Women in the lowest tertile of vitamin D blood concentrations (< 37.7 nanomoles/litre (nmol/l) (15.2 nanograms/ millilitre (ng/ml)) gave birth to children who had larger waist circumferences and higher body mass index (BMI) at age 4 years.
The observed associations also persisted at age 6 years, noted the research team led by the Keck School of Medicine, University of Southern California (USC).
“Our findings support that very low vitamin D concentrations in the first half of pregnancy may increase offspring adiposity indices at preschool and school age,” commented senior author Professor Vaia Lida Chatzi.
At age 4 years, the difference in waist circumference between children of mothers in the lowest tertile versus other tertiles of maternal vitamin D concentration was 0.87 centimetres (0.34 inches).
This increased adiposity could have health implications in later life, explained Chatzi.
"These increases may not seem like much, but we're not talking about older adults. Even a half-inch increase in waist circumference is a big deal, especially if you project this fat surplus across their life span."
The prospective study included 532 mother-child pairs in Greece. Maternal serum vitamin D levels were examined at the first prenatal visit during pregnancy (around 14 weeks gestation). The child’s height, weight and waist circumference were measured at age 4 and 6 years. Blood pressure and blood fats were also analysed in the children, although no association with maternal vitamin D levels was observed in these outcomes.
Public health implications
The prevalence of vitamin D deficiency in the study came as a surprise to the researchers, give that Greece is a country that enjoys reasonable levels of sunshine, even during the winter. Furthermore, none of the women in the study took vitamin D supplements.
"We're not sure why there is vitamin D deficiency even in places with abundant sunshine, but maybe people are spending too much time indoors," Chatzi said. "Or maybe they're using excessive amounts of sunscreen, which inhibits vitamin D production."
The deficiency threshold is widely regarded to be a blood concentration below 50 nmol/l (20ng/ml), with insufficiency classified as 50-75 nmol/l (20-30 ng/ml).
Apart from the possible higher obesity risk in offspring, vitamin D deficiency in pregnancy has been linked in previous research to adverse health outcomes such as preeclampsia, low birthweight, neonatal hypocalcaemia, poor postnatal growth, bone fragility, and increased incidence of autoimmune diseases.
The researchers speculated on a possible mechanism underlying the link between low vitamin D levels and obesity.
"It's possible that children of mothers with low vitamin D have higher body mass index and body fat because vitamin D appears to disrupt the formation of fat cells," said Chatzi. "Optimal vitamin D levels in pregnancy could protect against childhood obesity, but more research is needed to confirm our findings. Vitamin D supplements in early pregnancy is an easy fix to protect future generations."
“Further studies and clinical trials are needed to explore the role of vitamin D supplementation during pregnancy in childhood obesity,” advocated the researchers.
Source: Pediatric Obesity
Published online, doi: 10.1111/ijpo.12267
“Low maternal vitamin D status in pregnancy increases the risk of childhood obesity”
Authors: V. Daraki, L. Chatzi et al