**5.3 Metabolic bone disease**

The bone mineral density rapidly decreases initially after BS, which reflects a skeletal adaptation to a lower body weight. Bone loss however, continues even after weight loss has stopped [52]. This is likely due to the lower calcium absorption and vitamin D deficiency causing secondary hyperparathyroidism [53]. The prevalence of secondary hyperparathyroidism has been shown to increase progressively with time from 35.4% at 1 year after BS to 63.3% at 5 years after surgery [54]. Patients who underwent a single anastomosis gastric bypass had the highest prevalence of secondary hyperparathyroidism (73.6%) followed by RYGB (56.6%), gastric banding (38.5%), and sleeve gastrectomy (41.7%) at 5 years after surgery [54]. The decrease in bone density may predispose patients to the risk of fractures especially with malabsorptive procedures. However, data on the incidence of fractures post BS remain controversial, with some studies suggesting an increased risk of fractures (non-vertebral fractures, especially in the upper limbs) and others showing no increased risk [55–57]. For instance, one study reported a significantly increased number of fractures only after biliopancreatic diversion (adjusted relative risk 1·60, 95% CI 1·25–2·03; p < 0·001, 56]. Others found that 60% of LAGB and 29% of RYGB patients had increased risk of fractures 3–4 years after surgery [55]. Future long-term studies are required to assess the effect of BS on bone health.

Evaluation of patients for metabolic bone disease after BS may include serum parathyroid hormone, total calcium, phosphorus, 25-hydroxyvitamin D, and

*Nutritional Deficiencies Post Bariatric Surgery: A Forgotten Area Impacting Long-Term Success... DOI: http://dx.doi.org/10.5772/intechopen.95123*

24-hour urine calcium levels [10]. In post-bariatric patients with established osteoporosis, pharmacologic treatment with bisphosphonates may be considered. Before starting bisphosphonate treatment, vitamin D deficiency needs to be fully corrected in order to avoid severe hypocalcaemia, hypophosphatemia, and osteomalacia. In these cases, intravenous form of bisphosphonates should be used (zoledronic acid, 5 mg once a year, or ibandronate, 3 mg every 3 months) for better absorption and to avoid potential anastomotic ulceration with orally administered bisphosphonates [10]. More research is needed to examine the effectiveness of both intravenous and oral bisphosphonates in improving bone mineralization [15].
