Monday April 6 2009
Vitamin E supplements are not recommended during pregnancy
New research has shown that “Vitamin E ‘can increase the risk of heart defects in babies,’” says the Daily Mail. The newspaper warns that consuming as little as three-quarters of the recommended daily amount of vitamin E while pregnant can lead to a nine-fold increase the risk of a heart problem at birth.
The research compared the diets of women with healthy babies and babies born with congenital heart defects. Mothers of babies with heart defects were found to have consumed higher amounts of vitamin E. However, the research is limited by mothers’ diets being assessed when their children were already 16 months old, which may not reflect diet around the time of conception and birth.
Despite limitations to this research, the possible association between high vitamin E intake and congenital heart defects is an important one requiring further research. UK guidance currently gives no recommendations on taking vitamin E during pregnancy. At present, it may be sensible for pregnant women to not be overly concerned by vitamin E naturally occurring in foods and continue to eat a healthy, balanced diet but to consider avoiding vitamin E supplements.
Where did the story come from?
HPM Smedts and colleagues from University Medical Centre, Rotterdam, and other institutions in the Netherlands carried out this research. The study was funded by a grant from the Corporate Development International and the Netherlands Heart Foundation and published in the peer-reviewed medical journal, the British Journal of Obstetrics and Gynaecology.
What kind of scientific study was this?
This was a case-control study examining possible associations between congenital heart defects (CHDs) and maternal intake of vitamin E and retinol. Retinol is the active form of vitamin A that has previously been associated with CHDs.
The case-control study involved Dutch mothers, 276 of whom had given birth to a child with a congenital heart defect (the case group) and 324 of whom had given birth to a healthy child (the control group).
The study involved children from the Dutch HAVEN study (a Dutch acronym for Heart Defects, Vascular Status, Genetic Factors and Nutrition) who were identified as having a CHD in the first year of life and were under cardiology care.
These children had various congenital defects, including Tetralogy of Fallot, atrioventricular or ventricular septal defects, aortic or pulmonary valve stenosis, coarctation of the aorta, transposition of the great vessels, and hypoplastic left heart syndrome. The cases involved 56 children with non-isolated heart defects, who also had other congenital abnormality, including 26 cases of Down’s syndrome. Healthy control children were selected through routine attendance at health centres.
Parents of both groups of children attended an assessment at 16 months after birth. They completed food frequency questionnaires covering the intake of the previous four weeks. The questionnaires consisted of 195 food items, structured according to a meal pattern and including questions about preparation methods, portion sizes and extras. They used an electronic version of the Dutch food composition table to calculate average daily intake of retinol and vitamin E.
Mothers were also asked questions on their own health and lifestyle in the weeks prior to and following conception, covering information on age, BMI, diabetes, family history of CHD, alcohol, smoking and other factors. They were also asked specific questions about vitamin supplements, including information on the contents (folic acid only or multivitamin supplement containing vitamin E and/or retinol), dosage and frequency of intake.
Data between groups was compared and risk estimates for the association between CHD and dietary intake of vitamin E and retinol were estimated.
What were the results of the study?
Case mothers were found to be slightly older than control mothers (average age 33.1 versus 32.7). There was no difference between mothers in their medical history or family history of CHDs. There was no difference between case and control mothers in their use of tobacco, alcohol or use of vitamin supplements, either around the time of conception or at the time of assessment (16 months following birth).
Total energy and retinol intakes were similar in both groups of mothers, but case mothers showed significantly higher dietary vitamin E intake than controls, with intakes of 13.3 mg/day versus 12.6mg/day.
Further analysis showed that in women who used a supplement containing vitamin E around the time of conception, there was a trend towards a higher CHD risk with rising dietary vitamin E intake. Dietary vitamin E levels of above 14.9mg/day increased the risk of CHD by six times (after adjustment for mother’s age and use of vitamin supplements).
What interpretations did the researchers draw from these results?
The researchers conclude that high intake of vitamin E through diet or supplements is associated with an increased risk of congenital heart defects.
What does the NHS Knowledge Service make of this study?
This research demonstrated that 276 mothers of children with congenital heart defects had an average daily intake of 13.3mg compared to 324 mothers of healthy children who had an average daily intake of 12.6mg. At the highest levels of intake (above 14.9mg/day) this was associated with a six-fold increase in CHDs.
However, there are some important limitations to this research:
- Although the researchers made an effort to exclude mothers who reported a change in their dietary pattern over the months from pregnancy to time of current assessment, the principle limitation to the study is that the mother’s diet was assessed only when the child was already 15 to 16 months old, rather than at time of conception. Therefore, the possibility remains that the woman’s current diet may differ from her diet around the time of conception.
- There is also the possibility of recall bias in this study: that a woman whose child has a CHD may try to find reasons for the condition and recall her diet differently (although the women were not specifically informed of the nature of the study).
- However, as the researchers say, both of the above limitations are hard to avoid as most congenital anomalies are diagnosed in the first year of life, and assessing the women sooner after birth means there could have been the influence of physical and dietary changes due to breastfeeding and recovery after pregnancy.
- Although computer programs were used to quantify vitamin E intake from the foods reported, there is likely to be some degree of inaccuracy in the calculated amounts.
- The cases do not involve one particular congenital heart defect, but a range of different heart defects and congenital syndromes (such as Down’s), all of which may have slightly different risk factors. It has not been able to make an in-depth assessment and take these varying risk factors into account.
Despite the limitations, further research is needed into the important question of whether high amounts of vitamin E in the diet during pregnancy increase the risk of congenital heart defects in newborns.
Vitamin A (retinol) has already been associated with causing harm to the development of the fetus and for this reason, NICE guidance advises against consumption above 700 micrograms per day during pregnancy. There are currently no such recommendations on safe vitamin E levels during pregnancy.
Vitamin E is important to human health and is found naturally in numerous foods including nuts, avocado and olive oil. At the current time, it may be sensible to advise pregnant women that they should not be overly concerned by vitamin E within foods and continue to eat a healthy, balanced diet, but to consider avoiding taking supplemental vitamin E tablets.