils to act a bit drunk and stupid.
Neutrophils at the white blood cells that fight bacterial infections.
So, higher average or actual glucose will absolutely mess with our ability to fight bacterial infections.
Viral illness and diabetes has not been studied in quite the same way, or if it has, I am unable to locate that research. Generally it seems that viral illness is not more frequent in people with elevated glucose (aka diabetes), but it may well be more severe once it is caught. I think the biggest reason for this is because insulin can work like water during an acute viral illness. Mostly because we are dehydrated and our skin circulation shuts down a bit, to shunt blood deeper into our bodies to organs and our brain.
If we manage our glucose tidily and stay on top of hydration during a viral illness, then we should not be any sicker than anyone else.
Now, what does this mean in actual numbers. Well, an average glucose level of 9mmol/L corresponds to an HbA1c of around 7%. So this means that aiming for an HbA1c of 7%, as is the standard in most westernised countries, may not in fact keep us as healthy as possible with regard to bacterial infections.
I am fond of rabbiting on about diabetes not necessarily causing immunocompromise, but given most people in Australia (and the rest of the world) have an HbA1c above 7%, then I am talking rubbish. There is immunocompromise above 9mmol/L, and if it is temporary and not occurring often, then no, I do not think that constitutes immunocompromise.
If we are a bit less intense with our control, then yeah, we may well be more at risk of skin, lung, sinus, throat, bladder and bowel infections.
A good compromise might be aiming for 6.5% if possible, as this lowers the average glucose to around 8mmol/L. Safer for our neutrophils. Seniors, 7% or above is just fine, as hypos pose much more of a risk once one is “mature”.
For T2 folks using meds that do not cause hypos - you can also go hard and aim low (sulfonylureas (gliclazide, glyburide, glimepiride etc) and insulin cause lows, nothing much else does). I encourage my T2 father to aim as close to 6% as possible as his meds do not cause hypos at all. No, I do not treat him, that is naughty, but I encourage use of CGM and not eating trifle for lunch every day.
Personally, because I feel each and every one of my hypos early and can treat early, and am quite insulin sensitive and also exercise a lot, I aim close to 5%, which gives me an average glucose of around 6.3mmol/L. Well below the level at which neutrophils become stupid. No, I am not remotely immunocompromised.
