Dear Dietitian

Why are my blood glucose readings higher in the mornings?

Please help me to understand why my blood glucose readings are higher in the mornings than they were the previous night. Last night my reading at 10.30 pm was 5.6 and this morning it was 7.6. I was told it was residual sugar in my body. But surely if it was residual sugar it would be less than the original reading?

An interesting question with a complex answer.

It is important to realise that food is just one factor that affects blood glucose levels. There is a relationship between food eaten and the resulting rise (while absorption of food is dominant) and then fall (while the rate of removal of glucose into cells as fuel or storage is dominant) of blood glucose levels. But once the blood glucose level falls to a normal level it does not keep on falling unless it is driven by an excessive amount of insulin.

The liver has the role of maintaining the blood glucose level sufficiently high so that cells, like those in the brain that are dependent on glucose as fuel, can keep working properly. The liver can keep the blood glucose level from falling in the short term (a few hours) by releasing stored glucose (involving break-down of glycogen).

For a longer term need (such as overnight) the liver works by making new glucose from aminoacids in the blood. The aminoacids used up are replaced by breakdown of muscle proteins.

To understand more, we need to consider the actions of insulin. Everyone seems to know that insulin is required to get glucose to enter cells for fuel or storage and so the link with food intake is easy to understand.

But much less widely understood is the fact that insulin also controls the action of the liver in releasing stored glucose or making new glucose. Insulin is very important here.

If there is insufficient insulin, the liver will make an excess of glucose and this will, for example, lead to an abnormally high blood glucose level in the early morning.

Whether it is just a little bit too high as in your reading, 7.6, or very high like 15, depends on how much reduced the action of insulin is.