Low vitamin D in overweight mothers linked to lower BMI in offspring

The findings are contradictory to previous studies​, which have found maternal Vitamin D deficiency is linked with offspring obesity. 

Childhood overweight and obesity are global health concerns, with estimates suggesting that around 5.6% of children under 5 years​, and 20.6% of children between five and nine years were affected​ in 2016. 

Maternal obesity before pregnancy increases the risk of childhood obesity​ but deficiency of certain micronutrients during pregnancy may have significant consequences on foetal development that lead to chronic diseases later in life​. Vitamin D in particular is essential for skeletal health​.

In Nordic countries, up to 28% of light-skinned pregnant women have insufficient vitamin D levels​ (<50 nmol/L), which can vary seasonally​ and has been inversely related to body size​. 

Supplementation with vitamin D during pregnancy has been suggested to reduce the risk of pre-eclampsia, gestational diabetes, and low birth weight​. 

Additionally, maternal vitamin D status during pregnancy has been associated with childhood growth and adiposity​. 

A previous study​ found that maternal 25OHD ≤75 nmol/L was associated with a higher body mass index (BMI) growth trajectory class during the first 2 years of life.

Several other studies​ have investigated the association between maternal vitamin D status during pregnancy and different outcome measures of childhood adiposity, at various ages, but according to the authors of the new study, the results are inconclusive.

Low maternal 25OHD has previously been associated​ with a higher risk of overweight in 1-year-old infants, as well as with increased adiposity at 4 and 6 years​, and higher body fat percentage at 5–6 years of age​.

The authors hypothesise however, that as pre-pregnancy BMI is associated with both childhood BMI​ and inversely associated with maternal 25OHD​, it is possible that pre-pregnancy BMI could modify the association between maternal vitamin D status and childhood BMI.

The study

The study investigated the relationship between maternal vitamin D status during pregnancy and childhood overweight.  

Data sources included a subsample from the Norwegian Mother, Father, and Child Cohort Study (MoBa sub-cohort; N = 2,744) and the Swedish GraviD cohort study (N = 891). 

Maternal 25OHD was analysed in gestational week 18 in the MoBa sub-cohort and week 10 in the GraviD cohort. 

In the MoBa sub-cohort, parents reported their child’s documented measures of weight and length or height from the health card at routine check-ups.

In the GraviD cohort, information was collected directly from medical records. Childhood overweight (including obesity) was identified using the International Obesity Task Force cut-offs​. 

Linear and logistic regression models were used to investigate the association between maternal 25OHD and a child’s BMI and risk of being overweight at 5 years of age in each cohort separately and in a pooled dataset.

In the pooled analysis, maternal 25OHD <30 nmol/L was associated with lower BMI in children at 5 years of age, but not with risk of overweight. 

Interaction analysis showed that the association was predominant among children of mothers with pre-pregnancy BMI ≥25 kg/m2.

Further notes​

The authors note that the association between lower maternal vitamin D status and lower child BMI at 5 years of age was only found in children of mothers with pre-pregnancy overweight or obesity.

In concordance with these results, one Greek study​ reported maternal pre-pregnancy BMI to be an vitamin D effect modifier.

The authors hypothesise: “This finding could be that women with pre-pregnancy obesity and 25OHD concentration < 30 nmol/L might differ from those with pre-pregnancy obesity and 25OHD concentration > 75 nmol/L in terms of nutrition status, weight status, and/or gestational weight gain. 

“In addition, both the reference maternal vitamin D category (>75 nmol/L) and the category where the association was found (<30 nmol/L) contain few women among those with pre-pregnancy overweight or obesity. The results might also be explained by residual confounding.”

Discussing the differing results of studies in this space, the authors note this may be explained by the different cut offs for optimal maternal 25OHD concentration for childhood health. 

“Possibly, additional measures beyond BMI and classification of overweight, such as body composition and other cardiometabolic risk markers, needs to be investigated to fully assess the role of maternal vitamin D status for childhood adiposity and health. 

“As a proxy for adiposity, BMI might have low sensitivity in a child population and should be accompanied by other measures for robustness. The time point of maternal blood sampling also differs between studies, which may be of importance as there could be different windows of sensitivity of maternal vitamin D status on the foetus. 

“Also, the time point of investigation of the child’s anthropometry is likely of great importance. Adiposity rebound commonly occurs around 4–6 years of age when there can be a large difference in growth and body composition between children. As a result, some children might be incorrectly classified as having overweight.”

Journal: Frontiers in Nutrition

https://www.frontiersin.org/articles/10.3389/fnut.2023.1201171/full​

“Maternal vitamin D status and risk of childhood overweight at 5 years of age in two Nordic cohort studies.”

Authors: Anna Amberntsson, Linnea Bärebring, Anna Winkvist, Lauren Lissner, Helle Margrete Meltzer, Anne Lise Brantsæter, Eleni Papadopoulou, and Hanna Augustin.