For patients with chronic kidney disease ( CKD ), the risk of elevated levels of parathyroid hormone ( PTH ), or hyperparathyroidism, increases along with body weight.

" 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 chronic kidney disease, " comments lead author Csaba P. Kovesdy, of Salem VA Medical Center, " Since both obesity and hyperparathyroidism are very complex problems in chronic kidney disease, 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 chronic kidney disease 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. 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 chronic kidney disease 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 Kovesdy. " This finding may be unique to patients with chronic kidney disease. 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 chronic kidney disease."

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 chronic kidney disease, other factors can also affect PTH levels.

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

Source: Journal of American Society of Nephrology, 2007

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