What you need, what you don’t, what we don’t know
by Tara HaelleWhether it’s chewables, gummies or those big, nasty things you have to swallow, prenatal vitamins can vary in more than just how you take them. They also vary in what they have to offer. The question is whether what they offer is what you actually need, while conceiving, while pregnant, or while breastfeeding. The reality is that most of the nutrient recommendations issued by ACOG, WHO or other organizations are not based on firm evidence. We know some things from the research, but there is far more we don’t know. In fact, about the only thing we’re pretty sure of is that the most important nutrient in pregnancy is folate, from conception through the first trimester. After that, the benefit-harms ratio of supplements gets fuzzier, in part because women in the developed world likely already get the bulk of what they need from their diet. And getting more may not be better.
Vitamins and minerals are an essential part of metabolism and serve a variety of functions, so deficits can certainly cause health problems, such as scurvy (inadequate vitamin C), rickets (inadequate vitamin D), and anemia (inadequate iron). But too much of a good thing can be a not-so-good thing, even with vitamins and minerals. In fact, taking too much of some vitamins may actually be harmful. For example, reviews of studies on vitamins A and E and beta carotene have found links between very high doses of these vitamins and some cancers, vascular disease, heart failure and diabetes. The amounts are generally much more than would be found in a daily multivitamin, but if you’re taking supplements, it’s important to be aware of what amounts you’re getting from the various things you’re taking.
None of these studies necessarily mean the vitamins are causing the problems, but the excess vitamins aren’t helping either. How might vitamins go from helpful to harmful, if that’s what’s happening? Consider how food is metabolized. The mitochondria in your cells use oxygen to convert food into energy, a process called oxidation that releases free radicals. Free radicals are as destructive as political radicals: they wreak havoc on DNA, cell membranes and your artery linings, which can increase the risk of cancer, heart disease and aging. That’s why it’s necessary to get antioxidants like selenium, beta carotene and vitamins A, C and E in foods – they zap the free radicals. Yet free radicals also wreak havoc on bad bacteria and new cancer cells. The body needs a healthy balance of both free radicals and antioxidants, lest too much of the latter leave the body vulnerable to the bad guys getting killed by free radicals. This hypothesis is not settled science, but it’s possible that it plays a role in ways antioxidant supplements might cause problems.
So far, there is no evidence that supplemental B vitamins or other antioxidants besides those above could be harmful, but there is also no evidence they prevent chronic illness or have any other benefits when taken as supplements.
Unless you’re pregnant. Kind of.
Pregnant and breastfeeding women do require more of some vitamins and minerals than adults who aren’t growing a little human, but the principle still holds that going overboard can cause problems both for the woman and for the little human. For most vitamins and minerals, pregnant women only need a little more – if any additional at all – than what they need while not pregnant, and lactating women typically need the same or slightly more than pregnant women. But most of this can be consumed through a healthy, balanced diet, especially since the increased amounts for each vitamin or mineral aren’t that much and since many foods are fortified with extra nutrients needed during pregnancy, such as folic acid, iron, iodine, and vitamin D. Plus, as I noted, there is little evidence on the benefits of supplementation in women in the developed world. So, does that mean you can skip the prenatal? Or should you take on? And which one? I’ll revisit these questions after reviewing the evidence on a handful of specific nutrients.
The Most Important Prenatal Vitamin
Despite all that we don’t know, there’s little uncertainty about folate. Found in asparagus, Brussels sprouts, oranges, nuts, beans, peas, and green, leafy vegetables, folate, or vitamin B9, is, without a doubt, the most important nutrient a pregnant woman needs. Folate, either from dietary sources or from folic acid chopped up in the body, is converted into a useable form for helping cell division and building DNA and other genetic material. Chemically synthesized folic acid (the acidic form of folate) is stable in the solid form and therefore what’s included in supplements.
What makes this nutrient so essential is its role in development of the nervous system. Sufficient folic acid in the first month of embryonic development prevents defects in the neural tube, which forms by the 28th day after fertilization and develops into the brain and spinal column. It may also reduce the risk of preterm birth and birth defects, but the data are less clear on this. Insufficient amounts of folic acid can contribute to neural tube defects such as spina bifida and anencephaly.
The problem, of course, is that many women – especially those with unplanned pregnancies, comprising about half of all pregnancies each year – don’t know they’re pregnant in that first month. By the time they know, it’s usually too late to affect neural tube formation. Therefore, the US Preventive Services Task Force recommends that women who could become pregnant take a daily supplement of 400 to 800 ug above and beyond the folate they get from food. To address potential deficiencies in women not getting enough, folic acid has been added since 1998 to enriched bread, cereal, flour, cornmeal, pasta, rice, and other grain products. Within a year or two of this federally mandated fortification of grain products, births with neural tube defects declined approximately 20 to 30 percent.
So far, no data shows high intake of dietary folate to be harmful, and there is little practical difference between folate and folic acid other than slightly different rates of absorption. However, 1000 mcg is considered the safe upper limit for taking folic acid supplements because too much may mask symptoms of vitamin B12 deficiency, which, ironically, can cause brain, spinal cord and nerve damage to the person taking it. Too much folic acid has also been linked to increased rates of breast cancer risk in postmenopausal women and of lung cancer and death in heart disease patients, but we’re talking about very high amounts in special populations (and postmenopausal women, by definition, cannot become pregnant and don’t need the extra amount anyway).
To get a Goldilocks dose of folic acid – not too much and not too little – a balanced diet and possibly supplements of 600 mcg should get you within range. If you’re on a special diet, consider how that affects your intake. For example, I was on a very low-carb diet when I was trying to conceive. On the one hand, I wasn’t eating some of the very foods, such as grains, that are supplemented with folic acid. On the other hand, I was eating more of the foods, such as spinach and broccoli, that contain naturally high levels of folate.
Iron and Iodine
Iron is essential for making hemoglobin, which carries oxygen in red blood cells, and myoglobin, which carries oxygen in muscle cells. Insufficient amounts can lead to fatigue and anemia, which has been linked to low birth weight, preterm birth and prenatal depression. Because women have a greater blood volume while pregnant, they need more iron, a recommended 27 mg instead of 18 mg. Most people are aware that red meat, such as beef, is rich in iron, as is poultry, liver, tuna and salmon. But for those who limit their red meat or are vegetarians, iron is also available in whole grains, iron-fortified cereals, dried beans, dried fruits, and egg yolks. The consensus in the research is that iron supplements reduce the risk of anemia, iron deficiency, and low birth weight. However, side effects of too much iron include constipation, nausea, vomiting, diarrhea, and pregnancy complications due to high hemoglobin, and taking vitamin C increases iron absorption. Most routine prenatal care involves checking iron levels.
Iodine is essential for both thyroid hormone production and normal brain development in the fetus. Women need about 50% more iodine when pregnant to prevent problems with fetal neurological development. Since the 1920s, when iodized salt arrived on the scene, iodine deficiency hasn’t usually been a problem for most people, but pregnant women may get insufficient amounts if they eat a lot of processed foods, which don’t use iodized salt, or if they don’t use much iodized salt themselves. Other dietary sources include seafood, seaweed, and dairy and grain products. Supplemental iodine – which more than half of all prenatal vitamins don’t include – has been shown to improve birthweight, infant mortality and cognitive developmental of children… in areas with moderate to high iodine deficiencies.
However, a 2014 statement from the American Academy of Pediatrics noted concerns about insufficient iodine levels in pregnant women in the US, based on recent data that some pregnant women aren’t getting enough, especially those who don’t eat much dairy. Although the evidence isn’t there to recommend it for all women in the developed world, there is enough to say a supplement might be a good idea if you’re pregnant and getting less than the recommended 220-250 mcg a day (or 250-290 mcg a day while breastfeeding), guidelines supported by the American Thyroid Association, the National Academy of Sciences and the Institute of Medicine. However, iodine is also one of those goldilocks supplements where you need to be sure not to get too little or too much: excess iodine intake can cause thyroid problems for the developing fetus. What’s too much? About 500 mcg a day, though even that guideline is based on weak evidence.
The Enigma of Vitamin D
Oh vitamin D, the most enigmatic – and currently fashionable – of vitamins. It seems everyone has something to say about this nutrient – what’s too little, what’s too much, how much we should supplement, what too much or too little can cause – but in reality, we don’t have a lot of reliable evidence from which to draw any of these conclusions. The daily recommendation is 5 mcg (200 IU), or 400-600 IU depending on who you ask, but this is not based on evidence. The Institute of Medicine has set a safe upper limit at 4,000 IU per day, but this is also not based on clear evidence – and some scientists recommend supplementing with more than double that – again, without solid evidence. Vitamin D helps maintain bone health and calcium levels in the body, and we know severe deficiencies can cause rickets, but there isn’t agreement on what inadequate levels or deficiency during pregnancy is. (The Institute of Medicine says levels than 12 ng/ml, or 30 nmol/L put someone at risk for deficiency.) Even so, one study found up to 11% of US women are vitamin D-deficient and up to 26% have inadequate levels.
Some systematic reviews have linked blood levels below 50 nmol/l to an increased risk of pre-eclampsia, gestational diabetes, preterm birth, small-for-gestational age babies, bacterial vaginosis, and, to a lesser extent, an increased risk of C sections, slightly shorter gestations, and postpartum depression; others found too little evidence for any of this, and none of the studies established that too little vitamin D causes anything. In fact, a Cochrane review found that vitamin D supplements during pregnancy – despite increasing vitamin D levels in women – did not prevent pre-eclampsia, gestational diabetes, C sections, gestational hypertension, preterm birth or any poor outcomes with newborns. So great, the women’s levels increased, but what difference did it make?
Whether women should take vitamin D supplements during pregnancy is unclear, and it may depend on skin pigmentation of your skin, sunlight exposure and physiological differences among women. But you can up your intake through your diet from fatty fish, liver, mushrooms, egg yolks, some cheeses, and fortified milk, yogurt, cereals, and fruit juices. It doesn’t take much sun to boost your levels either: 5 to 30 minutes any time mid-morning to mid-afternoon. To protect yourself from burns and skin cancer risk, know that sunscreen does allow some vitamin D synthesis in the skin.
The Rest of the Alphabet
Again, most of the evidence isn’t there to recommend most other nutrients. Calcium supplements can help reduce the risk of pre-eclampsia, primarily for women not getting enough calcium through dairy products, and zinc supplements might very slightly reduce preterm birth risk if women are deficient. Vegetarians may be at risk for vitamin B12 deficiency. There’s no evidence or not enough evidence to see better newborn or pregnancy outcomes for taking extra vitamin B6, vitamin E, magnesium, or vitamin C, and extra vitamin E may have risks, though data are weak.
Most Americans already get sufficient selenium daily through meats, fish, grains, cottage cheese, and eggs, and too much extra selenium can increase the risk of type 2 diabetes. Vitamin A supplements reduce anemia in women where deficiency is common (or in HIV positive women), but too much vitamin A during pregnancy (more than 10,000 IU a day) can cause birth defects. Since most prenatals have 4,000 to 5,000 IU, it’s definitely not necessary to take supplemental vitamin A if you take a prenatal.
So, Pop a Prenatal or What?
Which brings us full circle to that question: should you take a prenatal? Unfortunately – other than the recommendation to take folic acid – there is no general recommendation that can be made for all women on this question.
Some findings estimate that 20% to 30% of pregnant women have some sort of vitamin deficiency, but the specifics vary from one woman to the next, and these are deficiencies across the world, including women in developing countries. Major deficiencies of any nutrient can certainly cause problems during pregnancy or for the fetus or newborn, but “deficiency” is a clinically diagnosed condition by a doctor (not something people can generally determine on their own), and these deficiencies don’t tend to occur in developed countries where balanced diets take care of the needs of healthy individuals without special medical conditions.
The only benefit seen in the research for prenatal vitamins is a moderately reduced risk of low birth weight and underweight (small-for-gestational-age) babies, but, again, only for women in lower income countries, where known nutrient deficiencies exist. We don’t have studies showing improved birth outcomes for women in developed countries taking prenatals, and most women in the U.S. probably don’t need them.
Then why do clinicians recommend them? They are likely working off a better-safe-than-sorry mindset given that women’s diets vary so dramatically and many likely have poor diets. It is impossible to create nutrient supplement guidelines to apply to all individuals, or even most. People vary too much in terms of their diet, their physiology, their size, their activity level, and other key factors that will influence their nutrient needs.
Further, the risks of taking a single daily prenatal are low because the amounts are calibrated to be approximately what extra amounts a pregnant woman needs to stay within the Institute of Medicine’s recommended daily amounts. In addition to the vitamin A risks noted above (only if women are taking another supplement containing high levels of vitamin A – such as cod liver oil – on top of a prenatal), the biggest other risk for a combined prenatal vitamin supplement is nausea, which can usually be addressed by taking them at night instead of morning.
What do I look for in selecting a prenatal?
If you decide to take a prenatal, look at how much of each vitamin and mineral is included and what you may not be getting from your diet that you need the prenatal to provide. Most prenatal vitamins are pretty similar in terms of the basic they offer, but about half do not include iodine, which is one of the key nutrients pregnant women may be more likely to need. One way to determine for yourself which nutrients you personally might need – besides folic acid, which all pregnant women need – is to keep a detailed diet diary for at least three days and then see how your diet compares to the requirements using the tool at https://www.supertracker.usda.gov/
Another consideration is that vitamins are not regulated as strictly as medications. Brands containing a “USP Verified Mark” seal have voluntarily been inspected by the U.S. Pharmacopeial Convention, a scientific nonprofit, and have met four key requirements:
- The supplements contain the ingredients listed at the amounts listed on the label
- The supplements do not contain harmful levels of contaminants
- The nutrients will be absorbed and metabolized in the body soon enough (they don’t do you much good if you just pee out what you’ve taken)
- The products have been manufactured in sanitary, controlled environments
And if you do decide to take one, keep in mind that taking any additional supplements on top of the prenatal may put you above the targets, and too much of a good thing isn’t always good.