Vitamin D has been linked to a number of beneficial health effects; from strengthening bones, to protecting against infections and rickets, right through to potentially influencing the risk of developing multiple sclerosis and certain cancers.
Yet the essential vitamin, sometimes referred to as the sunshine vitamin because of our ability to synthesise it from sunlight, could potentially have damaging effects if supplements are taken in excess during pregnancy, according to new research published in the academic journal Allergy.
Led by Dr Kristin Weiße from the Helmholtz Centre for Environmental Research, Germany, the team of researchers warn against pregnant taking vitamin D supplements, as it appears to be linked to an increased risk of children developing food allergies after birth.
“Based on our information, an excess of vitamin D can increase the risk of children developing a food allergy in the first two years of their life,” said Weiße.
Weiße and her team used samples from a previous research study known as ‘Lifestyle and environmental factors and their impact on the newborn allergy risk’ (LiNA) that ran from 2006 to 2008.
The new analysis of data from this study included 622 mothers and their 629 children, all of whom had been tested for their vitamin D levels during pregnancy and also in the cord blood of the children born.
In addition to this, questionnaires were used to assess the occurrence of food allergies during the first two years of the children’s lives, explained Weiße and her colleagues.
The result was clear, they said. In cases where expectant mothers were found to have a low vitamin D level in the blood, the occurrence of food allergies among their two-year old children was rarer than in cases where expectant mothers had a high vitamin D blood level.
In reverse, this means that a high vitamin D level in pregnant women is associated with a higher risk of their children to develop a food allergy during infancy, warned Weiße.
The research group also found that children whose mothers had a high intake of vitamin D had a high level of the specific immunoglobulin E to food allergens such as egg white, milk protein, wheat flour, peanuts or soya beans.
After taking a closer look at the immune response of the affected children, and in particular analysing samples of cord blood to test for the activity of immune regulator cells known as regulatory T-cells (Treg), the German scientists suggested that there is evidence for a biological mechanism to link vitamin D with the increase in allergy.
Noting previous work in the area, the team explained that such Treg cells are capable of preventing the immune system from overreacting to allergens, with the result that they protect against allergies. As a result, too few Tregs can lead to an increase in allergy.
Weiße and her team have now shown that the higher the level of vitamin D found in the blood of mothers and children, the fewer Tregs could be detected.
Such a correlation could mean that vitamin D suppresses the development of these regulatory immune cells and therefore can increase the risk of allergy, they said.
According to Weiße, even though the occurrence of food allergies is undoubtedly affected by many other factors than just the vitamin D level, it is still important to take this aspect into consideration.
Volume 68, Issue 2, pages 220–228, February 2013, doi: 10.1111/all.12081
"Maternal and newborn vitamin D status and its impact on food allergy development in the German LINA cohort study"
Authors: K. Weisse, S. Winkler, F. Hirche, G. Herberth, D. Hinz, et al