Study finds post-RYGB low bone mineral density is procedure-related
Compared to controls, Roux-en-Y gastric bypass (RYGB) patients had lower bone mineral density (BMD) despite reporting higher skeletal strain and indicating a more calcium rich diet, supporting the theory that BMD reduction is procedure-related, according to a study by researchers from University Hospital, Uppsala, Sweden. Therefore, the researchers concluded that the reduced BMD in RYGB patients cannot be explained by lifestyle factors and they caution that strict follow-up is a lifelong necessity after bariatric surgery, and especially important in younger bariatric patients. The findings were featured in the paper, ‘Low bone mineral density following gastric bypass is not explained by lifestyle and lack of exercise’, was published in BMC Surgery.
The authors noted that several studies have reported that BMD is reduced in patients after bariatric surgery, although there is a paucity of studies that have examined the impact lifestyle factors may have upon BMD in RYGB patients. Furthermore, additional research has identified that a significant number of bariatric surgery patients have a calcium deficiency after two years. Therefore, the researchers designed a study to compare the lifestyle factors in two groups of premenopausal women: RYGBP-operated and controls.
In total, 165 females were included in the study, 71 participants in the RYGBP group and 94 in the control group. All participants had a bone mineral density (DEXA) scan of the femoral neck, total hip, and lumbar spine (vertebrae L1–L4), and completed a survey about their lifestyle factors. The lifestyle survey included questions about:
health related events (smoking, fractures, menarche, and current medications)
physical activity, and;
Patients who had RYGB gave details about the duration of their obesity, preoperative weight and date of surgery.
Th researchers identified that there were no differences in calcium intake or in physical activity between the two groups at baseline (five years ago) and the latest follow-up. DEXA results showed that BMD of the femoral neck and total hip was significantly lower in RYGB-patients vs controls, 0.98 vs. 1.04g/cm2 and 1.02 vs 1.07g/cm2, respectively. However, no differences were seen in BMD Spine (1.22 vs. 1.24g/cm2). There was a significant correlation between BMI and BMD of the total hip in the control group, which is not seen in the RYGBP group (p=0.214).
The RYGBP group achieved a mean weight loss of 34.4 kg (BMI 45.4 to 33.1kg/m2), the mean age at surgery was 34.7 years and mean duration of obesity was 23.1 years. A univariate regression analysis revealed that younger age and not having undergone RYGB were associated with higher BMD of both the femoral neck and total hip. However, no associations were seen for lifestyle factors. After carrying out a multivariate analyses, there was a trend towards association between higher BMD of the femoral neck and younger age (p=0.09), as well as time since surgery (p=0.06). For BMD of the total hip, each postoperative year was associated with a reduction of BMD by 0.005 g/cm2 (p<0.05). A trend towards association between BMI at surgery and BMD of the total hip was also reported (p=0.083).
The researchers summarised that:
RYGB halts the mechanostat mechanism of bone remodelling, possibly due to malabsorption of skeletal building blocks from the intestine
Considering a significantly higher intake of calcium and identical post-surgery supplement recommendations, diet was not identified as a key cause to the lower BMD seen in the RYGBP group
Bariatric patients are at risk for reduced BMD and younger patients undergoing surgery may be especially vulnerable if peak BMD is stunted
The researchers also highlighted that despite joint guidelines released by the American Association of Clinical Endocrinologists (AACE), the Obesity Society, and American Society for Metabolic and Bariatric Surgery (ASMBS) stating that DEXA bone density scans are indicated both preoperatively and two years after bariatric surgery, these guidelines have yet to be adopted in Sweden.
“Further, BMD measurements were significantly inversely associated with postoperative time,” the researchers concluded. “From this study we conclude that current postoperative follow-up regimes need to be expanded with a more aggressive approach to screen for and prevent decreases in BMD, and essentially the development of osteopenia/osteoporosis.”
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