People with ‘healthy’ obesity have a 66% increased risk of chronic kidney disease compared to metabolically healthy individuals with normal weight, finds a new study led by the University of Birmingham.

Those that are metabolically healthy (do not suffer with metabolic conditions such as hypertension, diabetes, high cholesterol or cardiovascular disease) and are overweight but do not have obesity are at a 30% risk of chronic kidney disease compared to healthy people with normal weight, the study found.

The research also found that the increased risk was greater in those aged under 65, while also the more the number of the metabolic complications a person has the higher risk of chronic kidney disease even in the normal weight range.

The research, published in the American Journal of Kidney Disease, was carried out in collaboration with University Hospitals Birmingham NHS Foundation Trust and the University of Warwick.

The retrospective population-based cohort study examined the GP records of around 4.5 million individuals from the UK and tracked their health over an average of almost five-and-a-half-years. Of the 4.5 million individuals, 1,040,921 (23.4%) and 588,909 (13.2%) were metabolically healthy overweight and metabolically healthy obese, respectively.

Chronic kidney disease has a major impact on global health and cost the UK National Health Service £1.45 billion in 2009-2010. In 2017, 697.5 million people in the world had the disease, and it accounted for 1.2 million deaths. The prevalence of chronic kidney disease increased by almost 30% between 1990 and 2017, while the number of deaths caused by the condition rose by 41.5% in the same period. Similarly, the prevalence of obesity is also on the rise, tripling between 1975 and 2016.

First author Dr. Jingya Wang, Research Fellow at the University of Birmingham, said: “Our results demonstrate that individuals with metabolically healthy obesity might have a higher risk of developing chronic kidney disease compared with normal weight individuals, especially those younger than 65 years.

“Looking to the future, a clinical trial of a weight loss intervention could be considered in these individuals to help us establish whether this can reduce their high risk of chronic kidney disease.”

Dr. Abd Tahrani, Senior Lecturer in Metabolic Endocrinology and Obesity Medicine at the University of Birmingham, says: “It is likely that weight loss in people with metabolically healthy obesity is likely to reduce their risk of chronic kidney disease as it will also reduce their risk of future type 2 diabetes, and hypertension, both of which can worsen kidney function and result in chronic kidney disease, however this needs to be examined in future trials.

“In addition, we know from previous trials that weight loss in individuals with normal weight can reverse non-alcoholic fatty liver disease for example, hence weight loss could offer an important strategy to prevent obesity complications in this population.”

Dr. Krish Nirantharakumar, also of the University of Birmingham, said: “Furthermore, our results suggest that individuals with normal weight who have metabolic abnormalities are also at a higher risk of chronic kidney disease and as such might benefit from meticulous metabolic control to reduce the risk of developing the condition.

“Ultimately, chronic kidney disease is largely preventable, and therefore, it is important to identify and treat the underlying modifiable causes and risk factors.”

This new study follows previous research led by the University of Birmingham and published in 2017 in the Journal of the American College of Cardiology which showed that individuals living with obesity who are metabolically healthy have an increased risk of cardiovascular disease events compared to those who are normal weight without metabolic abnormalities.

Neil Thomas, Professor in Epidemiology and Research Methods at the University of Birmingham, adds: “This new study and our previously published study together demonstrate that individuals who are metabolically healthy can develop organ damage over time.

“Therefore, metabolically healthy obesity should not be considered ‘benign’ or harmless and addressing obesity in metabolically health people might reduce organ damage including chronic kidney disease.”