Pregnant woman holding her belly, representing healthy pregnancy and nutrition
Nutrition

Pregnancy supplements: what to take and what to avoid

by admin

The truth is most people who already eat a varied diet don’t need a shelf full of supplements. Some are really important; some are only important to some people and a handful of popular products can actually cause harm. The difficult part is distinguishing between them, which is why you don’t want to make this a DIY decision at the pharmacy or on the internet. Several things that sound healthy (vitamins sold freely over the counter) are unsafe in high amounts during pregnancy. It’s not a harmless risk to start a product because the label looks reassuring.

Here’s what the evidence supports and what to put back on the shelf.

An assortment of vitamin and supplement pills and capsules

The one thing to fix before you get pregnant

Folic acid has the longest and most convincing track record of any pregnancy supplement. Public health agencies, such as the US Centers for Disease Control and Prevention, the Institute of Medicine, and the US Preventive Services Task Force, recommend that all women capable of becoming pregnant consume 400 micrograms of folic acid daily. It’s the timing that makes it work. Obstetricians recommend starting at least a month before conception and continuing through the first 12 weeks of pregnancy, because the neural tube forms and closes during the third and fourth weeks of pregnancy, often before a woman knows she is pregnant.

The payoff is huge. Numerous studies have demonstrated that taking folic acid before and during pregnancy lowers the risk of neural tube defects, such as spina bifida and anencephaly. If you have had a previous pregnancy with a neural tube defect, your situation is different. So, the guidance is to take a much higher dose, 4,000 micrograms a day, from one month before conception through the first three months, and that dose should be prescribed and monitored by your provider.

For more on getting this right before you conceive, check out our companion article, “Folic acid, or vitamin B9: the right step to prepare for pregnancy.”

The vitamin people often miss

Food often falls short on vitamin D and sunlight is unreliable for much of the year. UK health bodies including NICE and NHS recommend that all pregnant women take a daily 10 microgram (400 unit) vitamin D supplement, and that those with darker skin or who cover their skin may need to do so all year round. NICE guidance goes further to recommend 10 micrograms throughout pregnancy ideally from before conception. Vitamin D is very safe at this dose and is important for your and your baby’s bone and muscle health. One warning applies here and is repeated below: do not supplement your vitamin D with cod liver oil.

Vitamin B12 if you eat few or no animal foods

Vitamin B12 is found only in animal foods. If you don’t eat these foods, you run the risk of a vitamin B12 deficiency which can cause anemia. In a baby it can cause serious harm. Adults build up B12 stores that can last for two to four years, but babies haven’t built up those stores, so without enough B12 an infant can develop brain damage. The deficiency can take a long time to show up, which makes it easy to miss. A 2021 review in the European Journal of Haematology noted that, as veganism and vegetarianism become more common, prophylactic vitamin B12 supplementation should be offered to high-risk groups in the periconceptional period.

So even if you eat a varied diet, talk to your doctor or midwife about B12 and take a supplement if you need to. A good dose for those who need it is 10 micrograms a day, says the British Dietetic Association, and it is better absorbed in small frequent doses than one large dose.

Iron: helpful if you need it, but not something to self-prescribe

Iron is a perfect example of why self-dosing is a bad idea. Where anemia is common in pregnancy, routine supplementation is the norm. The World Health Organization recommends daily oral iron and folic acid as part of antenatal care to reduce the risk of low birth weight, maternal anemia and iron deficiency. In lower-risk settings, the approach is based on testing. The advice is to assess iron status and where less than 20 per cent of pregnant women are anemic, intermittent rather than daily iron can be used for those who are not anemic. To summarize, some situations make you more at risk of iron deficiency and your doctor or midwife will check if this applies to you. If you are taking iron on your own, in supplements or in fortified foods, you don’t have to and it can cause side effects.

Two habits to help you absorb more iron from foods. Don’t drink tea before, during or after meals as it will interfere with the absorption of iron from plant foods. And pair those foods with vitamin C: combining iron with a source of vitamin C such as lemon, broccoli, spinach or tomatoes helps absorption.

Liver and vitamin A: when a healthy food turns dangerous

Liver is high in iron and B12. That’s why it’s so often recommended. The trouble is it’s also extremely high in preformed vitamin A, otherwise known as retinol. High doses of preformed vitamin A are known teratogens, meaning they can cause fetal malformations.

The numbers speak for themselves. Women of childbearing age must not exceed 3,000 micrograms a day of preformed vitamin A, according to European food safety authorities, who have based this limit on the risk of teratogenicity and liver toxicity, and this applies to pregnancy. Liver alone can get you over that limit. A single 3-ounce serving of beef liver can contain as much as 15,000 to 27,000 units of vitamin A, enough to put you over the recommended daily limit in one sitting. The clearest human evidence is a 1995 study published in the New England Journal of Medicine. It tracked 22,748 pregnant women, and those who took more than 10,000 units a day of supplemental preformed vitamin A had about five times the rate of certain cranial birth defects as other women, with the excess risk concentrated before the seventh week of pregnancy.

Pregnant women are therefore advised not to eat liver and products made from it, such as liver pâté or foie gras. The same caution applies to supplements. UK government advice states that pregnant women or those thinking of having a baby should not take supplements containing vitamin A, such as fish liver oil (like cod liver oil), unless their doctor tells them to.

If you’ve already had some liver or pate, don’t panic. The risk is from repeated high intake over time, not one meal. It is also useful to know that the vitamin A that comes from vegetables is different. The plant form, beta-carotene, only converts to retinol as the body needs it, and is not teratogenic from food, so colourful vegetables are not a concern.

The ‘cholesterol-lowering’ yogurts and spreads: steer clear for now

Some commercial products such as yogurts, dairy drinks and margarines claim to lower cholesterol by the presence of phytosterols. Phytosterols are compounds found naturally in plants that can help reduce blood cholesterol levels. They are not recommended during pregnancy and breastfeeding for two reasons. The intake of phytosterols lowers the plasma concentration of beta-carotene, which matters because beta-carotene is important for fetal growth. And the benefit is not as advertised. France’s food safety agency, ANSES, examined these products and found that there was no evidence of benefit for preventing cardiovascular disease and advised pregnant and breastfeeding women to avoid them.

Fortified foods and the bottom line

If you’re eating a varied diet, you usually don’t need to eat foods fortified with specific nutrients that are marketed to pregnant or breastfeeding women. Your plate does the bulk of the work.

Some supplements with good evidence behind them are folic acid before and in early pregnancy, vitamin D throughout, and vitamin B12 if you eat little or no animal food, plus iron and iodine when a clinician advises it. Everything else is worth a chat first. Your diet may not be meeting all your needs and the only way to know is to discuss with your doctor or midwife. In this case more isn’t better and some of the healthiest looking products on the shelf are ones to leave on the shelf.

Frequently asked questions

Do I still need supplements if I eat a healthy, varied diet?

Usually just two: folic acid before and in early pregnancy, and vitamin D throughout. Add vitamin B12 if you eat little or no animal food. Iron and iodine only come in if your doctor or midwife says so. Foods fortified for pregnant women are mostly unnecessary when your diet is already varied.

When should I start taking folic acid?

At least a month before you try to conceive and keep going through the first 12 weeks. The usual dose is 400 micrograms a day. The higher 4,000 microgram dose is only for women who have had a pregnancy affected by a neural tube defect, and only when a provider prescribes it.

Is it safe to eat liver during pregnancy?

It’s better to skip it. Liver and liver products like pâté and foie gras are very high in preformed vitamin A, which can harm the baby in large amounts. If you’ve already had some, one meal isn’t a reason to worry.

Which supplements should I avoid during pregnancy?

Any supplement containing vitamin A (retinol), including fish liver oil and cod liver oil, unless your doctor advises it. Also skip the ‘cholesterol-lowering’ phytosterol yogurts, drinks and spreads.

Can vegetarians and vegans get enough B12 while pregnant?

Not reliably from food, since B12 is only in animal products. A daily supplement of around 10 micrograms covers it for most people but check with your doctor or midwife first.

Resources

A note on this article: the information here is drawn from published scientific research and guidance from recognised health authorities, listed in the resources above. It is for general education only and is not medical advice. Every pregnancy is different, so always consult your own doctor or midwife before you start, stop, or change any supplement.

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