Nutritional Status of Obese Taiwanese Before Bariatric-Metabolic Surgery and Their Serum 25-Hydroxyvitamin D Concentrations for Maximal Suppression of Parathyroid Hormone

Background: This is the first report from Taiwan using laboratory tests to assess nutritional status of patients with obesity before bariatric-metabolic surgery. Moreover, the 25(OH)D threshold for maximal suppression of parathyroid hormone (PTH) was evaluated to offer a reference value for preoperative nutritional care.

Methods: Inclusion criteria were Taiwanese, 18-65 years old, and with BMI ≥ 27.5 kg/m² awaiting bariatric-metabolic surgery. Anthropometric data and blood samples were collected before surgery. Serum concentrations of protein; vitamins B₁, B₁₂, folate, A, D, and E; calcium; iron; zinc; copper; selenium; PTH; and erythrocyte glutathione reductase activity coefficient (vitamin B₂ status) were measured.

Results: For 52 participants with a mean BMI 37.6 ± 6.4 kg/m², vitamin D deficiency (25(OH)D < 20 ng/mL) and insufficiency (20 < 25(OH)D < 30 ng/mL) were at 73 and 22% prevalence, respectively. Secondary hyperparathyroidism (PTH ≧ 65 pg/mL) was 24% and hypocalcemia was 50% (ionized Ca < 4.5 mg/dL). Deficiency of other nutrients was sporadic (< 10%) or nil. When participants were stratified according to 25(OH)D concentrations (< 10, 10-15, 15-20, and ≥ 20 ng/mL), PTH increased at 25(OH)D < 10 ng/mL (β = 48.34, p = 0.001) after adjusting for age, gender, and BMI.

Conclusion: For patients with obesity before bariatric-metabolic surgery, vitamin D/calcium deficiency was the only nutritional issue that needs to be addressed in Taiwan. However, a lower cutoff point of 25(OH)D, i.e., 10 ng/mL, for vitamin D deficiency may be considered for patients before surgery.

Trial registration: ClinicalTrials.gov Identifier: NCT03915158.

Keywords: 25-Hydroxyvitamin D; Bariatric-metabolic surgery; Nutritional assessment; Obesity; Parathyroid hormone.