Experts are urging women not to stop taking important nutrients such as iodine and folate during conception and/or pregnancy after media reports on a study which links multivitamin supplements to an increase in risk of miscarriage.
“As concluded by the [study] authors, it is critical that the data are not interpreted by health professionals and women contemplating pregnancy or already pregnant as evidence against…current clinical guidelines,” says Professor Lucilla Poston, head of the Division of Women’s Health at King’s College, London, UK.
In an accompanying editorial on the Danish data, both published in the International Journal of Epidemiology this month, Professor Poston also notes that the study data provides NO “strong enough reason to conclude that folate-only supplements should be preferred over multivitamins”.
The study, which used data of more than 35,000 mothers-to-be in the Danish National Birth Cohort, found women who had taken the supplements regularly in the six weeks before conceiving were around a third more likely to lose their baby early on.
“We found a modest but consistent increased risk of early foetal death in multivitamin users, especially in women with a regular preconceptional intake,” the authors, from the universities of Southern Denmark, Aarhus and Pittsburgh in the US wrote.
However, they also note that although their finding “causes concern” they were unable to explain why multivitamins raised the risk.
At recruitment the women had reported the number of weeks of supplement use during a 12-week periconceptional period. A telephone interview provided information about maternal characteristics and data on fetal death came from registers.
The data shows taking folate as a supplement on its own or in a multivitamin supplement while pregnant had a slight beneficial effect. But the study isolated a particular risk of miscarriage among those who took the multivitamin supplement several weeks before conception, in around a third of the women.
Compared with taking no pills at all, regular multivitamin use for three or four weeks beforehand saw the chances of losing the baby rise by 23 per cent. For the period of five to six weeks, it was 32 per cent.
Although the authors couldn’t find a reason for the trend, they were able to rule out links with obesity, smoking, poverty, previous miscarriage or difficulty in conceiving.
The jury is still out
In her editorial Professor Poston, says the study authors have acknowledged two potential causes of supplement-related miscarriage both suggested previously: first, that periconceptional multivitamin/ folate supplements may increase the risk of twin pregnancies which, in turn, heightens the risk of early foetal loss; and, second, that normally unviable pregnancies may be prolonged, leading to excess risk of death after 8 weeks of gestation. As no information was available on twin pregnancies before 28 weeks of gestation or on early abortions, these potential causes could not be addressed in the present analysis.
She also hypothesises that perhaps women taking prenatal supplements paid less attention to their diet, however, without blood analysis this is difficult to prove.
Finally, Professor Poston states: “None of the components of multivitamin supplements are likely to be directly harmful; the daily doses are within accepted recommendations, and because no other explanation springs to mind, one is led back to the possibility of residual confounding”.
The study authors themselves note that their findings are based on observational data and need replication, especially in lower socio-economic groups, but they highlight the lack of evidence for periconceptional multivitamin use on risk of miscarriage and stillbirth.
”It is, on the other hand, important to stress that this study does not provide evidence against use of folate supplements to reduce risk of neural tube defects and it is insufficient to change recommendations regarding multivitamins containing folate. Randomised trials and large observational studies, preferably preconceptional cohorts from different settings, are needed to guide public health recommendations,” they conclude.
Maternal health experts recommend women in Australia continue to take preconception and pregnancy multivitamins formulated in line with Australian guidelines and the TGA.
World-renowned Australian endocrinologist Professor Creswell Eastman, who has a primary interest in iodine deficiency disorders, believes that “until measures are taken to ensure that iodine needs can be met by usual dietary sources, pregnant and breastfeeding women should insist that the prenatal vitamins they are prescribed contain iodine.”
However, despite this strong recommendation there are still 40 per cent of pregnant women NOT taking iodine supplementation during pregnancy. It is also estimated that 50 per cent of pregnant women also do not take a folic acid supplement prior to becoming pregnant.
Research confirms that many Australians do not receive adequate nutrients from their diet alone. The 2012 Australian Food and Nutrition Report highlights that more than nine in 10 people aged 16 and over do not consume sufficient serves of vegetables, and about 50 per cent do not consume sufficient serves of fruit. Many Australian women are therefore not meeting the recommended daily intake (RDI) of key nutrients for a healthy pregnancy.
According to Blackmores Institute Director of Education, Pam Stone; “It is important to note that the needs of women in Australia can differ to those living in other parts of the world. For example, the World Health Organization guidelines for nutrient supplementation during pregnancy differ to the Australian guidelines for iron, iodine and folate.
“A variety of nutrients are needed for healthy conception and for the very early stages of foetal development. The overall nutritional status of the mother at the time of conception and during the first trimester is critical to the short and long term health outcomes of her baby,” says Ms Stone.
“Diet alone may not provide sufficient nutrition to meet these nutritional demands, in particular iodine and folic acid," she adds.
Inadequate nutritional status in Australia has led to the NHMRC recommending that all women considering pregnancy, or who are pregnant or breastfeeding take an iodine supplement of 150 micrograms/day as well as 500 micrograms of folate at least one month prior to conception and in the first trimester to reduce the risk of having a baby with neural tube defects.
Source: International Journal of Epidemiology 2013