People with prehypertension are not at increased risk of kidney disease if their body mass index (BMI) is under 30.0 kg/m2, a first-ever examination of the combined effect of blood pressure and body weight on the risk of kidney disease shows.

The study, by a team of medical researchers at the Norwegian University of Science and Technology (NTNU) is available as a pre-publication article online from the American Journal of Kidney Diseases.

Prehypertension is a relatively new medical classification introduced in 2003 in the Seventh Report of the Joint National Committee on High Blood Pressure (JNC-7), and is defined as systolic blood pressure of 120 to 139 mm Hg or diastolic BP of 80 to 89 mm Hg. Studies from the United States and Asia have shown that prehypertension can increase the risk of serious kidney disease, but because more than 30 percent of the US and European populations can be classified as prehypertensive, treating everyone with this condition would be an enormous undertaking, the researchers observed.

At the same time, obesity is also known to lead to end-stage renal disease (ESRD) and death from chronic kidney disease (CKD) as a result of diabetes and hypertension. These increased risks have led medical researchers to consider whether people with prehypertension should be considered for treatment if they have other cardiovascular risks, such as obesity.

Using data from nearly 75,000 participants in the HUNT 1 study, the first Health Study in Nord-Trøndelag, a team of NTNU researchers led by Dr. John Munkhaugen were able to further clarify the risks of ESRD in overweight individuals.

"We found a strong, independent and continuous association with both BP and body weight" on the risk of treated ESRD or chronic kidney disease related deaths, the researchers wrote. However, "prehypertensive participants increased their risk of treated ESRD or CKD-related death only if BMI was greater than 30.0 kg/m2."

The strength of the NTNU study is its ability to use data from the two-decade old HUNT 1 study, which provides researchers the ability to follow up on measurements made 20 years ago. The HUNT 1 study involved 88.2 percent of all inhabitants 20 years or older in Nord-Trøndelag county, in mid-Norway. The data were linked to the Norwegian Renal Registry and to the Cause of Death Registry in Norway.

Source: NTNU