The developing baby in the womb is completely dependent on its mother for its nutrient supply, so the quality of the maternal diet is extremely important. During pregnancy, increased intake is required of several nutrients, such as vitamins A, B1, B2, C and D and folate (Table 1). Women's absorption of certain nutrients increases during pregnancy, which can help achieve adequate nutrient levels (Department of Health (DH), 1991). Despite this, the dietary intake and/or stores of key nutrients (e.g. vitamin D) are often found to be low in pregnant women (McAree et al, 2013). Supplements of folic acid and vitamin D are recommended around pregnancy, as diet alone is unlikely to be able to provide a sufficient supply (DH, 1991).
| Nutrient | Reference nutrient intake (RNI) | Current picture among women | Practical messages | Dietary sources | ||
|---|---|---|---|---|---|---|
| Women aged 19–50 | Pregnant women | Breastfeeding women | ||||
| Vitamin A (retinol) | 600 µg | +100 µg | +350 µg | 5% of women aged 19–64 have vitamin A intake below the LRNI; 14% of adolescent girls (aged 11–18) have intakes below the LRNI1 | Liver is a particularly rich source of vitamin A, but too much vitamin A can harm the unborn baby. Liver and liver products should not be eaten more than once a week, and should be avoided by pregnant women2 | Cheese, butter, margarine, reduced-fat spreads. Carrots, dark-green leafy vegetables and orange-coloured fruits provide beta-carotene, which the body can convert to vitamin A |
| Vitamin B1 (thiamin) | 0.8 mg | +0.1 mg (last trimester only) | +0.2 mg | Current average daily intake among adult women aged 19–64 is 1.28 mg1 | Vitamin B1 cannot be stored in the body, so a daily intake is required | Wholegrains, nuts, meat (especially pork), fruit, vegetables, fortified breakfast cereals |
| Vitamin B2 (riboflavin) | 1.1 | mg +0.3 mg | +0.5 mg/day | Around 12% of women aged 19–64 have average daily vitamin B2 intakes below the LRNI3 | Many women get most of their vitamin B2 from animal sources, particularly dairy foods, so if they avoid these foods it is important that they include non-animal sources of vitamin B2 | Milk, eggs, fortified breakfast cereal, legumes (peas, beans, and lentils), mushrooms, green vegetables, almonds |
| Vitamin B3 (niacin) | 13 mg | No increase | +2 mg | Current average daily intake among adult women aged 19–64 is 31.6 mg1 | Vitamin B3 can be synthesised from the essential amino acid tryptophan to meet daily requirements. Dietary intake is only necessary when tryptophan metabolism is disturbed, or intake is inadequate | Meat, wheat and maize flour, eggs, dairy products, yeast |
| Vitamin B12 (cobalamin) | 1.5 µg | No increase | +0.5 µg | Current average daily intake among adult women aged 19–64 is 4.6 µg1 | Vegan diets, and some vegetarian diets that contain only small amounts of dairy products and eggs, are likely to be lacking in vitamin B12 | Milk, eggs, fortified breakfast cereals, legumes (e.g. peas, beans, and lentils), mushrooms, green vegetables |
| Folate* | 200 µg | +100 µg | +60 µg | Average intake among UK women aged 19–24 is 248 µg/day, and for women aged 25–34 is 249 µg/day3. |
Evidence suggests folate levels in breast milk are maintained at the expense of maternal folate reserves, so it is important for breastfeeding women to include plenty of foods containing folate/folic acid to maintain supplies | Green leafy vegetables, peas, potatoes, oranges, melon, bananas, beans, wholegrain products, nuts, fortified breakfast cereals |
| Vitamin C (ascorbic acid) | 40 mg | +10 mg (last trimester only) | +30 mg | Current average dietary intake among women aged 19–64 is 81.6 mg1 | During pregnancy there is a moderate extra drain on the mother's stores, especially in the final trimester. The increased RNI ensures maternal stores are maintained and breast milk levels are adequate | Fresh fruit (especially citrus fruits and berries), green vegetables, peppers, tomatoes, potatoes (especially new potatoes) |
| Vitamin D | No RNI | +10 µg | +10 µg | Current average dietary intake among women aged 19–64 is 2.6 µg1 | The main source of vitamin D is through the action of sunlight on the skin. About 10–15 minutes of skin exposure to the sun is enough for most lighter-skinned people to obtain adequate vitamin D2 | Oily fish, eggs, fortified foods including breakfast cereals, some fortified dairy products and reduced-fat spreads |
LRNI–lower reference nutrient intake
Women who are breastfeeding require even more nutrients than when pregnant (DH, 1991). Increased amounts of the aforementioned vitamins—along with vitamins B3 and B12—are required when breastfeeding. Adequate levels of these vitamins, with the exception of vitamin D, can be obtained by eating a healthy, varied diet. As in pregnancy, a daily supplement of vitamin D is required for breastfeeding women.
Reference nutrient intakes (RNIs) for vitamins are an estimate of the amount that should meet the needs of most of the group to which they apply. They are not minimum targets. Intakes that fall below the lower reference nutrient intake (LRNI) are almost certainly not enough for most people; this is a useful measure of nutritional inadequacy.
This article discusses key nutrients of importance during pregnancy and breastfeeding: folate/folic acid, vitamin D, vitamin A and vitamins B2 and B12.
Folate/folic acid
Folic acid is the name given to the synthetic form of the B vitamin know as folate. The RNI of folate for women aged 19–50 is 200 µg. Folate (or folic acid) is needed to prevent neural tube defects (NTDs) in babies. A baby's central nervous system (brain and spinal cord) normally develops first as a flat sheet of cells (the neural plate) which rolls up (the neural tube) in weeks 3–4 of pregnancy and closes to form the central nervous system. NTDs, such as spina bifida, may result when the tube does not close properly. The neural tube forms in the early weeks, before many women realise they are pregnant. Since the early 1990s, it was evident that consumption of folic acid (400 µg per day) around the time of conception could reduce the risk of NTDs in babies (Medical Research Council, 1991).
The UK government advises women who may become pregnant to take a daily folic acid supplement of 400 µg, continuing up to the 12th week of pregnancy, and to consume foods providing folate/folic acid in the diet. Such foods include green salads, peas, broccoli, Brussels sprouts, cabbage, cauliflower, parsnips, spinach, tomatoes, oranges, chickpeas, wholemeal bread and fortified breakfast cereals.
The additional requirement for folate (the form of the vitamin found naturally in foods) throughout pregnancy (+100 µg) and breastfeeding (+60 µg) can be provided by a diet containing folate-rich foods. As significant amounts of folate cannot be stored in the body, a daily dietary supply is important. Folate is one of the nutrients commonly found to be low in the diets of breastfeeding women (Lennox et al, 2013). The current average folate intake among all women aged 19–64 years is 228 µg (Bates et al, 2014), which is just above the non-pregnant RNI of folate. Evidence suggests that folate levels in breast milk are maintained at the expense of maternal folate reserves in the liver and circulating round the body (Hausner et al, 2008). While this protects the infant, the nutrient status of the mother and the impact on subsequent pregnancies would be of concern. Breastfeeding women should consume plenty of foods containing folate and folic acid to ensure adequate levels are maintained.
Women who have already experienced an NTD-affected pregnancy are advised to take a 5 mg folic acid supplement daily (Scientific Advisory Committee on Nutrition (SACN), 2013) and it has been suggested that obese women should also take a 5 mg dose of folic acid daily from before pregnancy until the first trimester (Centre for Maternal and Child Enquiries (CMACE) and Royal College of Obstetricians and Gynaecologists (RCOG), 2010). This is to help minimise the risk of NTD-affected pregnancies, which are more prevalent among women with a body mass index (BMI) of >30 (CMACE and RCOG, 2010). Women with pre-existing diabetes also require 5 mg folic acid (Kennedy and Koren, 2012).
Although awareness of the need to take folic acid appears to be high, compliance with this recommendation is not necessarily reflected in practice. In a study in Northern Ireland, 84% of the 296 women reported taking folic acid supplements in the first trimester, but only 19% had started before conception (McNulty et al, 2011). As around half of all pregnancies in the UK are unplanned (SACN, 2013), health professionals such as GPs, nurses and pharmacists have a key role in raising awareness of the importance of folic acid in preventing NTDs among women of childbearing age.
Vitamin D
Vitamin D helps the body absorb calcium from the diet, which is important for healthy bones. There is also evidence that vitamin D may help protect against diabetes, cardiovascular disease and some cancers, as well as optimising immune function (Buttriss et al, 2013). During pregnancy, vitamin D is important for the development of the baby's bones and teeth. The main source of vitamin D is through the action of sunlight on the skin during the summer months. Achieving adequate vitamin D levels is, therefore, more challenging in the winter months and for women who cover up their skin when outdoors, along with women who have darker skin, such as those of African, Afro-Caribbean or South Asian origin. Also at particular risk of low vitamin D status are those who avoid animal foods or who have a very poor diet (Crawley, 2014).
There are few dietary sources of vitamin D, but oily fish—including salmon, mackerel, trout, anchovies and sardines—is a good source and eating it once a week can make a useful contribution to vitamin D intake. Although oily fish is the richest food source, providing around 3–8 μg of vitamin D per 100 g, few people eat oily fish (Bates et al, 2012). Some types of fish, such as shark, swordfish and marlin, should be avoided during pregnancy, and intake of tuna should be limited to no more than two tuna steaks a week or four medium-size cans of tuna a week, to avoid high intakes of mercury and other contaminants (NHS Choices, 2015b). Alternative dietary sources of vitamin D include eggs (a boiled egg provides 3.2 µg) and some fortified breakfast cereals (levels can vary from 1.5–8.5 µg/100 g) (Williamson and Wyness, 2013). Spreading a slice of bread with fortified margarine or spread provides 0.6 μg, and 100 g of lean beef provides 0.7 μg of vitamin D.
Poor maternal vitamin D status will have an impact on that of the infant and his or her long-term bone health (British Nutrition Foundation, 2013). Therefore, a daily supplement of 10 μg of vitamin D is recommended for all women throughout pregnancy and breastfeeding. Low vitamin D status and a lack of awareness of the importance of a daily 10 µg supplement of vitamin D during pregnancy and breastfeeding is widespread across the UK population, particularly among young Asian and African-Caribbean women. In a study of UK pregnant women from minority ethnic groups, more than 50% had a low vitamin D status (Datta et al, 2002). A re-emergence of rickets has been seen in some population groups in the UK, predominantly in people of African-Carribean and South Asian origin (Lanham-New et al, 2011). Some women can obtain free vitamin supplements via the Government's Healthy Start scheme (Gov.uk, 2015).
Many women in the UK have low vitamin D blood levels, especially in winter and early spring. Serum/plasma 25-hydroxyvitamin D (25(OH)D) concentrations reflect the availability of vitamin D in the body from both dietary and endogenous sources (i.e. the action on sunlight on skin). A serum/plasma 25(OH)D concentration of below 25 nmol/L is currently used to indicate low vitamin D concentrations (DH, 1991). A cohort study of pregnant women in north-west London (n=346) (McAree et al, 2013) reported that the proportion with a plasma 25(OH)D concentration below 25 nmol/L was 49% in winter and 29% in summer. In a study by Haggarty et al (2013) that included pregnant women (n=1205) in Aberdeen, Scotland, the percentage with plasma 25(OH)D concentration below 25 nmol/L was 76% in winter and 25% in summer. Women with darker skin or who conceal most of their skin, or those who are housebound, are most at risk of low vitamin D status. Obese women are likely to be at increased risk of vitamin D deficiency, as pre-pregnancy weight is inversely associated with a lower serum vitamin D concentration (British Nutrition Foundation, 2013). A letter from the UK Chief Medical Officers to health professionals was issued in February 2012 to raise awareness of the risk of vitamin D deficiency among at-risk groups (Davies et al, 2012). Many women in the UK have a low vitamin D status which, if severe, puts them at risk of osteomalacia, the adult form of rickets (DH, 1991).
Vitamin A
Vitamin A is essential for normal structure and function of skin. It is also vital for vision, growth and a healthy immune system. Vitamin A can be obtained in two forms: preformed retinol found in animal-derived foods, and carotenoids, which are mainly plant-derived (beta-carotene being the most abundant carotenoid), some of which can be converted to retinol in the body. For this reason, amounts of vitamin A are measured in retinol equivalents. One retinol equivalent is equal to 1 µg of retinol, or 6 µg of beta-carotene.
The average daily intake of vitamin A among women aged 19–64 is 944 μg, with around 1 in 20 (5%) adult women having intakes below the LRNI, indicating this intake is inadequate (DH, 1991). Pregnant women require an additional 100 µg/day and breastfeeding women require an additional 350 µg/day of vitamin A (on top of the 600 μg per day required by adult women) (DH, 1991). Most pregnant women in the UK have a vitamin A intake in excess of the RNI, and therefore only a small number are likely to need supplementary vitamin A during pregnancy (DH, 1991). Large amounts of this fat-soluble vitamin can harm the unborn baby, causing malformations. Some types of animal products, such as liver, contain high levels of vitamin A and should be avoided. Intakes of retinol equivalents greater than 3000 µg/day are considered potentially dangerous in pregnancy. This level of intake is most likely to result from supplements, including the use of fish oils. For example, a cod liver oil capsule containing 1000 mg (1 g) of cod liver oil is likely to contain about 800 µg of retinol equivalents. Therefore, a teaspoon of cod liver oil (5 g) will exceed the upper recommended level of 3000 µg (Crawley, 2014).
Sources of vitamin A include cheese, butter, margarine and reduced-fat spreads, to which vitamin A is often voluntarily added (British Nutrition Foundation, 2013). Carotenoids such as beta-carotene can be converted to vitamin A in the body. Dietary sources of carotenoids include dark green leafy vegetables, orange-coloured fruits (such as mangoes and apricots) and vegetables such as sweet potatoes, carrots and tomatoes (Crawley, 2014).
B vitamins
Vitamin B2 helps to release energy from food and maintain the health of mucous membranes, such as those in the mouth and intestines. Adult women require 1.1 mg/day of vitamin B2, but pregnant women need an additional 0.3 mg/day and breastfeeding women need an extra 0.5 mg/day (DH, 1991). This extra amount of vitamin B2 can be found in a small bowl of fortified breakfast cereal. Many women get most of their vitamin B2 from animal sources, especially dairy foods such as milk, cheese and yoghurt. Around 12% of women aged 19–64 have average daily vitamin B2 intakes below the LRNI (Bates et al, 2014).
Vitamin B12 helps make red blood cells and keeps the nervous system healthy. The RNI during pregnancy remains at the same level as that for non-pregnant women (1.5 μg/day). However, breastfeeding women need an additional 0.5 μg/day of vitamin B12 (DH, 1991). Vitamin B12 is found in almost all foods of animal origin, such as meat, fish, poultry, eggs, milk and dairy products, as well as yeast extract and fortified breakfast cereals. The current average intake of vitamin B12 among adult women aged 19–64 is 4.6 μg/day (Bates et al, 2014). However, vegetarian diets that contain only small amounts of dairy products and eggs, and particularly vegan diets where no animal products are consumed, are likely to be lacking in vitamin B12 (and may be also be low in calcium, vitamin B2, iron and vitamin D) (Lennox et al, 2013). Women with vegan diets may require vitamin B12 supplementation.
Suitable vitamin supplements
A daily folic acid supplement is recommended for women before conception and during the first 12 weeks of pregnancy, and all pregnant and breastfeeding women should take a daily vitamin D supplement. Some women (all those under 18 and those who receive certain benefits) may be entitled to receive free vitamin supplements of folic acid, vitamin D and vitamin C via the Government's Healthy Start scheme (www.healthystart.nhs.uk). No other supplements are recommended, and some may even be harmful. General multivitamins that contain vitamin A (retinol) are unsuitable, as high intakes of this vitamin in supplement form can be dangerous for the fetus. Any supplements containing vitamin A, high-dose multivitamin supplements and fish liver oil supplements should be avoided. Certain herbal preparations should also be avoided as they may not be safe (Crawley, 2014). Taking many supplements does not improve health, and may have an adverse impact on health.
Vegan pregnant women may require vitamin B12 supplementation in addition to folic acid and vitamin D (Crawley, 2014). The Vegan Society produces a supplement called VEG1—which contains vitamins B2, B6 and B12, vitamin D, folic acid, iodine and selenium—specifically for vegan pregnant women (Vegan Society, 2015).
Resources
Health professionals may direct pregnant women to the pregnancy and baby guide available from the NHS Choices website (www.nhs.uk/Conditions/pregnancy-and-baby/pages/pregnancy-and-baby-care.aspx). There are also a variety of resources available from First Steps Nutrition Trust (www.firststepsnutrition.org) on topics including eating well in pregnancy and making the most of Healthy Start. To help women make positive changes to their health both before and after pregnancy, the British Nutrition Foundation has produced a 4-week planner along with information and practical advice on healthy eating and physical activity, which is free to download from its website (www.nutrition.org.uk/healthyliving).
Conclusion
A healthy, varied diet is important for ensuring both the mother and her developing baby receive adequate nutrition. This article has highlighted key vitamins that are needed during pregnancy and breastfeeding. Wherever possible, these should be provided by a good diet. However, supplements of folic acid (around early pregnancy) and vitamin D for pregnant and breastfeeding women are recommended, and vegan pregnant women may require supplementation of vitamin B12, among other nutrients. Free vitamin supplements are available to some women through the Government's Healthy Start scheme. Good nutrition and a healthy lifestyle around the time of pregnancy and breastfeeding are likely to benefit the health of both mother and baby—and, therefore, the health of future generations.
‘A healthy, varied diet is important for ensuring both the mother and her developing baby receive adequate nutrition’