Multivitamins, supplements overused during pregnancy, leading to potential harms - study

Pregnant women trying to stay healthy for their babies are relying too heavily on multivitamins instead of nutritious food and a balanced diet in their second trimesters, according to new research.  

The pilot study, led by University of the Sunshine Coast (UniSC) health researcher Dr Linda Gallo and Brisbane-based Mater Research associate professor Shelley Wilkinson, warns this over-reliance on supplements could lead to potential harms during pregnancy.  

The study, which was published in the journal Maternal and Child Nutrition late last year, involved surveys, health assessments and blood and plasma testing of 127 pregnant women attending Brisbane's Mater Mothers' Hospital in 2019. 

Almost 90 percent of the pregnant participants reported using supplements, with the majority opting for multivitamins to meet the dietary intake guidelines for folate, iodine and iron.  

Dr Gallo, a nutrition expert, said the findings have raised concerns about women intaking excessive amounts of nutrients during pregnancy.  

"Many women are taking these supplements as a pregnancy 'safeguard' without considering potential harms," Dr Gallo said. "In this study, more than 80 percent of participants were still taking a multivitamin in the second trimester, which is not consistent with guidelines."  

There are just two essential nutrients needed to be taken as a supplement or tablet during pregnancy, associate professor Wilkinson said - unless the mother is deficient in other vitamins or minerals.  

"Unless a deficiency in other vitamins and minerals is shown, the recommendation is to take an extra 400 micrograms per day of folic acid from the month before pregnancy to three months after you become pregnant - as well as a supplement containing 150 micrograms of iodine," she explained.  

"It's really important to be careful that you aren't overdosing on multivitamins - more is not always better - and mega-doses of vitamins and minerals can be harmful to your baby."  

Dr Gallo noted that overusing multivitamins and consuming high doses of folic acid, iron and iodine have previously been associated with negative outcomes for both mother and baby.

"These include gestational diabetes, preeclampsia, preterm birth, low birth weight, increased body fat and poorer neurodevelopmental outcomes," she said.

The experts have advised that in high-income countries such as Australia - where food is plentiful and fortification is mandated - multivitamins should be used with greater caution during pregnancy.

"A varied whole food diet offers superior benefits to supplements, although multivitamins may be appropriate for pregnant people who are unable to meet nutrient requirements through food alone," Dr Gallo said, while Wilkinson noted a "food first approach" is typically the healthiest.

"Food is where good nutrition starts... Making good food choices will usually minimise any need for supplements and will help you have a healthy gut microbiome."

The research is part of the long-term Queensland Family Cohort study in collaboration with The University of Queensland, which has been analysing the health of local families for five years.

Brisbane woman Claire Broesder, 30, is 37 weeks' pregnant and due to give birth next month. She has avoided taking multivitamins, but took the recommended folate supplements in her first trimester and was also prescribed an iron infusion by her doctor.

"During my pregnancy, especially in the second and third trimesters, I have been careful to eat a balanced, varied diet and it seems to be working - my baby is in one of the highest percentiles for growth," she reported as part of the research.

Based on the findings, the researchers suggest increased dietician involvement during pregnancy is needed.

Stock image of woman's pregnant belly
"A varied whole food diet offers superior benefits to supplements, although multivitamins may be appropriate for pregnant people who are unable to meet nutrient requirements through food alone." Photo credit: Getty Images

According to the New Zealand College of Midwives, eating healthy foods and a balanced diet is important during pregnancy. The organisation states that pregnant women should be consuming plenty of fresh fruit and vegetables, bread and cereals, milk and milk products, meat, seafood, legumes, eggs, nuts and seeds, with an emphasis on including all the main food groups. 

It also stresses the importance of limiting processed foods and drinks that are high in sugar, salt or fat.

The College of Midwives also recommends taking a daily folic acid tablet before pregnancy (if it is planned) and for the first three months, as well as supplementing iodine with a tablet during pregnancy and breastfeeding. It also suggests supplementing vitamin D in some specific cases. 

Women who adhere to a vegan or vegetarian diet may need additional nutrients such as iron and vitamin B12, but this should always be discussed with your midwife or a dietician.