The preoperative micronutrient repletion gap: high prevalence yet the focus is on postoperative treatment - a systematic review

Background:
Preoperative micronutrient deficiencies are highly prevalent for people undergoing metabolic and bariatric surgery (MBS), but research has focused on postoperative treatments.

Objective:
To determine the effect of preoperative micronutrient repletion strategies on preoperative and early postoperative micronutrient status.

Methods:
A systematic review searched four databases for studies published to April 2022 and updated in PubMed in November 2023. Interventional and observational studies were eligible if they identified and treated any micronutrient deficiency prior to MBS, except vitamin D (investigated separately). Outcomes were change in micronutrient levels and deficiency rates. Studies were critically appraised via the Quality Criteria Checklist. Findings were synthesised narratively. Confidence in the evidence was evaluated by GRADE when two or more comparable interventions reported on a primary outcome.

Results:
Sixteen repletion groups from 12 observational (100% neutral quality) and one interventional study (positive quality) were included. Repletion was delivered via oral multivitamin, oral supplement, and combined multivitamin and oral supplement (n=13 groups), intravenous (n=1 group), and a mix of oral and/or intramuscular routes (n=2 groups) with highly heterogenous doses and repletion durations.

It showed no change on status of vitamin A (n=3 out of 3 groups), vitamin E (n=2/2 groups), thiamin (n=3/3 groups), vitamin B12 (n=3/3 groups, GRADE: very low), or zinc (n=1/1 group) via oral route; no change on vitamin B12 deficiency rate via intramuscular route (n=1/1 group). Multivitamin or combined multivitamin and oral supplement improved status of vitamin B6 (n=1/2 groups), folate (n=2/3 groups), and vitamin C (n=1/2 groups) but had on change on ferritin levels (n=3/3 groups) or calcium status (n=2/2 groups). Oral supplement improved folate deficiency rate (n=1/1 group) and calcium level (n=2/2 groups) but did not change ferritin level or deficiency rate (n=2/2 groups). Intravenous iron infusion improved ferritin levels (n=1/1 group).

Conclusion:
Preoperative micronutrient repletion strategies were heterogeneous and varied in effectiveness, limiting confidence in the evidence. Oral supplements may support repletion of vitamin B6, folate, vitamin C, and calcium; and iron infusion may improve ferritin levels. Future studies using interventional design are required to confirm ideal repletion strategies for clinical efficacy, safety, and feasibility.