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New research explains link between body shape and risk of developing kidney stones

30 October 2023

New results from researchers at the University of Oxford published in the Journal of the American Society of Nephrology suggest that carrying excess fat around your middle (often referred to as an ‘apple’ body shape) increases your risk of kidney stones by raising blood calcium levels. 

What is kidney stone disease? 

Kidney stone disease is a common condition affecting around one in ten people whereby hard ‘stones’ made of minerals and salts form in the kidneys. They can often be tiny, but if they get too big or if they move into the tubes connecting the kidney to the bladder, they can cause severe pain and can potentially lead to further complications.  

Although many people will only get one kidney stone in their lifetime, around half of patients who develop a kidney stone will go on to develop more in the future. For some, there is a known genetic cause, but in many cases, we don’t fully understand why kidney stones form, or why they come back. 

Lady with long blond hair wearing a blue top and a blue jacket
Dr Sarah Howles

Leaving no stone unturned to understand causes of kidney stones 

We know from previous studies that people with more body fat are more likely to develop kidney stones but until now it has been unclear why. 

With funding from Kidney Research UK, the National Institute for Health Research and the Wellcome Trust, Dr Sarah Howles and her team used data from the UK Biobank – a collection of health and genetic information from around 500,000 participants – to investigate the link between fat and kidney stone disease. 

The team found that people with a higher body mass index (BMI), and people with a high waist-to-hip ratio (a measure of how much fat tissue is carried around the middle) develop more kidney stones. They then used genetic techniques using data from the UK Biobank and a biobank in Finland called ‘FinnGen’ to show that having a higher BMI or high waist-to-hip ratio directly causes an increased risk of developing kidney stones. 

This new knowledge will help healthcare providers to give better advice to patients as we now know that, even if a patient has a normal BMI, if they are carrying excess fat around their middle, this might increase their risk of developing kidney stones, and they could benefit from lifestyle changes. Our results also suggest that therapies that target fat tissue stores might affect blood calcium levels and prevent patients from developing kidney stones." Dr Sarah Howles

Finding the missing link between fat and kidney stones 

By analysing genetic data, the team found that carrying excess fat tissue around your middle increases the risk of developing kidney stones by raising the levels of calcium in the blood. This in turn can enter the urine and mix with other substances to form solid crystals that can grow into stones. 

What does this mean for the future? 

The team are now working on understanding exactly how body fat can change blood calcium levels as knowledge of these pathways will open the door to developing new treatments to prevent kidney stones from forming. 

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