Prenatal Vitamins: What to Know and What to Avoid

Are prenatal vitamins necessary? Women are supposed to take prenatal vitamins to ensure the healthy growth of their babies during pregnancy. But, with so many options and doses for prenatal vitamins and supplements available on the market, choosing the best prenatal vitamin can be a confusing decision. Even more confusing, some of the benefits of prenatal vitamins depend on factors like your diet and weight.

So, should you take prenatal vitamins?

The answer is YES, but there are several things to keep in mind about what vitamins you need. This post will cover the science-backed do’s and don’ts of prenatal vitamins so that you can make the best decision for you.

DO know the purpose of prenatal vitamins before taking them

Before taking vitamins, whether a specific vitamin or a multivitamin, it is important to understand the purpose of vitamins in the first place. Vitamins are nutrients that the body cannot make but still needs to function. This means we need to get vitamins from outside sources, either from our food or from a dietary supplement.

If you already eat a nutritious and varied diet, you are likely getting enough vitamins. However, if you’re allergic or intolerant of certain foods, are vegan or vegetarian, or lactose-intolerant, then you might be running low on certain vitamins and a supplement could help.

During pregnancy, the body requires higher levels of vitamins to support fetal growth. It may be difficult for women trying to conceive or who are already pregnant to meet the increased vitamin requirements from diet alone, especially if they are struggling with morning sickness or dietary restrictions. For this reason, it is recommended that women who are pregnant or trying to conceive take a prenatal vitamin supplement to ensure they meet their vitamin requirements.

DON’T overdo it; you can have too much of a good thing when it comes to vitamins

You may have heard the antiquated adage that “vitamins can only help, not hurt” or “you can’t have too much of a vitamin.”

Neither of those statements is true.

In fact, having too much of certain vitamins can be toxic. Excess calcium, vitamin A, and vitamin D, and iron can be damaging and even fatal. And the research is still inconclusive about whether excess of other vitamins, like folic acid, is also harmful.

On the other hand, vitamin deficiency is linked to adverse outcomes. Folate deficiency, for example, is linked to neural tube defects in developing babies. And insufficient vitamin A is linked to blindness. Vitamin supplements, when you need them, can help prevent adverse outcomes.

So, how do you know how much of a vitamin you should be taking? This table shows the recommended and the upper limits for vitamin intake during pregnancy.

But, it would be difficult to track your daily vitamin intake of every single vitamin and balance getting the right amount. If you’re already eating a healthy and varied diet, the key prenatal vitamins to look for are folate, vitamin D, calcium, and iron.  You can ask your doctor to check for signs of vitamin deficiency, like anemia (low iron), so you can determine if there are specific doses to choose or if there are additional vitamins important for your health.

The good news is that it is rare to exceed vitamin tolerance from diet or one multivitamin (or prenatal vitamin). However, it may be more problematic if you are using more than one vitamin supplement or taking more than one supplement per day. If you notice any stomach trouble, skin changes, muscle weakness, or faster heartbeat, contact your doctor about lowering vitamin dosage or changing vitamins (full list of vitamin overdose signs here).

DO include folate but know the difference between folate and folic acid

One of the most important prenatal vitamins is folate; it is involved in closing the fetal neural tube, which eventually develops into the brain and spinal cord. When folate levels are low, the neural tube cannot close correctly which increases risk for birth defects like spina bifida and can even be fatal. For this reason, women are encouraged to increase their folate intake early in pregnancy or even before they become pregnant. In addition to neural tube defects, low folate levels are related to increased risk for depression1 and anemia2.

It is important to keep in mind that folate (or in fancy science language: 5-methyltetrahydrofolate) and folic acid are slightly but significantly different. Folate can be found in leafy greens (or foliage, hence the name) and legumes. Folic acid is the synthetic version of folate. Many countries add folic acid to grains and cereals. Prenatal vitamins usually include folic acid.

The big difference between the natural and synthetic versions of folate is how they act in the body3. While the natural version of folate can readily act on different biological processes, folic acid cannot. The liver must first metabolize and convert folic acid into folate before it can be used. This extra step is manageable for lower doses of folic acid. However, once folic acid levels get too high, the liver cannot keep up with how much folic acid needs to be converted. This leads to folic acid staying in an unmetabolized form, which is not particularly useful in the cell cycle and may even have adverse effects—although the findings are controversial4. Also, taking a lot of folic acid can make it more difficult for tests to detect if you are deficient in vitamin B12 (it’s important to be able to test accurately for B12 deficiency in order to screen for anemia and neurological dysfunction). Typically, women are advised to take at least 0.4 mg (or 400 mcg) of folic acid but not exceed 1 mg (or 1000 mcg) as this higher dose can mask vitamin B12 deficiency.

For these reasons, keep in mind that while a folic acid supplement is beneficial, eating more folate-rich foods is also necessary to improve folate levels. Alternatively, dietary folate supplements are available (look for L-5-methyltetrahydrofolate) which can increase folate levels equally as well as folic acid5. Unfortunately, due to ethical restrictions surrounding developmental research, there is no clinical evidence that dietary folate supplements have the same preventative effect as folic acid on neural tube defects.

DON’T wait until you’re pregnant to begin taking prenatal vitamins

When is the best time to take prenatal vitamins? For some vitamins, you should begin taking them as soon as you start trying to conceive.

Folic acid/folate is one of these vitamins. As described above, it plays a crucial role in closing the fetal neural tube. The process occurs by the 28th day after conception—before many women even realize they are pregnant. After the first month of conception, increasing folate levels does not prevent these kinds of birth defects.

It is important to increase folate levels before pregnancy to ensure optimal levels of folate are present for the neural tube to close. Currently, women are advised to supplement their diet with 0.4 mg of folic acid at least one month prior to pregnancy (to sufficiently increase the body’s folate levels) and continue taking the supplement until the end of the first trimester.

While it’s not clear whether it’s necessary for pregnant women to continue taking folic acid after the first trimester, it is worth noting that pregnancy demands high levels of folate. Between supporting fetal growth as well as maintaining other biological processes, some pregnant women may be at risk of depleting their own folate stores. Talk to your doctor about whether continuing to take folic acid or folate is right for you.

DO encourage dad to take his vitamins too!

Want-to-be-dads aren’t off the hook! Sperm contribute 50% of the baby’s genetic makeup, so healthy sperm cells are also important for fertility. Interestingly, folic acid seems to be important for fathers as well as mothers. A clinical study found that men with higher folate intake had better quality sperm and fewer genetic abnormalities 6.

In terms of fertility, a review of existing clinical studies found that zinc and folate can increase sperm concentration 7. Also, low folic acid may explain some of infertility problems in overweight and obese men 8. Unfortunately, while basic research points to a more definitive role for vitamins and male fertility, there are relatively fewer clinical studies in male human subjects about how much vitamins play a role in increasing fertility. Regardless, vitamin intake is something for both partners to talk about with their doctors.

DO track your BMI and talk to your doctor about the limitations of prenatal vitamins

Prenatal vitamins have been linked to reduced risk for preeclampsia 9. But, it is important to be aware that pre-pregnancy BMI plays an important moderating role in how prenatal vitamins affect birth outcomes. Two major studies found that regular use of multivitamins around the time of conception significantly reduced risk of pre-eclampsia and preterm birth but only in women with a BMI < 25 and not in women with a BMI > 25 (pre-eclampsia study10; 11.

This means that prenatal vitamins bear different benefits for women of different BMIs. For women who are overweight or have a BMI > 25, it is important to consult with a doctor to monitor weight gain over pregnancy and determine the best prenatal vitamins for you.

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  1. https://www.ncbi.nlm.nih.gov/pubmed/17568057
  2. https://www.ncbi.nlm.nih.gov/pubmed/14960902
  3. https://www.ncbi.nlm.nih.gov/pubmed/23482308
  4. https://www.ncbi.nlm.nih.gov/pubmed/25580388
  5. https://www.ncbi.nlm.nih.gov/pubmed/12081832
  6. https://www.ncbi.nlm.nih.gov/pubmed/18353905
  7. https://www.ncbi.nlm.nih.gov/pubmed/28853101
  8. https://www.ncbi.nlm.nih.gov/pubmed/29313750
  9. https://www.ncbi.nlm.nih.gov/pubmed/12730485
  10. https://www.ncbi.nlm.nih.gov/pubmed/12730485
  11. https://www.ncbi.nlm.nih.gov/pubmed/21795441

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