A new study may help explain why being “apple-shaped”, that is carrying excess weight around the middle, is more closely linked with kidney disease than being pear-shaped, regardless of BMI. Researchers in the The Netherlands found that people with apple-shaped bodies are more likely to have poorer kidney function, plus lower blood flow and higher blood pressure in the kidneys.
Arjan Kwakernaak and colleagues, of the University Medical Center Groningen, report their findings in the 11 April online before print issue of the Journal of the American Society of Nephrology (JASN).
Scientists already know that carrying excess fat around the middle is more closely linked to kidney disease than carrying it around the hips, but the underlying mechanisms are not well understood.
Kwakernaak and colleagues set out to examine what these mechanisms might be by looking at waist-to-hip ratios (WHRs) and measures of kidney health (“renal hemodynamics”) in 315 healthy people with an average body mass index (BMI) of 24.9 kg/m2.
A BMI between 18.5 and 24.9 kg/m2 is considered normal weight, and WHR is a measure of how much body fat is carried around the middle (central adiposity).
The researchers found that the more apple-shaped a person was (higher WHR), the lower their kidney function (as measured by GFR), plus the lower their kidney blood flow and the higher their kidney blood pressure, even after taking into account possible influencing factors.
“WHR was associated with lower GFR, lower effective renal plasma flow, and higher filtration fraction, even after adjustment for sex, age, mean arterial pressure, and BMI,” write the authors.
Glomerular filtration rate (GFR) is the volume of fluid the kidneys can filter in a given amount of time. It is used to assess the excretory function of the kidneys.
Kwakernaak says in a press statement:
“We found that apple-shaped persons — even if totally healthy and with a normal blood pressure — have an elevated blood pressure in their kidneys. When they are also overweight or obese, this is even worse.”
He and his colleagues suggest it is the elevated blood pressure in the kidneys that may explain why apple-shaped people have a higher risk for kidney disease later in life.
They propose such individuals may benefit from treatments that reduce blood pressure in the kidneys.
Previous studies have suggested restricting salt intake can reduce kidney blood pressure, as can drugs that help regulate the “renin-angiotensin-aldosterone system”.
“Our current data suggest that such interventions could be particularly useful in subjects with a central body fat distribution,” says Kwakernaak.
Meanwhile, a UK study published online a week earlier in JASN, found that being overweight starting in young adulthood may significantly increase individuals’ risks of developing kidney disease by the time they become seniors.
Written by Catharine Paddock PhD