Obesity Linked To Hyperparathyroidism In Chronic Kidney Disease

"We knew that in people with normal kidney function obesity leads to impairment in vitamin D metabolism and elevated PTH levels, but this phenomenon was never studied in patients with CKD," comments lead author Dr Csaba P. Kovesdy, of Salem VA Medical Center, in Salem, Va. "Since both obesity and hyperparathyroidism are very complex problems in CKD, establishing an association between the two is important because of potential prognostic and therapeutic implications."

The study was based on a database of 496 U.S. veterans with moderate to severe CKD who were not yet on dialysis. The database allowed the researchers to test the association between body weight and PTH levels, while accounting for a number of possible confounding factors.

The results showed a significant association between obesity and hyperparathyroidism—as body mass index increased, so did PTH levels. The relationship between increased PTH and body weight was unaffected by age, race, diabetes, or other factors.

A further analysis was done to determine if the association was present in all patients with CKD or just certain subgroups. "Interestingly, we found that obesity was only associated with higher PTH levels in patients who also showed signs of malnutrition and inflammation," says Dr. Kovesdy. "This finding may be unique to patients with CKD. Besides providing a possible explanation for why PTH levels are higher in obese patients, it may also be important for prognostic reasons, since malnutrition and inflammation are among the major complications responsible for poor outcomes in CKD."

Parathyroid hormone plays an important role in maintaining normal bone structure. When hyperparathyroidism develops, it can lead not only to bone abnormalities but also to increased rates of cardiovascular disease and death. Although decreased kidney function is the main reason for hyperparathyroidism in CKD, other factors can also affect PTH levels. Dr. Kovesdy explains, "Our current therapeutic practices aimed at correcting elevations in PTH focus mainly on abnormalities created by the decreased kidney function, and don't factor in these other mechanisms."

The study is the first to show that a higher body mass index is associated with higher parathyroid hormone levels in CKD. The results raise the possibility that weight loss might help to lower PTH levels in patients with CKD—or, conversely, that other treatments for hyperparathyroidism could lead to weight loss.

"We hope the findings will trigger further studies in order to better explain the reasons underlying our results, and to determine if the association between obesity and hyperparathyroidism has implications for the treatment or outcomes of CKD," Dr. Kovesdy concludes.

The study entitled, “Obesity is Associated with Secondary Hyperparathyroidism in Men with Moderate and Severe Chronic Kidney Disease” will be available online at http://www.asn-online.org under Media, 2007, beginning on Wednesday, August 8 at 8:00 PM and in print in the September issue of the Clinical Journal of the American Society of Nephrology (CJASN).

The ASN is a not-for-profit organization of 10,000 physicians and scientists dedicated to the study of nephrology and committed to providing a forum for the promulgation of information regarding the latest research and clinical findings on kidney diseases.