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University of Iowa News Release


Nov. 29, 2006

UI Research Links Less Sleep With Higher Body Mass Index

University of Iowa researchers conducting a long-term health study in one rural Iowa county report an association between short sleep duration and higher body mass index.

The study results are based on data collected from 1999-2004 as part of the UI-led Keokuk County Rural Health Study, an ongoing, population-based study of health status and environmental and occupational exposures of residents in Keokuk County in southeast Iowa. The results were published in the September issue of the journal Archives of Internal Medicine. 

Body mass index (BMI) is a measurement of body fat often used to determine obesity. It is calculated by dividing weight in kilograms by height in meters squared. A normal-weight BMI ranges between 18.5 and 24.9; a person whose BMI is 25 to 29.9 is considered overweight; and obese individuals are those whose BMI is 30 or higher.

The UI study data were collected from in-person interviews given to 990 adults living in Keokuk County. Participants were asked about their sleep duration in a typical workday; other questions focused on participants' physical activity, depressive symptoms, alcohol consumption and snoring. Height and weight measurements also were taken and BMI levels were calculated; the mean (average) BMI for the study group was 29.5.

In terms of sleep duration, the largest percentage of participants (34.6 percent) reported getting between seven and 7.9 hours of sleep each night. BMI was highest for participants who reported the shortest sleep duration (less than six hours). BMI among the participants decreased as sleep duration increased.

"On average, for each hour of sleep decrease there was an association of a three-pound increase in weight," said Neal Kohatsu, M.D., (left) a former faculty member in the UI College of Public Health and a principal investigator for the study. Kohatsu is currently chief of the Cancer Control Branch in the California Department of Health Services.

"Are the increases in BMI and people sleeping less directly related? Probably not," said Jim Merchant, M.D., Dr.P.H., (right) Dean of the UI College of Public Health, and one of the study investigators. "But our findings are provocative. They stimulate additional research and raise concern that this is a problem in rural America where obesity rates are higher."

The reasons for the rise of obesity rates in the United States over the past 15 years involve an interaction of genetic, environmental and lifestyle factors, the study authors noted. The researchers' finding that short sleep duration was associated with increased BMI is consistent with previous research, but the UI study may be the first to examine short sleep duration and obesity in a rural population, according to the authors.

"Many national studies say rural populations have a higher BMI rates, and we wanted to explore the associations with sleep habits, as many farmers start before dawn," Kohatsu said.

Obesity is considered a risk factor for high cholesterol, diabetes, hypertension, heart attack, stroke and hardening of the arteries. A higher BMI may also lead to obstructive sleep apnea, said Mark Eric Dyken, M.D., (left) professor of neurology in the UI Roy J. and Lucille A. Carver College of Medicine and director of the Sleep Disorders Center at UI Hospitals and Clinics.

"This study alerts practitioners and patients and justifies that we need to do screenings for sleep apnea in cases of higher BMI," Dyken said. "Having a higher BMI often leads to additional health problems, but if we diagnose and treat people before they start developing these problems, we can push the domino affect the other way."

Keokuk County Rural Health Study researchers will focus their next round of study on nutrition. The will continue to examine sleep and BMI and will track study participants over time to identify particularly vulnerable or high-risk groups, Merchant said.

"We are ready to kick off a new round of study, and we are learning a lot more than we expected with the Keokuk County data," Merchant said. "The data is turning out to be useful in a lot of ways we did not anticipate - the higher BMI/less sleep association is a perfect example."

The Keokuk County Rural Health Study is supported by a grant from the National Institute for Occupational Safety and Health.

STORY SOURCE: University of Iowa Health Science Relations, 5139 Westlawn, Iowa City, Iowa 52242-1178

MEDIA CONTACT: David Pedersen, 319-335-8032, Writer: Krystal Loewe