Q Regular blood tests show that I have a very low white blood cell count, around 0.6 per litre (usual count 3-6). I know white blood cells are linked to immunity but, despite running long distances, I never become ill. Is this low white cell count a result of my running? Does it put me at risk in any way?
A Studies comparing endurance athletes with non-athletes show that their immune function is more similar than you might imagine. However, resting circulating numbers of white blood cells – which are important in your defence against foreign invaders such as bacteria and viruses – are generally lower “within the normal clinical range” in endurance athletes.
Scientists are not sure why this is, but it could be due to haemodilution. When blood plasma volume expands – as a result of training – the concentration of white blood cells may drop. Immune cell death (apoptosis) may also increase with heavy training.
Studies have revealed that white blood cell counts are lowered in military personnel during periods of heavy training but these usually return to normal levels after only a couple of days’ rest. You should have your white blood cell count checked after a similar period of rest.
You mention that your white blood cell count is 0.6/litre. This is well below the normal clinical range. In endurance athletes a white blood cell count of this level often indicates overtraining or postviral fatigue; athletes with this blood count also report frequent respiratory tract infections.
Given that you don’t mention typical symptoms of overtraining – such as underperforming and prolonged fatigue – and you “never become ill”, it is unlikely that overtraining accounts for your low white blood cell count so you should discuss other possible causes and treatment with your GP.
It does not necessarily follow that you will become ill if your white blood cell count is below the normal clinical range – you must be exposed to a virus first. That you never become ill, despite having a low white blood cell count, only goes to demonstrate this fact.
— Dr Neil Walsh, Senior Lecturer, School of Sport, Health & Exercise, University of Wales, Bangor