Nutritional status prior to and during pregnancy influences growth and development of the foetus and general maternal health.
The incidence of maternal obesity is increasing worldwide, across Europe and in the United Kingdom. Yet studies examining micronutrient intakes during pregnancy have tended to focus on under-nourished women, rather than those with obesity.
Women with obesity are often considered to be ‘over-nourished’ however, a recent observational study conducted in England reported that intakes of iron, vitamin D, iodine and folate were below the reference nutrient intake (RNI) for the majority of women with obesity.
Folate and folic acid play an important role in the prevention of neural tube defects (NTDs). The neural tube closes within four weeks of conception, and thus, the Department of Health in the UK recommend that women supplement with 400 µg folic acid daily from pre-conception to 12 weeks gestation.
However, maternal obesity has been shown to be associated with increased risk of NTDs and in the US, despite implementation of the 1998 US folate fortification program of cereal products, increased maternal BMI was associated with lower serum folate status.
In the UK, the Royal College of Obstetricians and Gynaecologists (RCOG) recommend that women with obesity (body mass index (BMI) ≥ 30 kg/m2) should take a higher dose of 5 mg folic acid daily.
In addition to folate, vitamin D and iodine are important micronutrients during pregnancy for foetal brain and skeletal development.
The recent observational study, conducted in Plymouth, UK, concerned the collection of weight gain, diet, physical activity, sleep and infant data amongst a cohort of pregnant women with obesity. The aim was to examine the dietary and supplementary intakes of key nutrients of interest in this population: folate, iodine and vitamin D and to investigate for any association between supplement use and key maternal demographic characteristics.
The study revealed that folic acid was taken by 96% of women at any point in the first trimester, but only 26% of women took the higher 5 mg dose recommended for women with obesity in the UK. And for vitamin D and iodine, just 56% and 44% of women met the UK RNI, respectively.
The study is unique in that it focuses on supplementation trends for three key micronutrients of concern amongst pregnant women with obesity.
"We hope that our findings will be of use to health professionals involved in the dietary counselling of women pre-conception and in early pregnancy, and that we will highlight groups of women for whom interventions promoting supplementation may have the most impact," conclude the authors.
Pregnant women aged between 18 and 40 years were recruited at Derriford Hospital in Plymouth, UK, between January 2015 and December 2017.
At 12 and 14 weeks gestation participants answered a baseline questionnaire which asked about demographic characteristics as well as preconception supplementation habits. Participants were also given a food diary and asked to record, in as much detail as possible, all food and beverages consumed within four days following each study visit. Subjects were also asked to record any dietary supplements.
Findings from this observational study demonstrate that whilst 46% and 96% of pregnant women with obesity took a folic acid supplement pre-conception and in the first trimester, respectively, only 26% of women took the higher 5 mg dose recommended by the RCOG. For vitamin D and iodine, 56% and 52% of women met the UK RNI, respectively.
For women who did not supplement with these two micronutrients, no women met the RNI for vitamin D and only 16% of women met the RNI for iodine. Maternal age was positively associated with taking supplements of any kind and taking the 5 mg folic acid supplement, whilst parity was inversely associated with both outcomes.
Of the women not supplementing with iodine in the present study, only 6 women (16%) met the RNI from dietary intakes, which the authors say give possible cause for concern as iodine supplements are not currently recommended in the UK, and unlike vitamin D and folic acid, iodine is not included in the NHS Healthy Start vitamins that are available free of charge to low-income women in the UK. The majority of other branded multivitamin products marketed to pregnant women in the UK that are sold in supermarkets and high street pharmacies do contain iodine.
A limitation of this study is that women were all of white Caucasian origin, so we were not able to examine whether race or ethnicity predict supplement use in women with obesity. The authors also acknowledge that based on the mean reported energy intake of 1766 ± 442.6 kcal/day, it is possible and likely that some women under-reported their dietary intake, which may have led to under-estimations of dietary intakes of micronutrients.
The researchers conclude: "In the UK, the 5 mg folic acid supplement is only available on prescription, so it is imperative that GPs and midwives are aware of the higher dose recommendations for women with obesity and counsel women prior to conception if possible.
"This is particularly important for low-income women who may be eligible for free NHS Healthy Start vitamins, which contain the 400 µg folic acid rather than the higher 5 mg dose. Further research is required to investigate iodine status and whether there is potential for iodine supplementation in pregnancy to improve pregnancy and infant outcomes."
2022, 14(23), 5135; https://doi.org/10.3390/nu14235135 (registering DOI)
"Dietary Intakes of Folate, Vitamin D and Iodine during the First Trimester of Pregnancy and the Association between Supplement Use and Demographic Characteristics amongst White Caucasian Women Living with Obesity in the UK"
Redfern, K.M.; Hollands, H.J.; Welch, C.R.; Pinkney, J.H.; Rees, G.A.