Existing research shows an association between physical activity levels and vitamin D status in the elderly, men, women, children, and adolescent populations. This association has not yet been investigated in postpartum women. We hypothesized that based on the relationship between vitamin D and physical activity found in other populations, greater physical activity levels in postpartum women will be associated with higher serum 25(OH)D levels. A post hoc analysis of 286 postpartum women with self reported physical activity data from the America on the Move survey, and measured circulating serum 25(OH)D (measured by RIA) as an indicator of vitamin D status, was gathered at baseline (4-6 weeks postpartum), 4 months, and 7 months postpartum. The data were analyzed using SAS 9.4 (Cary, NC). 39.9% of women at visit 1 (baseline), 52.8% of women at visit 4 (month 4), and 55.9% of women at visit 7 (month 7) were meeting the NIH recommendation of 150min of moderate intensity (3-6 METs) physical activity per week. Significant differences were seen in physical activity by race (p=0.007). Caucasians were more likely to meet the standard recommendation than African Americans or Hispanics. Using multiple regression models to examine associations between duration of physical activity and 25(OH)D concentration, controlling for race, BMI, feeding type, and METs, it was found that at visit 1, an increase in physical activity was associated with an increase in 25(OH)D of 1.3nmol/L (p=0.03) and achieving at least 2.5h/wk of physical activity had a trending association with an increase in 25(OH)D of 7.23nmol/L (p=.05). At visit 4 (also controlling for treatment group and sun exposure) achieving at least 1.5h/wk of physical activity was associated with an increase in 25(OH)D of 11.73nmol/L (p=.04). By visit 7, no association between physical activity and maternal 25(OH)D was observed. In a repeated measures, mixed model analysis predicting maternal 25(OH)D during the study, achieving at least the recommended 150min per week of physical activity (>2.5h) was not significantly associated with vitamin D status (pNS). While no definitive conclusions can be drawn regarding precise levels of physical activity influencing 25(OH)D levels in postpartum women, the data suggest that increased activity during the first 4 months after birth is associated with improved vitamin D status. Additional research is needed because of the inconsistency seen at visit 7.
Objective: Determine the effect of physical activity on vitamin D (vitD) status in pregnant women. Design/Methods: Women who presented at 10-14 weeks' gestation participated in vitD supplementation RCT, conducted between November 2012 and June 2016, were randomized into one of two treatment groups: 400 or 4400 IU/day of vitD3. VitD status, as defined by total circulating 25(OH)D concentration, was measured monthly. Physical activity was measured monthly using the Paffenbarger Questionnaire, and responses were categorized as vigorously exercising for ≥ 2.5 h/week during each trimester. Sunlight exposure was measured using skin spectrophotometry (SmartProbe 400). Linear regression and mixed models explored the association of maternal 25(OH)D concentration, sunlight exposure, physical activity, race, treatment group, body mass index, perceived stress score, and visit using SAS software (version 9.4). Results: 211 pregnant women had physical activity information available. At baseline, vigorously exercising ≥ 2.5 h/week was associated with being older (p=0.0004), white/Caucasian (p=0.011), privately insured (p=0.018), and purposefully pregnant (p<0.031). Baseline 25(OH)D did not vary by treatment or exercise groups. In bivariate analysis, at second trimester, vigorously exercising ≥ 2.5 h/week was associated with being white/Caucasian, privately insured, purposefully pregnant, married and with higher 25(OH)D concentration. By third trimester, vigorous exercise was associated with being privately insured, married, gravidity, sunlight exposure and Hispanic. The effect of increased exercise on 25(OH)D concentration was seen only in the 400 IU group at third trimester. In a mixed model controlling for multiple potential confounders, maternal vitD status and exercise were positively associated (p=0.018). Conclusion: Independent of sunlight exposure, pregnant women who vigorously exercised ≥ 2.5 h/week had higher 25(OH)D concentrations than those who did not. Supplementation may have overshadowed the exercise effect; the positive correlation was amplified when looking at the 400 IU group alone, and may suggest that exercise was more critical for those lacking the higher supplementation dose.
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