By John Gever, Staff Writer, MedPage Today
Published: September 23, 2008
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco
Markers of bone turnover increased and bone mineral density at the femoral neck and total hip declined by 9.2% and 8% (P<0.005 for both), respectively, in 23 patients evaluated a year after Roux-en-Y bypass surgery, reported Shonni J. Silverberg, M.D., of Columbia University, and colleagues online in the Journal of Clinical Endocrinology and Metabolism.
In addition, parathyroid hormone levels rose about 15% in the first three months, urinary calcium excretion declined from 161 to 92 mg/hour despite doubled calcium intake, and serum levels of vitamin D remained nearly constant even though intake more than tripled.
These signs of poor nutrient absorption were not present prior to surgery, the researchers said.
Dr. Silverberg and colleagues concluded that gastric bypass surgery was responsible for them and the consequent loss of bone mineral content.
“A high degree of vigilance for nutritional deficiencies and bone loss in patients both before and after bariatric surgery is crucial,” they wrote.
The researchers also found that loss of bone mineral content was strongly associated with the degree of weight loss, with correlation coefficients of 0.90 at the femoral neck (P<0.0001) and 0.65 for the total hip (P=0.02).
Although earlier research on patients following gastric bypass had found evidence that calcium, parathyroid hormone, and vitamin D metabolism are abnormal, those studies had not ruled out their presence prior to surgery, the researchers said.
In addition, the current findings are the first to show a linear relationship between weight loss and declining bone mineral density.
The findings emerged from a prospective analysis of the 23 patients undergoing Roux-en-Y bypass surgery at a hospital affiliated with Columbia.
Mean body mass index and weight of patients at baseline were 47 (SD 1.3) and 130.7 kg (SD 5.4), respectively.
After three months, BMI and weight declined to 38.6 (SD 1.2) and 108.4 kg (SD 4.3), respectively. Further declines to 30.8 (SD 1.0) and 85.9 kg (SD 4.3) were recorded at one year after surgery, respectively.
Dr. Silverberg and colleagues found that urine levels of N-telopeptide of type I collagen and serum osteocalcin — markers of bone turnover — increased significantly from baseline to the one-year evaluation.
N-telopeptide levels rose 106% and osteocalcin increased by 39% (P<0.01 for both).
Bone mineral density at the lumbar spine and distal radius did not change significantly during the study period. Similar findings have been reported in some but not all previous studies of bariatric surgery patients.
The researchers said the anabolic effect of increased parathyroid hormone might preferentially benefit the lumbar spine because of its unique structure.
They said the bone loss at the hip could result at least partly from the reduced weight load.
The suggestion is in line with another recent study, which found loss of bone mass in patients who lost weight through dieting, though not to an unhealthy degree. (See: Bone Health Preserved Despite Rapid Weight Loss).
Dr. Silverberg and colleagues said their measurements of bone density might not be fully reliable, as previous studies have shown that dual-energy x-ray absorptiometry can give anomalous results in people with large changes in body composition.
They said the lack of a control group was also a limitation to the study.
“The small sample size of this study argues for larger, long-term studies to answer the critical question of how these losses relate to bone quality and fracture risk,” the researchers added.
Once again, TAKE YOUR VITAMINS!