Predictors of 25-hydroxyvitamin D concentrations during pregnancy: A longitudinal analysis in the Brazilian Amazon

To determine predictors of 25-hydroxyvitamin D₃ (25(OH)D₃) concentrations (25^th, 50^th, and 75^th percentiles) in the third trimester of pregnancy.

Data on sociodemographic, obstetric, lifestyle and pregnancy characteristics, including serum 25(OH)D₃ and retinol, were collected among 448 pregnant women who participated in the Maternal and Child Health and Nutrition in Acre, Brazil (MINA-Brazil Study) in Cruzeiro do Sul, Brazilian Amazon (latitude 7°S). Simultaneous-quantile regression was fitted to prospectively assess predictors at the 25^th, 50^th and 75^th percentiles of 25(OH)D₃ concentrations.

In the third trimester, 25(OH)D₃ <50 nmol/L was observed in 26% of pregnant women. Exposure to the Amazonian dry season during follow-up and vitamin D status ≥75 nmol/L in the second trimester of pregnancy were positively associated with 25(OH)D₃ concentrations in the third trimester. Pregnant women who were the main providers of family income presented lower 25(OH)D₃ concentrations (50^th and 75^th percentiles: -15 nmol/L, 95%CI -24; -3, p = 0.02, and -22 nmol/L, 95%CI -36; -7, p = 0.004, respectively), as well as those with sustained vitamin A insufficiency (25^th and 50^th percentiles: -27 nmol/L, 95%CI -40; -15, p < 0.001, and -17 nmol/L, 95%CI -33; -1, p = 0.04, respectively). Sun protection practices had a smaller negative impact on 25(OH)D₃, restricted to participants whose concentrations were at the 25^th percentile of the distribution.

Seasonality and vitamin A status were important predictors of 25(OH)D₃ concentrations in the third trimester. Adequate exposure to sunlight and dietary sources of vitamin A within safe intake levels may help ensuring a good nutritional status of vitamin D during pregnancy.