Risks of obesity in children with kidney transplants

Feb 7 2005

Obese children who get kidney transplants tend to be younger, shorter and on dialysis longer than their leaner peers, according to a study in the February issue of the journal Pediatrics.

A review of 6,658 children age 2-17 receiving transplants in the United States, Mexico and Canada between 1987 and 2002 showed that obese children age 6-12 had a five-year mortality rate more than double that of non-obese children the same age: 12.1 percent compared to 5.4 percent respectively.

Across the entire age spectrum studied, obese children who received a transplant were more likely to die of cardiopulmonary disease – the leading cause of death in adult kidney transplant patients – than non-obese children.

"Pediatricians should educate families on the potential risks of excessive weight gain during dialysis and post-kidney transplant," the authors write, noting that obesity is an increasing problem in patients of all ages with end-stage renal disease and one that has received little attention in children.

"These are going to be prematurely old children in a way because they are going to have all these cardiovascular complications and risks at a younger age," says Dr. Coral D. Hanevold, lead author and chief of the Section of (Pediatric) Nephrology at the Medical College of Georgia in Augusta. "These children are more likely to develop hypertension, hyperlipidemia and diabetes at an early age. We are doing transplants so these children can survive, but if they are overweight, that is going to cut into their life expectancy."

She notes that while most children with kidney failure are not overweight, the numbers are increasing: 8 percent of the study children were categorized as obese between 1987-1995 compared with 12.4 percent between 1995-2002.

"Obesity is an increasing problem in children presenting for transplantation and may have an adverse effect on allograft and patient survival," the authors write. Some transplant centers are not performing transplants on extremely obese children because of those concerns. Also, obesity-related kidney disease, which occurs in extremely obese adults, is beginning to be seen in children.

The retrospective study of the North American Pediatric Renal Transplant Cooperative Study was done in conjunction with Dr. Mark M. Mitsnefes, Division of Nephrology and Hypertension, Cincinnati Children's Hospital Medical Center in Ohio and The EMMES Corporation, a Rockville, Md.-based company that provides operational support for clinical and biomedical research.

Researchers found obese children generally got their transplants at an earlier age, 8.9 years versus 11 years; spent more time on dialysis than their leaner peers and were more frequent users of peritoneal dialysis, which takes place within the body. With peritoneal dialysis, patients put a sugar-rich sterile solution called dialysate into their abdominal cavity through a catheter. The dialysate pulls waste and excess fluid from the blood, which is drained from the abdomen. Although some say this approach is more natural than hemodialysis, where patients spend several hours typically three days a week hooked up to a machine that removes their blood, cleans it and returns it to them, the sugar-rich dialysate provides a lot of calories and can help contribute to obesity, Dr. Hanevold says.

Children who develop kidney failure at a young age have difficulty gaining height and weight and, ironically, nutritional supplements some children are given to help them grow normally may contribute to obesity as well, she says. "If you don't get renal failure until you are older, then you usually grow to be a pretty good size before kidney failure started making it hard for you to grow tall," she says. "In the young children, we provide a lot of nutritional support, hoping to ensure normal growth, but sometimes they grow more out than up."

Perhaps even more ironically, some of the drugs required to avoid rejecting a transplanted kidney also can contribute to obesity and other problems, Dr. Hanevold says. Prednisone, a non-specific immunosuppressive agent, typically given in conjunction with newer, more potent and specific agents such as cyclosporine, can make children ravenous, she says. Other possible side effects such as high blood pressure and diabetes contribute to concerns about the cardiovascular health of these children.

Studies are under way to try and reduce or eliminate prednisone, although results to date indicate children might have to take quite a bit more of the other immunosuppressive agents instead, which have their own side effects, Dr. Hanevold says.

To help minimize risks, she suggests parents and pediatricians make good nutrition a part of the ongoing care of children with kidney disease – and all children.

"Adolescents may already be overweight when they develop kidney disease and the little ones may develop obesity as a result of some of their therapy," she says. "We need to try and help kids, if they are heavy, to try to lose weight before they get a transplant and to pay more attention to their weight afterward."