Could Low Vitamin D Be a Piece of the Childhood Obesity Puzzle?
Childhood obesity is attracting much attention because of its long-term effects of early obesity on health over the lifespan. It is attracting attention from international groups (World Health Organization), national-based programs (Let’s Move from First Lady Michelle Obama), and considerable media interest, for example from celebrity chef Jamie Oliver. One nutrient that is the focus of considerable research interest is vitamin D. Authors Crozier et al. in the online first articles of the American Journal of Clinical Nutrition reported on the link between maternal vitamin D status during pregnancy, and fat mass in their children up to 6 years of age in women living in the city of Southampton, one of the more sunny cities in the UK.
Women were recruited as part of a prospective cohort study of over 12,000 women aged 20-34 living in the city. For this particular study, women who became pregnant were followed up during pregnancy at weeks 11, 19 and 34; their infants were visited at 6, 12 and 24 months, 4 and 6 years. DEXA was used to measure body composition in a subset of children. Maternal serum hydroxyvitamin-D concentrations were measured by radioimmunoassay, as well as standard measurements such as body mass index, food frequency questionnaire, and vitamin D intake from supplements. Strong seasonality was seen in vitamin D measurements therefore they were transformed statistically to account for this.
Almost half the women in the study were overweight or obese, and 15% smoked during pregnancy. Around 35% of the women had insufficient levels of vitamin D (less than 50 nmol/L). When looking at fat mass at birth, lower maternal vitamin D levels were associated with lower fat mass in infants. At four and 6 years, the unadjusted fat mass was increased for children of mothers with lower vitamin D levels, and this remained significant at 6 years after adjustment for confounders, which included maternal body mass index.
It is not known why vitamin D contributes to obesity, as has been found in population-based surveys, as reviewed by Song and Sergeev. As vitamin D is fat soluble, people with a higher percentage of body fat have lower vitamin D concentrations due to a dilution effect, and environment is likely to link overweight mothers with overweight children, although in this study body mass index was adjusted for in the model. Vitamin D is needed to maintain muscles, and muscle weakness is a symptom of vitamin D deficiency; low muscle tone may reduce metabolic rate (more details in this review by Ceglia). The vitamin D receptor is involved in energy regulation, as described by a group lead by Wong. Clearly more research is needed, and should be directed towards whether vitamin D supplements or adequate vitamin D nutrition can provide a piece to help solve the childhood obesity puzzle. -jb-
Sarah R Crozier, Nicholas C Harvey, Hazel M Inskip, Keith M Godfrey, Cyrus Cooper, Siân M Robinson, and the SWS Study Group. Maternal vitamin D status in pregnancy is associated with adiposity in the offspring: findings from the Southampton Women's Survey. Am J Clin Nutr 2012 ajcn.037473; First published online May 23, 2012. doi:10.3945/ajcn.112.037473