Gave 1,000 IU of Vitamin D daily while pregnant (no surprise, no benefit) - RCT
Process evaluation of a randomised controlled trial aimed at improving health behaviours and vitamin D status during pregnancy: Implementation of the SPRING trial
PLoS One. 2025 Sep 15;20(9):e0319224. doi: 10.1371/journal.pone.0319224
Simone Proebstl 1 2 3, Christina Vogel 3 4 5 6, Wendy Lawrence 7, Sofia Strömmer 3, Hazel Inskip 3 4, Julia Hammond 3, Kate Hart 3, Karen McGill 3, Nicholas C Harvey 3 4, Mary Barker 3 4 8, Janis Baird 3 4
Background: The Southampton PRegnancy Intervention for the Next Generation (SPRING) aimed to assess the efficacy of vitamin D supplementation and the behaviour change intervention 'Healthy Conversation Skills' (HCS) in improving the nutritional status of pregnant women. This paper describes the implementation of these interventions. Efficacy of HCS in improving diet quality and physical activity was evaluated in subgroups of women who discussed ways to improve these behaviours.
Methods: In total, 717 pregnant women were recruited from a maternity hospital in Southampton, England. Quantitative data were collected using questionnaires, case report forms, and audio recordings. Following Medical Research Council guidance, fidelity, dose, and reach were evaluated descriptively. Multiple linear regression models were produced for subgroup analyses.
Results: Research nurses demonstrated high competence in using HCS. Compliance with intervention protocols for delivering and receiving both interventions was high. Participants took a median of 96% of the supplements and most women (85%) attended all four Healthy Conversations sessions. Women of lower socioeconomic status and from ethnic minorities were under-represented amongst participants. Findings were not sufficient to suggest an effect of HCS on diet quality among those who discussed diet but indicated a marginally beneficial effect on physical activity among those who discussed physical activity. Results suggested a weak dose-dependent effect, with the most pronounced difference in physical activity between the control group and the intervention sub-group with the highest exposure (adjusted difference 0.16 SD (95%-CI -0.03; 0.34)).
Conclusion: This process evaluation confirms that the intervention components were delivered with high fidelity and rates of compliance. Altering dietary behaviours proved more challenging than altering physical activity behaviours. Research is needed to explore barriers to healthy eating faced by women during pregnancy and how these can be overcome. This paper also highlights the difficulty of engaging people from ethnic minorities and disadvantaged backgrounds in research.
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Related in VitaminDWiki
1,000 IU of Vitamin D while pregnant helped a little bit (4,000 IU helps a lot) – RCT Dec 2016
Adding 1,000 IU vitamin D while pregnant did not help much (no surprise) – RCT Jan 2019
Needed more than 1600 IU of vitamin D during pregnancy – RCT May 2013 which has the following chart
The benefits to mom start about 2,000 IU daily average (2000 IU costs less than $15 per year)
Substantial benefits proven for 4,000 IU taken during pregnancy (fewer complications, lower cost)
Best benefits at 6,000 IU - this much is also needed if breast feeding without supplementing the infant