Benefits and risks of vitamins and minerals consumed during pregnancy
Introduction
Healthy lifestyle and nutrition are mentioned in scientific literature as an indisputably important factor for the health of a pregnant woman and the future baby. Many changes occur in a pregnant woman's body, increasing not only the need for basic nutrients such as proteins, fats, and carbohydrates but also for vitamins and micronutrients. During pregnancy, even with a balanced diet, there may be a deficiency of important vitamins and micronutrients for fetal development, such as folic acid, vitamins B and D, omega-3 fatty acids, iron, calcium, iodine, etc. Darnton-Hill and colleagues described that a deficiency of micronutrients can epigenetically affect gene expression, which regulates fetal development, and increase the risk of chronic diseases in adults (1).
According to other sources, inadequate nutrition, lack of vitamins, and micronutrients cause changes in fetal metabolism, which not only affect the course of pregnancy but also increase the likelihood of metabolic diseases such as diabetes later in life because fetal metabolic programming occurs (3). A woman's nutritional status is important even before conception. Therefore, it is essential to inform women planning pregnancy and those already pregnant about the importance of a balanced diet, the benefits of essential vitamins and minerals, and possible harm.
Folic Acid
Folic acid is a synthetic analogue of B vitamin found in nature (7). It is involved in the biosynthesis of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), homocysteine and amino acid metabolism (8). Homocysteine contributes to vascular wall damage and the development of atherosclerosis (4). Research data shows that homocysteine concentration in the blood depends on diet, genetic factors, and the concentration of vitamins B and folic acid in the blood - the lower the levels of these vitamins in the blood, the higher the homocysteine concentration (4).
A deficiency of folic acid during pregnancy is associated with an increased risk of megaloblastic anemia but does not increase the risk of premature birth (9). The lack of this substance is related to neural tube defects, anemia, delayed intrauterine growth, low birth weight, and an increased risk of coronary heart disease, myocardial infarction in later stages of the baby's life (4). The need for folic acid during pregnancy greatly increases due to accelerated cell division, increased cell numbers, and fetal growth (7). The consumption of folic acid even before pregnancy significantly reduces the risk of neural tube closure defects. Observations show that increased intake of folic acid before and during pregnancy significantly decreases the frequency of neural tube closure defects (6). By taking folic acid, the incidence of neural tube defects decreases by up to 46% (4).
Healthcare providers recommend that pregnant women consume foods rich in folates, such as bread, grains, citrus fruits, leafy green vegetables, and nuts. They advise all women planning pregnancy to start taking folic acid supplements before conception and continue until the 12th week of pregnancy. The World Health Organization (WHO) recommended daily dose of folic acid is 400 µg (16). According to other sources, the daily dose of folic acid can vary from 400 to 800 µg, further increasing the dose for women who had a neural tube closure defect observed in previous pregnancies (7).
Vitamin B Complex
B vitamins participate in regulating metabolism, help reduce insulin resistance, and are essential for the development of the nervous system, neural tube closure (6). Vitamin B6 (pyridoxine) is involved in amino acid metabolism and is a catalyst for many reactions, such as neurotransmitter synthesis. Vitamin B6 helps reduce nausea. This vitamin is abundant in meat (beef, pork, chicken), fish (tuna, salmon), oats, bananas, prunes, avocados, and potatoes. Additional intake during pregnancy is not necessary (3). The WHO recommended daily allowance for pregnant women is 1.9 µg (4).
Vitamin B12 (cobalamin) participates in various metabolic enzyme reactions and is necessary for the synthesis of the amino acid methionine and tetrahydrofolate (metabolite of folic acid). Vitamin B12 is abundant only in animal products: meat (especially beef), dairy and its products, fish. This vitamin, along with folic acid, is necessary for the intellectual and motor development of the fetus. Women who have had stomach surgeries or are vegans may have a vitamin B12 deficiency, so they should take supplements during pregnancy. For other women, supplement intake is not necessary (3). The WHO recommended daily allowance for pregnant women is 2.6 µg (4).
Vitamin D
Vitamin D - a fat-soluble vitamin found in milk or juice. Naturally, vitamin D is abundant in eggs and fish (e.g., salmon). Some of this vitamin is produced in skin cells during sun exposure. Regardless of whether this vitamin enters the body exogenously (with food) or endogenously (produced in the body), its further metabolism in the liver and kidneys is necessary to form the active form of vitamin D - 1,25-dihydroxycholecalciferol, also called calcitriol. It promotes calcium absorption from the intestines, while calcium ensures healthy bone mineralization and growth.
Deficiency is very often detected, especially in women who follow a vegan or vegetarian diet, live in a cold climate zone. Lithuania is classified as a high-risk zone for vitamin D deficiency, so women who do not take supplements have a 47% higher risk of developing a deficiency in this vitamin in the summer and a 69% higher risk in winter. Overweight women are classified as a higher risk group for vitamin D deficiency because their bodies naturally require more of this vitamin, not only during pregnancy.
Vitamin A
Is vital for cell differentiation and proliferation, spine, heart, eye, and ear development. Vitamin A deficiency is a rare phenomenon, however, newborns of mothers who lacked vitamin A during pregnancy have been observed to have higher mortality, which may be related to immune system defects. Although most safe dose intervals for micronutrients are wide, vitamin A is an exception. High daily doses of vitamin A (>10,000 IU) are associated with craniofacial (facial, ear, cleft) and congenital heart defects. Only the vitamin A form retinol is associated with teratogenic (harmful to fetal health) effects. Carotenoids found in food products do not have this effect. Therefore, pregnant women are recommended not to exceed more than 8,000 IU/day of vitamin A.
Omega-3 Fatty Acids
Omega-3 fatty acids are necessary for fetal brain development and are associated with better visual function in preterm infants, better cardiovascular health in infants as they grow. EPA and DHA acids are particularly important. EPA maintains good heart, immune system function and acts on the inflammatory response, while DHA ensures good central nervous system and visual functions.
Omega-3 fatty acids are involved in balanced prostaglandin production. The latter are involved in the body's inflammatory response, blood pressure, clotting system, and nerve impulse transmission. EPA and DHA are abundant in fatty fish such as salmon, sardines, mackerel. However, pregnant women should not eat fish more than twice a week (portion size - 140 g), as certain species contain more harmful mercury. Fish with the highest mercury content are shark, swordfish, king mackerel, tilefish, and marlin. It is not recommended to eat these types of fish during pregnancy. Pregnant women who do not eat fish are recommended to supplement their diet with fish oil containing omega-3 fatty acids, but it is important to pay attention to the composition of fish oil.
Iron
Iron needs during pregnancy greatly increase in the second half of pregnancy. It is necessary to ensure adequate fetal blood circulation and oxygen transport. During pregnancy, it is recommended to eat a lot of iron-rich foods such as red meat, eggs, nuts, green leafy vegetables, and dried fruits. Vitamin C helps absorb iron, so after taking an iron supplement or after a meal, it is recommended to drink citrus fruit juice. Coffee and tea reduce iron absorption, so it is not advisable to drink them with the main meal. Women diagnosed with iron deficiency may have symptoms of anemia, and laboratory blood tests may show a low ferritin concentration.
Calcium Requirements During Pregnancy
Calcium, like other micronutrients, has increased requirements during pregnancy. Throughout pregnancy, the fetus absorbs about 30 g of calcium, with 25 g deposited in the bones. Calcium is extremely important for the development of the fetal bones and maintaining good maternal skeletal function.
Benefits and Risks of Calcium Supplements
The use of calcium supplements during pregnancy reduces the risk of preeclampsia and hypertension. However, these women were found to have a higher risk of HELLP syndrome (HELLP - hemolysis, elevated liver enzymes, low platelet count). Calcium intake had no effect on the increase in eclampsia or maternal mortality risk. It also did not increase the risk of preterm birth or low birth weight (17).
Calcium Absorption and Vitamin D
The absorption of this micronutrient significantly increases during pregnancy. However, calcium absorption depends on the active vitamin D levels in the body, so it is important to avoid a deficiency of this vitamin.
Dietary Sources of Calcium
Calcium that is easily absorbed is abundant in dairy products such as milk, kefir, yogurt, cheese, and cottage cheese. A glass of milk or 200 g of cottage cheese contains 300 mg of calcium. It is better to choose natural yogurt to avoid excessive sugar consumption. For women who are lactose intolerant, it is recommended to choose soy milk, almonds, or calcium-fortified oats (3).
WHO recommends calcium supplements for pregnant women who consume low-calcium foods or those who have hypertension, increasing the risk of preeclampsia. The recommended daily dose is 1.5-2 g (17).
Iodine
Iodine is a vital micronutrient because the pregnant woman's body uses it to produce thyroid hormones. These hormones are essential for the normal development of the fetal central nervous system, as well as cognitive and behavioral functions. Iodine deficiency is one of the preventable causes of impaired mental and behavioral functions in the fetus. The fetus is most sensitive to iodine deficiency in the early months of development, so women should start taking iodine supplements before conception or in the early weeks of pregnancy.
Women should consume 150-250 µg of iodine daily to achieve this. A pregnant woman can safely take a maximum dose of 600 µg of iodine per day. Doses greater than 1,100 µg are unsafe. Women with impaired thyroid function should consult an endocrinologist for an appropriate higher dose of iodine (3). WHO recommends that pregnant women living in countries with poor access to iodized salt or where an iodized salt program is not implemented take iodine supplements (19). In such cases, pregnant women should take 250 µg of iodine per day (4).
Iodine can be obtained from food by eating fish, seafood, and dairy products. However, even with a healthy diet that includes iodized salt in cooking, seafood at least twice a week, and daily dairy products, one can only get up to 100 μg of iodine. Therefore, the body requires an additional 100-150 μg of iodine from dietary supplements. During pregnancy, seaweed or kelp preparations are not recommended as they can cause iodine overdose, disrupting thyroid function (3).
Vitamins C and E, Magnesium, Zinc
Vitamin C (ascorbic acid) is an important antioxidant involved in collagen synthesis. During pregnancy, vitamin C intake needs to be increased by 10 g/d, but this requirement should be met through diet.
Vitamin C is abundant in cabbage, tomatoes, peppers, broccoli, strawberries, pineapples, black currants, kiwis, and citrus fruits.
Vitamin E (tocopherol) is a member of the antioxidant group, entering the fetal bloodstream only by the 12th week of pregnancy. Although vitamin E deficiency is very rare, excessive intake can be a greater concern. Various studies associate excessive vitamin E with birth complications and a higher likelihood of developing cardiovascular disease later in the child's life. Plant oils such as olive, sunflower, and rapeseed, as well as egg yolks, nuts, and seeds (pumpkin, sunflower, sesame), are rich sources of vitamin E (3).
The fetus accumulates 1 g of magnesium daily, and a woman's magnesium needs are usually met through diet (3). Magnesium supplements are recommended for women experiencing muscle cramps (2). Magnesium is abundant in nuts, whole grains, and green leafy vegetables (3).
A lack of zinc does not immediately activate the release of zinc from the reserves in a pregnant woman's skeletal system, so a deficiency of this micronutrient can develop suddenly. Rarely, this can increase the risk of congenital deformities and brain function disorders (10). Zinc sources include red meat, seafood, and whole grains (3). According to scientific research, the administration of zinc supplements to pregnant women does not improve the health of newborns compared to women who are not given zinc supplements (10).
A deficiency of all the micronutrients and vitamins mentioned in this paragraph during pregnancy is very rare, and any developed deficiency is compensated for by diet, so there is no need to take supplements of these substances (3). The recommended daily allowances of these and other key vitamins and micronutrients for pregnant women by WHO are presented in Table 1.
Table 1. WHO recommended daily allowances of vitamins and micronutrients for pregnant and lactating women (4)
| Vitamin or Micronutrient | WHO Recommended Daily Allowance |
| Vitamin A | 800.0 µg |
| Vitamin B1 (thiamine) | 1.4 mg |
| Vitamin B2 (riboflavin) | 1.4 mg |
| Vitamin B3 (niacin) | 18.0 mg |
| Vitamin B6 (pyridoxine) | 1.9 mg |
| Vitamin B12 (cobalamin) | 2.6 µg |
| Vitamin C (ascorbic acid) | 5.5 mg |
| Vitamin D | 5.0 µg |
| Vitamin E (tocopherol) | 15.0 mg |
| Folic acid | 600.0 µg |
| Iron | 27.0 mg |
| Zinc | 10.0 mg |
| Copper | 1.15 mg |
| Selenium | 30.0 µg |
| Iodine | 250.0 µg |
| Calcium | 1.5–2.0 g |
Unsafe or harmful substances
Discussing the necessary vitamins and micronutrients for healthy fetal development, it is important to mention several substances not recommended by the WHO. These include lead, excessive vitamin A, and mercury.
Lead is a heavy metal harmful to everyone, not just pregnant women. If there is significant contact with lead-containing food storage containers or cookware with worn-out Teflon coating, lead can cross the placental barrier and reach fetal tissues. Lead exposure is associated with increased risks of hypertension, spontaneous abortion, and low birth weight (3).
To avoid vitamin A overdose, pregnant women should avoid consuming large amounts of animal liver, products rich in retinol (e.g., fish oil). Plant-based products high in carotene are a better choice as carotene is non-teratogenic.
Mercury is a substance that accumulates in the flesh of large ocean fish (e.g., sharks, tunas, swordfish, king mackerel, tilefish). Pollution in the Baltic Sea is increasing, so pregnant women are advised against eating fish caught in this sea. Furthermore, mercury also accumulates in freshwater fish - European pikeperch, perches, and roaches. However, only pikeperch should be avoided (recommended to eat only once a week). It is recommended not to consume more than 140 g of tuna per week (3).
Recommendations for the intake of vitamins and micronutrients for pregnant women worldwide and in Lithuania
There is much discussion about which vitamins and micronutrients all pregnant women need to take, and which ones should only be taken if a deficiency is detected. In the Healthy Mother's Nutrition During Pregnancy Planning and Pregnancy Guidelines issued by Latvian doctors and WHO specialists in 2016, it is mentioned that during pregnancy, the following supplements should be taken:
• iodine - 150 µg/day before and during pregnancy;
• 400 µg/day - folic acid, starting before pregnancy and continuing until the 12th week of pregnancy;
• 20 µg/day vitamin D in winter;
• iron supplements only if there are indications (e.g., anemia);
• omega-3 fatty acids if the pregnant woman does not eat fish (3).
The Lithuanian Association of Obstetricians and Gynecologists and the Lithuanian Society of Obstetricians and Gynecologists have approved the document on Antenatal Care in the obstetric methodology, which recommends/not recommends the intake of these micronutrients and vitamins during pregnancy.
Recommended:
• 400 µg of folic acid per day. It is best to start 3 months before pregnancy and continue until the 12th week of pregnancy;
• 10 µg (400 IU) of vitamin D per day for pregnant women who spend little time outdoors, in the sun, consume fewer foods containing this vitamin;
• calcium supplements are given when the pregnant woman consumes few dairy products (less than 4 servings per day), is at risk of pregnancy-induced hypertension;
• iron is given if iron deficiency is detected;
• multivitamins are given to pregnant women with inadequate nutrition, at higher risk of preterm birth, or whose fetal growth is delayed.
Not recommended:
• excessive vitamin A intake, so supplements containing more than 700 µg of this vitamin, liver products, pate should be avoided;
• magnesium is not recommended if there is a risk of miscarriage or preterm birth. Magnesium is prescribed for muscle cramps (2).
Conclusions
Most pregnant women in this era of information overload are well aware that during pregnancy, it is necessary to eat healthily and fully, be physically active, and avoid harmful habits such as smoking or alcohol consumption. However, only a small percentage of them have heard about the increased need for vitamins and micronutrients during pregnancy and which of them are extremely important for fetal development, while excessive intake can harm the fetus. It is important to emphasize the importance of certain vitamins and micronutrients to women who are pregnant or planning to conceive.
Publication "Internist" No. 8 2018
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Justina Rauluševičiūtė
