The mediating role of bariatric surgery in the metabolic relationship between parathyroid hormone and 25-hydroxyvitamin D

Dynamic Evaluation of Vitamin D Metabolism in Post-Bariatric Patients

BACKGROUND

findings from the previously conducted studies indicate altered regulatory mechanisms of calcium and vitamin D metabolism in obese patients and a role for bariatric surgery in regulating vitamin D metabolism; however, the available data is controversial and does not provide an adequate understanding of the subject.

METHODS

we evaluated serum parameters of vitamin D and mineral metabolism (vitamin D metabolites (25(OH)D3, 25(OH)D2, 1,25(OH)2D3, 3-epi-25(OH)D3, and 24,25(OH)2D3), vitamin D-binding protein (DBP), free 25(OH)D, fibroblast growth factor 23 (FGF-23), parathyroid hormone (PTH), total calcium, albumin, phosphorus, creatinine, magnesium) in 30 patients referred for bariatric surgery in comparison with 30 healthy volunteers of similar age, sex and baseline 25(OH)D3. Patients were also followed up with repeated laboratory assessments 3 months and 6 months after surgery. During the first 3 months, patients were prescribed high-dose cholecalciferol therapy (50,000 IU per week), with subsequent correction based on the results of the 3-month visit examination.

RESULTS

Preoperatively, patients with morbid obesity were characterized by a high prevalence of vitamin D deficiency (median 25(OH)D3 level 11.9 (6.8; 22.2) ng/mL), significantly lower levels of active vitamin D metabolite 1,25(OH)2D3 (20 (10; 37) vs. 39 (33; 50) pg/mL, p < 0.001), lower serum albumin-adjusted calcium levels (2.24 (2.20; 2.32) vs. 2.31 (2.25; 2.35) mmol/L, p = 0.009) and magnesium levels (0.79 (0.72; 0.82) vs. 0.82 (0.78; 0.85) mmol/L, p = 0.043) with simultaneous similar PTH levels (p = 0.912), and higher DBP levels (328 (288; 401) vs. 248 (217; 284) mg/L, p < 0.001). The 25(OH)D3 levels remained suboptimal (24.5 (14.7; 29.5) ng/mL at the 3-month visit and 17.9 (12.4; 21.0) ng/mL at the 6-month visit, p = 0.052) despite recommended high-dose cholecalciferol supplementation. Patients also demonstrated an increase in 1,25(OH)2D3 levels (38 (31; 52) pg/mL at the 3-month visit and 49 (29; 59) pg/mL at the 6-month visit, p < 0.001) without a change in PTH or calcium levels during the follow-up.

CONCLUSION

our results of a comprehensive laboratory evaluation of vitamin D status and mineral metabolism in patients undergoing bariatric surgery highlight the importance of improving current clinical guidelines, as well as careful monitoring and education of patients.

Long-term trajectories of bone metabolism parameters and bone mineral density (BMD) in obese patients treated with metabolic surgery: a real-world, retrospective study

PURPOSE

Potential negative effects of metabolic surgery on skeletal integrity remain a concern, since long-term data of different surgical approaches are poor. This study aimed to describe changes in bone metabolism in subjects with obesity undergoing both Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG).

METHODS

A single center, retrospective, observational clinical study on real-world data was performed enrolling subjects undergoing metabolic surgery.

RESULTS

123 subjects were enrolled (males 31: females 92; ages 48.2 ± 7.9 years). All patients were evaluated until 16.9 ± 8.1 months after surgery, while a small group was evaluated up to 4.5 years. All patients were treated after surgery with calcium and vitamin D integration. Both calcium and phosphate serum levels significantly increased after metabolic surgery and remained stable during follow-up. These trends did not differ between RYGB and SG (p = 0.245). Ca/P ratio decreased after surgery compared to baseline (p < 0.001) and this decrease remained among follow-up visits. While 24-h urinary calcium remained stable across all visits, 24-h urinary phosphate showed lower levels after surgery (p = 0.014), also according to surgery technique. Parathyroid hormone decreased (p < 0.001) and both vitamin D (p < 0.001) and C-terminal telopeptide of type I collagen (p = 0.001) increased after surgery.

CONCLUSION

We demonstrated that calcium and phosphorous metabolism shows slight modification even after several years since metabolic surgery, irrespective of calcium and vitamin D supplementation. This different set point is characterized by a phosphate serum levels increase, together with a persistent bone loss, suggesting that supplementation alone may not ensure the maintenance of bone health in these patients.

Changes in Bone Turnover Markers after Roux-en-Y Gastric Bypass Versus Sleeve Gastrectomy: a Systematic Review and Meta-Analysis

This systematic review and meta-analysis was performed to compare the alterations in bone turnover markers between SG and RYGB. A literature search was conducted in PubMed, Medline, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL) databases to find the studies. There was significant less increment in osteocalcin [WMD =  - 5.98, 95% CI (- 9.30, - 2.47) P < 0.01] and parathyroid hormone (PTH) [WMD =  - 9.59, 95% CI (- 15.02, - 4.16) P < 0.01] in the SG group compared to the RYGB group. No significant differences were seen in change of C-terminal telopeptide of type I collagen (CTX), N-terminal propeptide of type I collagen (PINP), Ca, and 25(OH)-D between SG and RYGB groups. According to our meta-analysis, bone formation markers appear to have more increment following RYGB than SG. This observation is accompanied by a larger increase in PTH after RYGB patients compared to SG patients. PROSPERO: CRD42022308985.

Determinants of Secondary Hyperparathyroidism 1 Year After One-Anastomosis Gastric Bypass or Sleeve Gastrectomy

PURPOSE

Bariatric surgery alters the anatomic and physiological structure of the gastrointestinal tract, predisposing patients to the malabsorption of nutrients. The purpose of this study was to determine the prevalence and determinants of secondary hyperparathyroidism (SHPT) in the patients undergoing either one-anastomosis gastric bypass (OAGB) or sleeve gastrectomy (SG).

MATERIALS AND METHODS

A total of 517 patients (without SHPT at the baseline) who had undergone OAGB or SG were prospectively assessed 1 year after the surgery. Anthropometric parameters, calcium, intact parathyroid hormone (iPTH), and 25(OH)D levels were compared according to the surgery type before and 1 year after surgery. Multiple logistic regression models were used to evaluate possible SHPT predictors after bariatric surgery.

RESULTS

The overall prevalence of SHPT was 12.6% after surgery, significantly different between the OAGB and SG groups (17.1 vs. 9.9%, respectively). The serum levels of albumin-corrected calcium and 25(OH)D were not significantly different between the two groups. The patients undergoing OAGB had significantly higher serum levels of ALP (198.2 vs. 156.6) compared to the subjects undergoing SG. Higher iPTH levels preoperatively, lower 1-year excess weight loss%, and OAGB surgery seemed to be independent predictors for SHPT 1 year after surgery.

CONCLUSION

Morbidly-obese patients undergoing OAGB had a higher risk of SHPT than their counterparts undergoing SG, whereas 25(OH)D deficiency and calcium levels did not differ between the two groups. The OAGB procedure, preoperative iPTH levels, and 1-year weight loss were predictors of postoperative SHPT development.