Effectiveness of a Bariatric-Specific Multivitamin Versus Conventional Targeted Supplementation for Preoperative Micronutrient Deficiency Correction in Bariatric Surgery Candidates: A Multicenter Retrospective Cohort Study

Background: Micronutrient deficiencies (MD) are highly prevalent among candidates for bariatric surgery (BS) and are associated with adverse perioperative and postoperative outcomes. Although guidelines recommend systematic preoperative screening and correction, conventional targeted supplementation (CTS) often requires multiple products, potentially limiting adherence and delaying surgical readiness. Bariatric-specific multivitamins (BSM) may simplify nutritional management, but their real-world effectiveness for preoperative correction of multiple MD remains insufficiently investigated. Objective: To compare the effectiveness, efficiency, and adherence of a BSM versus CTS for preoperative correction of multiple MD in BS candidates. Methods: This retrospective multicenter cohort study included 1560 adults with obesity evaluated for BS between 2020 and 2024 across three Italian bariatric centers. The primary efficacy analysis was restricted to patients presenting with ≥3 laboratory-confirmed MD at baseline. Patients treated between 2020 and 2022 received individualized CTS using multiple products, whereas those treated between 2023 and 2024 received a single BSM. Biochemical follow-up was scheduled at 4 and 8 weeks. The primary outcome was the achievement of complete biochemical correction of all baseline deficiencies at the predefined 4-week follow-up assessment (composite endpoint). Secondary outcomes included supplementation burden and self-reported adherence. Early correction rates were compared using absolute risk differences and risk ratios; adjusted associations were evaluated using multivariable regression models including center and baseline deficiency burden. As a supplementary analysis, the patient-level proportion of baseline deficiencies corrected at 4 weeks was also evaluated. Results: Among patients with ≥3 baseline deficiencies (n = 216), complete biochemical correction at 4 weeks was achieved in 55/134 patients (41.0%) in the BSM group and in 13/82 patients (15.9%) in the CTS group, corresponding to an absolute risk difference of 25.2 percentage points (95% CI 7.8–40.0) and a risk ratio of 2.59 (95% CI 1.51–4.44). In adjusted analyses accounting for center and baseline deficiency pattern, BSM use remained independently associated with early complete correction (adjusted absolute risk difference 26.3 percentage points; adjusted risk ratio 2.69). Sensitivity analyses restricting follow-up timing and excluding early calendar periods yielded consistent results. The mean proportion of baseline deficiencies corrected per patient at 4 weeks was higher in the BSM group compared with CTS (0.74 ± 0.25 vs. 0.54 ± 0.30). Compared with CTS, BSM was associated with lower supplementation burden (1 vs. 3.5 supplements on average) and higher adherence (92% vs. 70%). Conclusions: In a real-world multicenter cohort of BS candidates with ≥3 baseline MD, a simplified preoperative supplementation strategy based on a BSM was associated with a significantly higher probability of complete biochemical correction at 4 weeks, lower supplementation burden, and higher reported adherence compared with CTS. Although complete correction was not universal at 4 weeks, BSM significantly increased the likelihood of achieving early multi-deficiency normalization. Given the non-concurrent observational design, these findings should be interpreted as hypothesis-generating and warrant confirmation in prospective studies with concurrent cohorts.