Lack of Sleep Affects the Severity of Type 2 Diabetes

Summarized by Robert W. Griffith, MD
November 6, 2006

Summary

Inadequate sleep (too little, or of poor quality) is associated with deterioration in blood glucose control in type 2 diabetics.

Introduction

Evidence already exists that sleep loss increases the risk of occurrence of diabetes (see the first link below). "Sleep loss" may be a shorter duration of sleep, or poor quality sleep. A new study has examined the effects of both these factors on the severity of existing type 2 diabetes in African Americans. It's been published in the Archives of Internal Medicine, and we summarize the main points here.

What was done

The investigators interviewed 298 volunteers with type 2 diabetes at the University of Chicago Hospital. Patients with diabetes diagnosed within the past year, those with incomplete responses or no recent HbA1c level, and those who slept more than 12 hours a night were eliminated from the study. This left 204 participants.

There were 161 African Americans, 38 white, and 5 of other ethnicity in this collective. Because there are well-known ethnic differences in diabetic risk and sleep patterns, the investigators decided to limit the study to the 161 African Americans, to simplify the interpretation of the findings.

In a 45-minute interview, the patient's diabetes was characterized as being without complications, or having one or more major complications - neuropathy, retinopathy, nephropathy, coronary heart disease, or peripheral vascular disease.

The Pittsburgh Sleep Quality Index (PSQI), which is a 19-item questionnaire, was used to score sleep quality, which ranged from 0 to 21 points. A score greater than 5 indicates poor sleep quality. The actual number of hours of sleep for weeknights and weekends were also recorded. "Sleep debt" was calculated as the difference between actual weekday sleep duration and the preferred sleep duration.

The severity of diabetes was assessed by means of the hemoglobin A1c level, or HbA1c¹. Values were obtained from the medical charts. Risk for a breathing-related sleep disorder (e.g. sleep apnea) was assessed, along with a simple test for depression.

What was found

There were 42 men and 119 women in the collective; their average age was 57, their average body mass index (BMI) was 35.8 (i.e. in the severely obese range), and the average duration of their diabetes was 11 years.

The average HbA1c level was 8.3%; one in four had a level below 7%, the recommended upper level, indicating that their diabetes was controlled.

Of the 161 participants, 71% experienced poor sleep (a PSQI score above 5). Average sleep duration was 6 hours; 22% of the patients got at least 7 hours, and 6% got 8 hours on weeknights.

Thirty-nine patients said their sleep was frequently interrupted by pain; they were excluded from the rest of the analyses. After they were omitted, there were still 67% in the remainder who had poor sleep quality.

Higher HbA1c levels were associated with higher PSQI scores (i.e. lower sleep quality), and more complaints of shortage of sleep. In those patients without diabetic complications, perceived sleep debt was linked with higher HbA1c levels. If the debt reached 3 hours a night, the HbA1c was likely to be raised by 1.1%. In patients with at least one major diabetic complication, sleep quality (PSQI score), but not sleep debt, was associated with increased HbA1c; an increase of 5 points on the PSQI was associated with an increase in HbA1c level of 1.9% (going from an average of 8.7% for these patients to 10.6%).

The depression test scores showed that symptoms of depression accompanied poor sleep quality at an equal rate. BMI values, on the other hand, were unrelated to sleep quality or duration.

What these results mean

The results show that inadequate sleep (not enough, or poor quality sleep) is associated with a deterioration of blood glucose control, as expressed by an increased HbA1c.

One should remember that this is an "association" - the results themselves don't indicate which direction the cause and effect actually take. For instance, excessive urination at night, as is common in diabetics, could interrupt sleep and result in poor quality or even shortening of sleep.

As we pointed out earlier, numerous studies have shown that sleep deprivation increases the likelihood of developing diabetes. So it seems highly likely that poor sleep is responsible for the worsening of diabetic control in this study. However, the findings beg the obvious question: would optimizing sleep duration and quality in diabetics improve their glucose control?

Until the necessary studies are completed to test this point, it would be prudent for diabetics to try to ensure that they get adequate, good quality sleep. There are plenty of sources for advice on this - see the related links below.

Source

• Role of sleep duration and quality in the risk and severity of type 2 diabetes mellitus. KL. Knutson, AM. Ryden, BA. Mander, E. Van Cauter , Arch Intern Med, 2006, vol. 166, pp. 1768--1774

Footnotes
1. HbA1c is shorthand for a type of hemoglobin, the oxygen-carrying element in red blood cells. (Hb stands for hemoglobin, and A1c is the designation of the subtype.) It's important because glucose binds to HbA1c and is only released very slowly, so that the HbA1c represents the average blood glucose level over the previous 4 weeks. This makes its measurement far more valuable than just a single blood sugar measurement, which can vary a lot depending on when your last meal was and what it contained.

Related Links
Sleep Duration as a Risk Factor...
How to Get a Good Night's Sleep
Insomnia: 41 Simple Tips

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