Obesity surgery might help get high blood pressure under control.

The finding comes from John Fernstrom, PhD, and colleagues of the University of Pittsburgh's medical school.

They report that among very obese people, blood pressure often dipped after weight loss surgery, especially for people with previously untreated high blood pressure.

The results could help show which patients "are likely to experience substantial improvements in blood pressure" after gastric bypass surgery and possibly no longer need medicine to control blood pressure, Fernstrom says in a news release.

Fernstrom's study appears in the Archives of Surgery. It comes on the heels of a report by other researchers showing that weight loss surgery may help avoid heart disease and stroke.

Before and After Surgery

Fernstrom's team checked the medical records of 347 people who got weight loss surgery.

The patients were "very obese" before surgery, with an average BMI (body mass index) of 50-55, the researchers write. A BMI of 30 or more is considered obese. Being overweight or obese can boost blood pressure, the researchers write.

Before gastric bypass surgery, 192 patients had high blood pressure. Of those patients, 103 were taking prescription drugs to control their blood pressure. High blood pressure was defined as a reading of 140 or higher for systolic pressure (top number), 90 or higher of diastolic pressure (bottom number), or both.

Average BMI fell to 35 during the first 12-18 months after surgery. That's a big drop, but a BMI of 35 is still obese, Fernstrom and colleagues note.

After surgery, 92 patients still had high blood pressure, with 68 taking blood pressure medicines. Of the 103 patients taking blood pressure drugs before surgery, 35 stopped taking those drugs in the months after surgery, the study shows.

Biggest Improvements

The biggest blood pressure improvements were seen in patients who had had untreated high blood pressure before surgery, write Fernstrom and colleagues.

Patients with normal blood pressure and those already being treated for high blood pressure had less room for improvement. Diastolic blood pressure improved more than systolic blood pressure.

The researchers checked the patients' medical charts for nearly two years after surgery. It's not yet clear if the patients' BMI and blood pressure improvements lasted longer than that, the researchers note.

The patients' medical charts don't track changes in the patients' eating habits or physical activity, which may also affect blood pressure.