Vitamin D Status and Its Determinants in Mexican Pregnant Women from a Rural and an Urban Area: A Comparative Study

BACKGROUND

During pregnancy, vitamin D requirements are higher due to fetal growth and development. Vitamin D production occurs mainly through sunlight exposure, which is affected by geographic location and lifestyle factors.

METHODS

This was a case-control study nested within two cohorts of adult pregnant women (n = 298): urban (Mexico City) and rural (Cuetzalan). To reduce confounding, pairs were selected by age, pregestational body mass index, and pregnancy trimester. Generalized linear models were used to assess the two groups according to their vitamin D status.

RESULTS

A total of 298 adult women were studied: 149 from a rural area and 149 from an urban area. Vitamin D deficiency and insufficiency were observed in 28% and 38.2% of women, respectively. A trend for higher 25(OH)D concentrations was observed in women from the rural area (27.5 ng/mL vs. 25.8 ng/mL), probably related to the type of job, where women with partial jobs showing less probability of having vitamin D deficiency (OR = 0.26; CI = 0.06-1.16; p = 0.08) and vitamin D insufficiency (OR = 0.24; CI = 0.06-0.99; p = 0.05). Women whose Last Menstrual Period occurred in spring showed lower vitamin D concentration compared to those whose LMP occurred in winter (p < 0.01).

CONCLUSIONS

A high prevalence of vitamin D deficiency was observed in both rural and urban areas. Women living in rural areas tended to have higher 25(OH)D concentrations, probably related to more sunlight exposure associated with their type of job.

Vitamin D Deficiency in Mexican Pregnant Women: Is Supplementation with ≤400 IU/day Enough?

Controversy remains surrounding vitamin D routine supplementation in healthy pregnancy, and the doses are unclear. The aim of this study was to describe maternal vitamin D status throughout pregnancy in a group of Mexican women and evaluate the effect of frequently prescribed doses of vitamin D3 on longitudinal 25-OH-D concentrations, adjusting for obesity, season, and other factors. We conducted a cohort study (Instituto Nacional de Perinatología-INPer) (2017-2020)) of healthy pregnant women without complications. Pregestational overweight/obesity (body mass index ≥ 25), vitamin D3 supplementation (prescribed by physician; 0-250, 250-400, and >400 IU/day), and serum 25-OH-D concentrations (ELISA) were evaluated in each trimester of pregnancy. Vitamin D deficiency or insufficiency was computed (<20 and <30 ng/mL, respectively). We studied 141 adult women; 58.5% had pregestational obesity or overweight. In the first trimester, 45.8% of the women were supplemented with vitamin D3; 51.4% had vitamin D insufficiency and 37.3%, deficiency. In the third trimester, 75.4% of the women were supplemented, and 20% of them still had deficiency. The final general mixed linear model showed that 25-OH-D significantly increased throughout pregnancy (p < 0.001); the highest increase was observed in the third trimester in women with doses >400 IU/day of vitamin D3 (+4 ng/mL, 95% CI: 1.72-8.11 ng/mL). In winter/autumn, 25-OH-D concentrations were also lower (p ≤ 0.05). In this group of pregnant Mexican women, the prevalence of vitamin D deficiency and insufficiency was high. A higher increase in 25-OH-D concentrations during pregnancy was observed when the women were supplemented with >400 IU/day. Common supplementation doses of 250-400 IU/day were insufficient for achieving an adequate maternal vitamin D status.