Sleep Factors and Diabetes Severity

CHICAGO, Sept. 18 -- African Americans with type 2 diabetes who are chronically sleep deprived may pay the price in the form of impaired glucose control and more serious complications of type 2 diabetes, researchers here found.

Among African Americans with type 2 diabetes, poor sleep quality and sleep debt were associated with significantly higher glucose levels, as measured by glycosylated hemoglobin (HbA1c), reported Eve Van Cauter, Ph.D., and colleagues of the University of Chicago and Northwestern University.

Patients who reported having higher sleep debts or lower sleep quality than others had generally poorer glucose control, after data were controlled for age, gender, body mass index, insulin use, and presence of major complications.

"Sleep curtailment has become increasingly prevalent in modern society, and it cannot be excluded that this behavior has contributed to the current epidemic of type 2 diabetes," the investigators wrote in a special issue of the Archives of Internal Medicine devoted to sleep and its health consequences.

In an accompanying editorial, Phyllis C. Zee, M.D., Ph.D., and Fred W. Turek, Ph.D., wrote that "these are notable findings for health care professionals and patients because they indicate not only that voluntary chronic partial sleep deprivation may increase the risk for diabetes mellitus, but also that continuing this pattern renders it more difficult to treat the condition."

The editorialists, who were not involved in the study, are both sleep researchers at Northwestern Feinberg School of Medicine.

Dr. Van Cauter and colleagues performed a cross-sectional study of the effects of sleep debt and poor-quality sleep in 161 African American adults.

"There are well-documented ethnic differences in both diabetes risk and sleep," the authors noted. Their original cohort included members of other racial and ethnic groups, but only African Americans were represented in numbers large enough for a meaningful analysis, they said.

The investigators interviewed the volunteers, reviewed their medical charts for HbA1c levels, and used the patient-rated Pittsburgh Sleep Quality Index to assess their sleep levels.

The authors also calculated "perceived sleep debt," which they defined as the difference between each patient's preferred and actual weekday sleep duration.

Excluding participants who reported sleep disruption from pain, they found that patients slept an average of 6.0 + 1.6 hours per weeknight, and that 71% of the participants had poor-quality sleep, as indicated by a Pittsburgh Sleep Quality Index score above 5.

In participants who did not have diabetic complications such as retinopathy, neuropathy, nephropathy, coronary artery disease, or peripheral vascular disease, glycemic control was associated with perceived sleep debt, but not with Pittsburgh Sleep Quality Index score.

For patients with a perceived sleep debt of three hours per night (for example, someone who reported needing eight hours but getting only five), the predicted increase in HbA1c level was 1.1% above the median.

In patients who had one or more diabetic complications, HbA1c levels were associated with Pittsburgh Sleep Quality Index score, but not with perceived sleep debt. In this group, the predicted increase in HbA1c level for a 5-point increase in the sleep index score was 1.9% above the median.

"In our sample, sleep duration and quality were significant predictors of HbA1c, a key marker of glycemic control," the investigators wrote. "Combined with existing evidence linking sleep loss to increased diabetes risk, these data suggest that optimizing sleep duration and quality should be tested as an intervention to improve glucose control in patients with type 2 diabetes."

The authors noted that 17% of men in the sample and 27% of women were at high risk for a sleep-related breathing disorder such as sleep apnea, and that the prevalence of this disorder in their sample may have been underestimated. They noted, however, that when the controlled for sleep-related breathing disorders, the association between HbA1c levels and other sleep variables held up, suggesting that apnea or related conditions were not the chief mediators in the relationship between glucose control and sleep.