RESEARCH - Mother's vitamin D during pregnancy affects child's bone mass

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Mother's vitamin D during pregnancy affects child's bone mass

Rheumawire

Jan 9, 2006

Janis

Southampton, UK - The first study to examine mothers' vitamin-D levels

during pregnancy in relation to the bone mass of their children found that

nearly 50% of the mothers had low or very low levels of circulating

25(OH)-vitamin D during the last trimester and that these deficiencies were

associated with reduced bone-mineral accrual in their offspring during

childhood. The study was reported by Dr MK Javaid (Southampton General

Hospital, Southampton, UK) and colleagues in the January 7, 2006 issue of

the Lancet [1].

Senior author Dr Cyrus (Southampton General Hospital) said in a

prepared statement, " These findings provide evidence that maternal vitamin-D

status during pregnancy influences the bone growth of the offspring and

their risk of osteoporosis in later life. The results add to a large body of

evidence that intrauterine and early postnatal development contributes to

bone accrual and thereby osteoporosis risk. They also point to preventive

strategies that now require evaluation in randomized controlled trials. "

Study followed 198 mothers and children for nine years

The study followed 198 mother-child pairs from early pregnancy through the

child's ninth year. The mothers were participants in a long-term study of

maternal nutrition and fetal growth. At about 34 weeks' gestation, serum

samples were taken from the mothers for analysis of serum 25(OH)-vitamin D

by radioimmunoassay, which measured both vitamin D2 and D3. The mothers were

classified as vitamin-D replete (>20 g/L), insufficient (11-20 g/L), or

deficient (<11 g/L).

Exposure to UVB light was estimated from the hours of sunshine per month of

pregnancy recorded at a local meteorological station.

After delivery, samples of umbilical-vein blood were taken and later

analyzed for concentration of ionized calcium.

About nine years later, the women and children attended a follow-up

examination that included information on socioeconomic status and diet and

exercise of both mother and child (including milk intake). The children also

had whole-body and lumbar-spine bone-mineral content (BMC), bone area, and

area bone-mineral density (BMD) measurements by dual-energy x-ray

absorptiometry (DXA).

These analyses showed that:

Reduced maternal vitamin-D levels during late pregnancy were

associated with lower whole-body and lumbar-spine BMC in their children at

age nine years.

Reduced umbilical-venous calcium also predicted reduced bone mass in

children.

Low vitamin-D levels were very common in the mothers during pregnancy

(31% insufficient, 18% deficient).

Bone mass was higher in children whose mothers had taken vitamin-D

supplements.

The two best predictors of maternal concentrations of 25(OH)-vitamin D in

late pregnancy were UVB exposure and the use of vitamin-D supplements. The

best predictor of childhood whole-body BMC was the calcium concentration of

umbilical-cord blood.

" Our study provides direct evidence that the intrauterine environment, as

indicated by maternal vitamin-D status during pregnancy, is significantly

correlated with bone-mineral density at age nine years, " the authors write.

They suggest that this effect is mediated by epigenetic mechanisms such as

the methylation status of imprinted genes that regulate fetal and placental

growth, as well as specific transport systems. About 80% of the calcium

transfer from mother to fetus in utero occurs during the last trimester of

pregnancy, and that transfer capacity depends in part on maternal calcium

intake and vitamin-D status.

" We postulate that maternal vitamin-D insufficiency during pregnancy leads

to an impairment of placental calcium transport, perhaps mediated by

parathyroid-hormone-related peptide (PTHrP), and thereby reduces the

trajectory of intrauterine and subsequent childhood bone-mineral accrual, "

the authors write.

Problem only when vitamin-D levels are deficient

Commenting on the new findings in a BBC News article, Prof

(Royal College of Obstetricians and Gynaecologists, London, UK) said the

study demonstrated the importance of having adequate levels of vitamin D in

pregnancy, both for the mother and her baby. But he said it demonstrated

that women who had adequate vitamin-D levels were fine, and it was " only

when levels were deficient that there was a problem. "

" More vitamin D is not necessarily good, " he said. " Therefore, no woman

should take extra vitamin D in pregnancy unless recommended by their

doctor. "

Source

1. Javaid MK, Crozier SR, Harvey NC, et al. Maternal vitamin

D status during pregnancy and childhood bone mass at age 9 years: a

longitudinal study. Lancet 2006; 67:36-43.

Not an MD

I'll tell you where to go!

Mayo Clinic in Rochester

http://www.mayoclinic.org/rochester

s Hopkins Medicine

http://www.hopkinsmedicine.org