A study with guinea pigs has revealed that sufficient vitamin D for a newborn may not be sufficient to reverse vitamin D deficiency in the womb, researchers from McGill University in Quebec report in the Journal of Nutrition.
“This study demonstrates the importance of vitamin D in bone health as well as the implications that a mother’s nutrient deficiency has a profound effect on her offspring during gestation and infancy” wrote the researchers, led by Dr Hope Weiler.
“This study is highly suggestive that efforts to optimize maternal vitamin D status in pregnancy are needed along with maintenance in infancy rather than relying on postnatal supplementation to restore vitamin D status and bone mass.”
A recent study based in Northern Ireland indicated that many mothers may not be getting enough vitamin D, even those taking supplements at the recommended doses (British Journal of Nutrition, Vol. 102, pp. 876-881). Almost all of the women in the study had blood levels of the vitamin below 80 nmol/l: A level which is widely considered to be the cut-off for vitamin D sufficiency, showing that current recommendations may be insufficient.
In the US and Canada there are currently no specific recommendations for pregnant women, and adequate intakes are inline with the general population (5 micrograms per day). On the other side of the Atlantic in the UK, pregnant women are recommended by the Food Standards Agency (FSA) to take supplements with a daily dose of 10 micrograms vitamin D.
The importance of vitamin D during pregnancy for bone development is widely recognised. According to the new study, the developing fetus accumulates about 30 grams of calcium in the womb.
“Although vitamin D deficiency can be reversed in human infants through supplementation, it is unclear if deficiency in utero and neonatally continues to manifest as low bone mass and altered bone metabolism despite correction of vitamin D status,” explained Dr Weiler and her co-workers.
In order to assess the effects of vitamin D in utero and neonatal, the McGill scientists studied pregnant guinea pigs fed either a diet containing adequate vitamin D levels or a diet with deficient levels of the sunshine vitamin.
Pups from both groups were then randomized to receive a daily oral vitamin D supplement providing 0.25 micrograms per day or placebo supplement for 28 days. This dose is equivalent a 4kg infant receiving 10 micrograms of the vitamin per day, said the researchers.
The results showed that pups of mothers in the deficient group had lower bone mineral content, 6.2 percent lower blood levels of osteocalcin (a protein that is essential for the body to utilise calcium in bone tissue), lower body weight, and the animals were shorter in length, regardless of the pups own supplementation.
“Although postnatal vitamin D supplementation was in part successful in restoring vitamin D status, supplementation did not have a significant effect on bone mass or markers of bone modelling,” wrote the researchers.
“Longer-term studies are required to establish the implications to bone later in life,” they concluded.
At the start of August, scientists in Europe and the US called for an increase in daily recommendations for Vitamin D, which they say is crucial to protect against conditions such as childhood rickets, adult osteomalacia, cancer, autoimmune type-1 diabetes, hypertension, cardiovascular disease, obesity and muscle weakness.
Writing in the July 28 issue of Experimental Biology and Medicine, the authors propose worldwide policy changes to increase recommended intake levels of the sunshine vitamin. This, they said, would reduce the frequency of certain diseases, increase longevity and reduce medical costs.
"It is high time that worldwide vitamin D nutritional policy, now at a crossroads, reflects current scientific knowledge about the vitamin's many benefits and develops a sound vision for the future," said Anthony Norman, a professor emeritus of biochemistry and biomedical sciences at the University of California, Riverside.
Source: Journal of Nutrition
Volume 140, Pages 1574-1581
“Postnatal vitamin D supplementation following maternal dietary vitamin D deficiency does not affect bone mass in weanling guinea pigs”
Authors: S.L. Finch, F. Rauch, H.A. Weiler