Why is my morning bg high? What are dawn phenomenon, rebound, and Somogyi effect?

This section is written by Charles Coughran <ccoughran(AT)ucsd.edu>.

There are three main causes of high morning fasting bg. In decreasing order of
probability they are insufficient insulin, dawn phenomenon, and Somogyi
effect (aka rebound). Insufficient or waning insulin is simple. If the
effective duration of intermediate or long acting insulin ends sometime
during the night, the relative level of circulating insulin will be too low,
and your blood sugars will rise.

Dawn phenomenon refers to increased glucose production and insulin resistance
brought on by the release of counterregulatory hormones in the early morning
hours near waking. It happens in normal people as well as in diabetics; in
nondiabetics it shows up as measurably increased insulin secretion around
dawn. Dawn phenomenon is variable in strength both within the population and
over time in individuals. It can show up as either high fasting glucose
levels or an increased insulin requirement to cover breakfast compared to
equivalent meals at other times of day.

Somogyi effect refers to a rebound in bg after nocturnal hypoglycemia which
occurs during sleep with the patient not experiencing any symptoms. The
hypoglycemia triggers the release of counterregulatory hormones. Somgoyi
effect appears to be less prevalent than previously thought. While it does
occur, some episodes of hyperglycemia following hypoglycemia are actually
waning insulin levels following an insulin peak with medium acting insulin.
This can be difficult to sort out.

The best way to sort it out is to test every couple of hours from bedtime to
morning.

    If your bg rises all, or much of the night, it is a lack of circulating
    insulin.

    If it is stable all night, but rises sharply sometime before you wake in
    the morning, it is dawn phenomenon.

    If your bg declines to the point of a hypoglycemic reaction, it is
    *possibly* Somogyi effect.

You may have to test on several nights to nail the problem. Once you have
figured out the problem you and your doctor can discuss changes in your
insulin regimen to correct it. The answer depends critically on your
particular circumstances.

Mayer Davidson, in _Diabetes Mellitus: Diagnosis and Treatment_ (p 252 in the
3rd edition) says that Somogyi effect rarely causes fasting hyperglycemia,
and cites studies.