Vitamin D insufficiency prior to bariatric surgery: risk factors and a pilot treatment study

Abstract

Objective: To assess vitamin D status and the influences of race, sun exposure and dietary vitamin D intake on vitamin D levels, and to evaluate two vitamin D repletion regimens in extremely obese patients awaiting bariatric surgery.

Methods: A cross-sectional analysis of dietary vitamin D, sun exposure, PTH [intact (iPTH) and PTH(1-84)] and 25-hydroxyvitamin D (25OHD; differentiated 25OHD2 and 25OHD3) in 56 obese [body mass index (BMI) > 35 kg/m(2)] men and women (age 20-64 years). In a pilot clinical trial, 27 subjects with 25OHD levels < 62 nmol/l were randomized to receive ergocalciferol or cholecalciferol for 8 weeks.

Results: Serum 25OHD was low (mean 45 +/- 22 nmol/l) and was inversely associated with BMI (r = -0.36, P < 0.01). Each BMI increase of 1 kg/m(2) was associated with a 1.3 nmol/l decrease in 25OHD (P < 0.01). BMI, sun exposure, African American race and PTH predicted 40% of the variance in 25OHD (P < 0.0001). Serum 25OHD significantly increased at 4 and 8 weeks in both treatment groups (P < 0.001), whereas PTH(1-84) declined significantly in subjects treated with cholecalciferol (P < 0.007) and tended to decrease following ergocalciferol (P < 0.09).

Conclusions: In severely obese individuals, those who are African American, have higher BMI and limited sunlight exposure are at greatest risk for vitamin D insufficiency. These demographic factors can help to identify at-risk patients who require vitamin D repletion prior to bariatric surgery. Commonly prescribed doses of ergocalciferol and cholecalciferol are effective in raising 25OHD. Further investigation is needed to evaluate whether these regimens have differential effects on PTH, and to determine the optimal regimen for vitamin D repletion in the extremely obese patient.

Trial registration: ClinicalTrials.gov NCT00288873.

Fig. 1

The distribution of 25-hydroxyvitamin D (25OHD) serum concentrations in 56 extremely obese men and women.

Fig. 2

The association [Spearman correlation coefficient (r)] between 25-hydroxyvitamin D (25OHD) concentration and body mass index (BMI).

Fig. 3

The association [Spearman correlation coefficient (r)] between 25-hydroxyvitamin D3 (25OHD3) concentration and sunlight exposure (Sun Score).

Fig. 4

Changes in 25OHD2, 25OHD3, total 25OHD and PTH with cholecalciferol (D3) and ergocalciferol (D2) treatment.