*3.4.2 Vitamin D*

Vitamin D is a fat-soluble vitamin absorbed preferentially in the jejunum and ileum. Hence, a high incidence of vitamin D deficiency in seen after malabsorptive procedures despite routine supplementation [16]. The reported deficiency after LSG and RYGB is 66.7% and 65.4% respectively [26]. The prevalence of post BPD/ DS vitamin D deficiency ranged from 37.1% at one year to 50.8% at 6 years [29]. The most important consequence of vitamin D deficiency is bone demineralization. Therefore, despite the absence of conclusive evidence regarding the long-term risk of fractures after BS, calcium and vitamin D routine supplementation is strongly recommended, especially after RYGB and malabsorptive procedures [10, 30]. The standard supplementation is frequently insufficient to maintain adequate vitamin D levels in patients with malabsorption, and much higher oral or parenteral doses may be required [8, 28]. For treatment, vitamin D3 is recommended as it is a more potent than vitamin D2; however, both can be utilized [10].
