It is a fact we are all too well aware of. The world, as we know it, continues to grow fat. The popular press has done an excellent job of educating the lay person about the link between obesity and heart disease, high blood pressure, diabetes, etc. However, despite scientific evidence to the contrary, the effect of obesity on the kidneys’ function is less widely known.
Obesity causes a range of dysfunctional effects on the kidney. These effects converge and eventually lead to chronic kidney disease (CKD). In the worst case scenario, affected patients can progress to advanced disease requiring dialysis.
THE ALARMING STATISTICS
The World Health Organization (WHO) considers obesity an international epidemic, stating in 1997 that “obesity’s impact is so diverse and extreme that it should now be regarded as one of the greatest neglected public health problems of our time with an impact on health which may well prove to be as great as that of smoking.”
A quick look at the WHO’s statistics paints a scary picture of what we are up against. It is hard to imagine that in 2008 almost one-quarter of humanity, or 1.5 billion people, were reported to be overweight. Obesity, in combination with diabetes, is the largest epidemic the world has ever faced. It is also the fifth leading cause of deaths worldwide, killing 2.8 million people every year. With this enormous health burden worldwide, the deleterious effects of obesity on kidney function are being increasingly recognized.
Higher body mass index (BMI), a marker of obesity, is an established independent predictor of advanced kidney disease that requires dialysis, even after adjusting for baseline blood pressure and presence of diabetes. In other words, people who are obese are at risk of developing advanced kidney disease because of their obesity alone, and not just because they are more likely to have high blood pressure and diabetes (the two biggest risk factors otherwise for developing kidney disease).
|Obesity causes kidney disease|
Image courtesy of Grant Cochrane/ FreeDigitalPhotos.net
HOW DOES OBESITY CAUSE KIDNEY DISEASE
Obesity is associated with multiple other conditions that are known to compromise kidney function. These conditions are high blood pressure, diabetes, high uric acid levels, high cholesterol levels in the blood, etc. This constellation of findings that often come as a "package deal" with obesity is sometimes also called the metabolic syndrome. Of course, all these conditions, indirectly, will lead to kidney disease.
However, as we can gauge from the evidence quoted in the above section, obesity has been found to cause kidney disease and end stage kidney disease independently of these factors. Hence, the link between obesity and kidney disease is both direct and indirect.
A full explanation of these links risks getting too technical for this blog. Readers who might be interested in the deeper esoteric details are referred to a book chapter I once wrote on this topic. Here is the link for that. For this blog however, I will only briefly mention the direct obesity-related factors that lead to kidney disease.
- Direct effects of obesity on kidney function
Obesity causes changes in the kidneys' blood flow and pressure. These changes begin early in the course of obesity, even before overt effects of obesity on the kidneys are readily apparent. This was shown in a landmark study from a center conducting kidney biopsies on obese patients who presented for weight loss/bariatric surgery in Spain.
One of the keys to unravel obesity’s effect on the kidneys is understanding the concept of body-fat as an independent endocrine organ that produces hormones, rather than simply a passive storage depot for fat. These hormones are broadly referred to as "adipokines", and are the reason for abnormal blood flow/pressure in the kidneys in people with obesity. When these changes persist, they lead to permanent scarring in the kidneys which kick-starts the process of CKD.
There are other ways in which obesity can affect renal function. Obesity and weight gain during adulthood have been known to increase the risk of kidney stones. In women, obesity is an important risk factor for urinary incontinence.
HOW CAN YOU TREAT OBESITY-RELATED KIDNEY DISEASE
One of the hormones (adipokines) that I mentioned above is called, "angiotensinogen". The actions of this hormone can be blocked by a particular class of blood pressure medications called ACE inhibitors. You might be familiar with medications like lisinopril. Well, lisinopril is an ACE inhibitor, and helps in stemming the abnormal blood flow/pressure that is created inside the kidneys due to obesity. Hence, given their possible preventive role, these medications should be proactively considered as first-line agents for treatment of kidney disease and high blood pressure in people with obesity. It goes without saying that weight loss is of utmost importance and can itself cause remission of the disease to a certain extent. However, treatment of associated risk factors like hypertension, diabetes or insulin resistance, sleep apnea, dyslipidemia is also necessary.
Obesity associated kidney disease is a ticking time bomb, and the affected patient stands a huge risk of progression to end stage kidney disease that mandates dialysis, a treatment that is cumbersome and expensive. It is hence imperative that the disease be diagnosed and managed aggressively from the outset.
Veeraish Chauhan, MD, FACP, FASN
Sarasota/ Bradenton, FL