Now, new research at the University of Michigan Health System and the Veterans Affairs Ann Arbor Healthcare System indicates that they also tend to have higher levels of glucose (blood sugar).
That could put these so-called "non-dippers" at greater risk for developing diabetes and other diseases, which in turn raises the risk of cardiovascular problems, researchers say.
"We found that non-dippers experienced a higher likelihood having increased fasting glucose than people whose blood pressure dips by more than 10 percent overnight," says Meredith Montero, a third-year medical student at the University of Michigan Medical School, who is presenting the research May 13 at the annual meeting of the American Geriatrics Society in Orlando.
"This means that health care providers may want to monitor these patients' glucose more closely and emphasize to them the importance of monitoring their blood pressure," Montero says.
Researchers studied 51 patients ages 60 to 80 who have high blood pressure, or hypertension. Of those, 20 were non-dippers, whose blood pressure does not drop by 10 percent at night. Most people in the general population are "dippers," but it is common for people with hypertension to be non-dippers.
Both groups had nearly identical average blood pressure levels over the 24-hour period they were studied, but the non-dippers did not have the overnight reduction in their blood pressure experienced by the other 31 subjects.
Two blood sugar measures – fasting glucose and two-hour oral glucose tolerance tests – differed for the two groups, the study found. The fasting glucose level for the dippers was 95 mg/dl on average; their two-hour oral glucose tolerance level was 133 mg/dl. Those numbers were 102 and 144 for non-dippers, respectively.
A fasting glucose level higher than 125 is indicative of diabetes. Levels of 110-125 may indicate pre-diabetes, a condition in which blood glucose levels are higher than usual but are not at the level of diabetes. People with pre-diabetes can prevent the onset of diabetes with the help of exercise, weight loss and diet changes.
In addition to the potential for developing diabetes, the higher glucose and insulin rates could contribute to the increased rate of cardiovascular problems among non-dippers, says Mark Supiano, M.D., professor of geriatric medicine in the U-M Medical School's Department of Internal Medicine, director of the Geriatric Research, Education and Clinical Center (GRECC) at the Veterans Affairs Ann Arbor Healthcare System, and Montero's faculty mentor on this study.
"Since higher glucose levels are tied to such serious health conditions, it is important that we monitor these levels in people who appear to be at higher risk, such as people whose blood pressure does not drop significantly overnight," Supiano says.
The research was supported by the Hartford Foundation/American Federation for Aging Research, and by GRECC at the VA Ann Arbor Healthcare System. Montero's summer research program was supported by the American Federation for Aging Research Medical Student Geriatric Scholars program.
Reference: American Geriatrics Society annual meeting, paper abstract P20.