NEW ORLEANS — Obesity blunts the normal pattern of nocturnal blood pressure dipping, and this might be one mechanism through which obesity contributes to adverse cardiovascular outcomes, findings from a recent study suggest.
Blood pressure normally drops by 10%-20% at night during sleep, compared with blood pressure during waking hours during the day, and studies have shown that nondipping (defined as less than a 10% decrease in blood pressure at night) is associated with increased cardiovascular morbidity and mortality, Dr. Otelio Randall reported in a poster at a meeting sponsored by the International Society on Hypertension in Blacks.
In the study, hourly blood pressure measurements were taken in 200 obese African American patients who were classified into three groups on the basis of their body mass index, in kg/m2: less than 40, 40-49, and at least 50. The average age of the patients was 47 years, and most (83%) were women.
The researchers found that as BMI increased, so did the rates of nocturnal nondipping. The rates of nondipping were 26%, 41%, and 76% for the three BMI categories, respectively. Additionally, 36% of the patients were “reverse dippers,” meaning that their blood pressure actually increased at night, reported Dr. Randall, professor of medicine and cardiology at Howard University, Washington.
The mean percentage of dipping was 8.6% in those with a BMI of less than 40, 8.4% in those with a BMI of 40-49, and 3.9% in those with a BMI of 50 or greater. Those with a BMI of at least 50 had a significantly smaller decrease in nocturnal blood pressure than the other two BMI groups.
Daytime blood pressure for this study was defined as the average of hourly readings between 8 a.m. and 10 p.m., and nighttime blood pressure was defined as the average of hourly readings from 10 p.m. to 6 a.m.
“Nondipping and reverse dipping are known to be associated with the potential risk for target organ damage. The high rates of nondipping and reverse dipping in this obese population reinforces the need to reduce BMI and improve hemodynamic and lipid profiles through lifestyle changes,” Dr. Randall said.