There is a growing awareness that anaemic pregnant and lactating women in developing countries are likely to be deficient in many other micronutrients besides iron and folate. Candidate nutrients include vitamin A. zinc and the B-vitamins. These deficiencies are caused by an inadequate dietary intake, exacerbated by the nutrient demands of the rapidly growing foetus and milk production. These deficiencies lead to increased risk of maternal and child morbidity, and leaves the mother in a more severely depleted state for her next pregnancy.
A vitamin and mineral supplement is the most common prescription provided to pregnant women. Micronutrient status also plays a crucial in infant survival growth and development. It is known that the prevalence of iron deficiency anaemia, and sub -clinical vitamin A deficiency among infants is common. Similar deficiencies are also likely to exist for several other micronutrients, including zinc.
This article reviews current recommendations for nutrient supplementation in women of reproductive age.
Recommended dietary allowances
The Recommended Dietary Allowances ( RDA ) are defined to be used as reference values as goals for good nutrition. They are targeted to meet the needs of practically all health persons, and therefore, values may be higher than the amount actually required for some individuals.
Vitamin and mineral supplement selection depends on the presence of risk factors as determined by history and physical examination and laboratory data. If recommendations to improve dietary intake are judged to be unsuccessful or insufficient, then nutrient supplement may be indicated.
Micronutrient supplementation is recommended for women at risk. It should be emphasized that vitamin and mineral supplementation does not lesson the need for consumption of a nutritionally balanced diet and continued nutritional counseling.Women who are complete vegetarians or have a poor – quality diet ( and are resistant to change), heavy cigarette smokers, and alcohol and drug abusers may benefit from a low – dose multivitamin / mineral supplement. Women with multifetal gestations also have increased nutrient requirements. To promote absorption of these nutrients, the supplement should be taken between meals or at bedtime.(Nutrition during pregnancy & lactation: An Implementation Guide,1992).
Folate is a necessary co-enzyme for normal metabolism, tissue turnover, and growth. During periods of rapid growth, folate requirements are larger because of increased cell division and metabolism. During pregnancy, folate is additionally important in organogenesis. Inadequate dietary intake in the first few weeks of pregnancy is associated with an increased risk of neural tube defect. Increases in dietary folate requirements during pregnancy are related to maternal erythropoiesis, uterine and mammary tissue growth, and placental and fetal growth. Increased demand resulting in low plasma folate levels can lead to megaloblastic erythropoiesis and, rarely, megaloblastic anaemia.
There are three potential strategies for increasing folic acid intake :
- Alteration in diet,
- vitamin supplementation, or
- fortification of foods
The recommended level of folate can easily be met with supplementation.
Cyanocobalamin ( vitamin B12 ) is necessary for normal cell division & protein synthesis. It occurs naturally only in animal protein foods such as meat, fish, eggs, and milk. The level of vitamin B12 in maternal plasma decreases during pregnancy owing in part to a reduction in plasma binders. Deficiency due to dietary restrictions can be seen in long -term strict vegetarians. Vitamin B12 deficiency can become profound in breast – fed infants of vegetarian mothers. A daily vitamin B supplement of 2 mug is recommended for complete vegetarians.
Pyridoxine is required for protein, carbohydrate, and lipid metabolism, as well as erythrocyte and immune function. The need for B6 is transported across the placenta into fetal blood where concentrations are two to five times higher than in the maternal circulation.Vitamin B6 supplementation in the dose of 5 to 100 mg / day was claimed to be effective in treatment of nausea and vomiting of early pregnancy.
Vitamin C in its predominant form as ascorbic acid functions as a chemical reducing agent and is essential to a variety of the body’s metabolic processes. Vitamin C deficiency can result in impaired collagen synthesis, which ultimately leads to scurvy. During pregnancy, plasma levels of vitamin C normally fall 10% to 15% This decline is attributed to plasma volume expansion rather than increased demands of maternal or fetal tissue. Vitamin C levels in the fetus at term are generally 50% higher than in the mother It is estimated that an increase of 10 mg / day of vitamin C is required to meet the increase in maternal and fetal needs. As with most of the water – soluble vitamins, the RDA of 70 mg /day of vitamin C can be readily met by a diet that includes fruits and vegetables. A supplement of 50mg /day for women at risk of deficiency is recommended if increased consumption of fruits and vegetables is unlikely.
Vitamin A is a fat -soluble vitamin and includes a group of closed compounds with similar biologic activity. Vitamin A aids in glycoprotein synthesis and promoting cell growth and differentiation. It is also involved in photochemical reactions in the retina. Requirements do not increase substantially during pregnancy; therefore supplementation does not appear to be necessary for most women.
Iron deficiency is the most common cause of anaemia during pregnancy. There are several reasons for increased iron requirements during pregnancy. Approximately 300mg of iron is transferred to the fetus and placenta. Five hundred milligrams are incorporated into the expanding maternal hemoglobin mass. Few women have adequate iron stores to meet the increased need imposed by pregnancy. The RDA of 15 mg of dietary iron per day for non-pregnant women is doubled to 30mg during pregnancy. To prevent iron deficiency anaemia, low-dose supplementation is recommended in the second and third trimester. Thirty milligrams of elemental iron per day, alone or as part of a multivitamin mineral supplement, is recommended. Iron supplementation should not be taken with milk, tea, or coffee.
Iron-deficiency anemia is common among pregnant women. women of low socioeconomic status, low levels of education and high parity are at increased risk.
Maternal calcium requirements increase during pregnancy. Calcium – regulating hormones are altered such that there is increased calcium absorption by the intestine. The pregnant women retains about 30 g of calcium most of which is deposited in the fetus in the third trimester. Between 50 and 350 mg of ionized calcium /day is transferred to the fetus. This is an active process that occurs against a concentration gradient. The amount of calcium transferred to the fetus is only a small fraction ( 2.5 % ) of total maternal calcium stored primarily as bone. Calcium balance during pregnancy is also affected by increased urinary excretion, probably due to the higher glomerular filtration rate.
The RDA during pregnancy and lactation is 1200 mg. Certain at-risk groups may benefit from extra supplemental calcium, specifically adolescents and women who are lactose intolerant. Leg cramps in pregnant women have been attributed to alterations in calcium metabolism, but the effectiveness of treatment by supplementation is doubtful.
Vitamin D is essential to promote calcium absorption. Exposure of the skin to sunlight is a major source of vitamin D. Primary dietary source of Vitamin D for women is fortified milk.
Zinc and zinc-dependent enzymes are involved in most major metabolic pathways, and hence are essential for growth.Zinc supplementation is recommended when >30mg. per day of supplemental iron is administered to treat anaemia. Iron may interfere with absorption and use of zinc and copper. Large doses of iron appear to depress plasma zinc in pregnant women.
A multivitamin and mineral supplement is recommended during pregnancy for women who do not ordinarily consume an adequate diet and for women in high-risk categories such as multifetal gestation, heavy cigarette smokers, and alcohol and drug abusers.
There are a wide variety of multivitamin formulations available over-the-counter. Women should be cautioned to select these over-the-counter vitamin formulations carefully or not before doctor’s approval. Overdose of certain vitamins, particularly the fat-soluble vitamins, can be deleterious in pregnancy. To summarize :
- All women of childbearing age should consume at least 0.4mg of folate daily to reduce the risk of NTD.
- The majority of women do not receive enough folic from dietary sources, even with fortification of grains, and should ensure adequate intake by use of 0.4mg folate supplement.
- Women should be educated about the potential for prevention of birth defects through adequate nutrition.
- Assessment of dietary practices is recommended for all pregnant women to evaluate need for improved diet or vitamin and mineral supplement.
- An iron supplement of 30mg ferrous iron (150mg ferrous sulfate ) is recommended in the second and third trimesters.
- A multivitamin and mineral supplement is recommended during pregnancy for women who do not ordinarily consume an adequate diet and for women in high -risk categories such as multifetal gestation, heavy cigarette smokers, and alcohol and drug abusers.