Personal Health Navigator

Why herbal supplements should be avoided during pregnancy

pregnant woman holding bottle of vitamins
Written by Paul Taylor

Question: My daughter has always taken a lot of herbal supplements, which she buys at a health food store.  Now, she is pregnant and she’s consuming even more of this stuff. Is this a good or bad thing to do?

Answer: There is a lot of uncertainly around herbal products – especially when used during pregnancy.

Supplements don’t go through the same testing and approval process as prescription and over-the-counter medications. The exact combination of ingredients might vary from manufacturer to manufacturer – and some may contain impurities. Suspected cases of negative reactions are occasionally reported in the medical literature. In general, though, they are not systematically studied.

“We don’t know what the impact would be in pregnancy for many herbal supplements,” says Dr. Batya Grundland, the maternity-care lead for the family health team at Women’s College Hospital in Toronto.

“That doesn’t mean they’re all bad. We just lack the information to guide women in very specific ways.”

For that reason, Dr. Grundland and other maternity experts urge women to be cautious. “It’s a bit of a black box,” she says.

What can be said with some certainty is that pregnant women do need a variety of vitamins and minerals for the normal growth of the fetus.

For instance, folic acid or folate – a B vitamin – is necessary for the proper formation of the spine, brain and skull, particularly during the first month of pregnancy.

This critical development begins at a time when a woman may not realize she is pregnant, says Daphna Steinberg, a clinical dietitian at Sunnybrook Health Sciences Centre.

So, public health agencies recommend that women who might become pregnant take a daily supplement containing 400 micrograms of folic acid to ensure they have adequate levels of the vitamin to prevent birth defects such as spina bifida.

As the pregnancy progresses, women require sufficient levels of other nutrients. Among other things, iron is needed to produce additional blood for mother and child. And calcium plus Vitamin D are critical for bone formation.

It’s possible to get most of the essential nutrients by eating a healthy and varied diet, says Ms. Steinberg.

Of course, morning sickness, which plagues many pregnant women, can stymie their best efforts to eat well.

A standard prenatal supplement, which can be purchased at a pharmacy, should safely provide the basics. But on the downside, a supplement – especially one containing iron – may contribute to feelings of nausea and constipation.

This gastrointestinal distress might be eased in various ways. For some women, it may be appropriate to switch to a children’s vitamin, which contains a lower dose of iron. Another option is to split a prenatal vitamin in two and take the separate halves at different times of day in order to improve tolerability.

Women shouldn’t consume extra supplements, unless they are told to do so by their doctors. More is not necessarily better and may actually be harmful. High levels of folic acid, for example, can hide signs of vitamin B12 deficiency.

Yet the potential problems of excessive dosing is a hard message to get across – especially to those who are regular consumers of herbal products, says Ms. Steinberg.

“I had a patient who came in with a bag literally full of herbals that she was taking. We went through them ingredient by ingredient, checking them with a database of known and potential risks, ’’ she recalls.

Blue cohosh has been linked to heart problems and other abnormalities in newborns.  Agnus castus, a plant with estrogen-like properties, may increase the risk of miscarriages. For many products, however, there is no reliable safety information.

“I see a lot of women who want to do the absolutely best thing for their babies,” says Ms. Steinberg. “Rather than buying a standard prenatal supplement, they will spend extra money on ‘organic’ and ‘natural’ herbals and they could be unknowingly choosing things that are unsafe in pregnancy.”

It’s also important to keep in mind that some herbal teas might cause problems, too. Health Canada recommends that pregnant women should avoid certain teas, including those containing chamomile, aloe, coltsfoot, juniper berry, pennyroyal, buckthorn bark, comfrey, labrador tea, sassafras, duck root, lobelia and senna leaves. Other herbal teas should be consumed in moderation – no more than two or three cups a day.

“In my opinion, herbal supplements are not worth the risk,” says Ms. Steinberg.

About the author

Paul Taylor

Paul Taylor, Sunnybrook’s Patient Navigation Advisor, provides advice and answers questions from patients and their families, relying heavily on medical and health experts. Email your questions to AskPaul@sunnybrook.ca
and follow me on Twitter @epaultaylor