PRENATAL VITAMINS

March of Dimes Updates

Are prenatal vitamins enough?

From the March of Dimes Birth Defects Foundation

Folic acid, calcium, and iron are essential not only during pregnancy but also for long-term health. But supplements may not meet all of a patient's nutritional needs.

Vitamin deficiency is a common problem even among affluent countries such as the United States—where most of the population suffers from over-nutrition—because of lifestyle issues, age, and underlying disease. For women, folic acid, calcium, and iron are especially important to good health, and daily requirements vary depending on age, pregnancy status, and lactation (Table 1). It's particularly critical that a woman's nutritional requirements be met during pregnancy, hence the common practice of prescribing prenatal vitamins. But should you rely on a prenatal vitamin to provide sufficient nutrients for your patients? Let's compare the content of a typical prenatal vitamin (Table 2) with the latest Institute of Medicine (IOM) guidelines for folic acid, calcium, and iron during pregnancy to see if your patients need something more.

TABLE 1
Dietary Reference Intakes for folic acid, calcium, and iron for females

TABLE 2
What's in prenatal supplements?

Each tablet of a commonly prescribed prenatal vitamin provides:

Vitamin A: 4,000 IU (100% as beta carotene) = 50% daily value

Vitamin C: 120 mg = 200% daily value

Vitamin D: 400 IU = 100% daily value

Vitamin E: 30 IU = 100% daily value

Vitamin B₆: 2.6 mg = 104% daily value

Vitamin B₁₂: 8 µg = 100% daily value

Thiamin: 1.8 mg = 106% daily value

Riboflavin: 1.7 mg = 85% daily value

Niacin: 20 mg = 100% daily value

Calcium: 200 mg = 15% daily value

Iron: 28 mg = 156% daily value

Zinc: 25 mg = 167% daily value

Folic Acid: 800 µg = 100% daily value

Source: From Stuart Prenatal available online at:
http://www.stuartnatal.com/healthcare_professionals/stuart_prenatal_pi.html

Dietary guidelines versus reality

The IOM recommendations for adequate daily intake of vitamins and minerals—or dietary reference intakes (DRIs)—are designed to prevent deficiencies.^1,2 Most pregnant women, says the IOM, could obtain sufficient nutrients (except iron) through diet, but few Americans have nutritionally adequate diets.^3,4 Most ob/gyns and the March of Dimes agree with the Department of Health and Human Services' 1989 recommendation that a woman's first prenatal visit occur before pregnancy.⁵ Some ob/gyns advise women who are planning a pregnancy to start taking prenatal vitamins before conception to ensure adequate levels of essential nutrients and prevent adverse pregnancy outcomes. Pre- and periconceptional folic acid is especially important for prevention of birth defects such as neural tube defects (NTDs).

Folic acid: more than preventing birth defects

In 1992, the US Public Health Service recommended that all women of childbearing age consume 400 µg of folic acid daily to prevent NTDs such as spina bifida and anencephaly. If this recommendation were followed—starting before and continuing during early pregnancy—says the Centers for Disease Control and Prevention, 50% to 70% of NTDs could be prevented.⁵ In fact, researchers have recently noted that with folic acid fortification of grain products at a level of 140 µg/100 g since 1998, there has been a 32% drop in the rate of pregnant women found at high risk of NTDs and a 20% drop in infants born with NTDs in the US.⁶

Most prenatal vitamins contain 800 to 1,000 µg of folic acid, or more than enough for embryogenesis and fetal development.⁷ But to be effective, folic acid must be ingested at least 1 month before conception and taken for at least the first 4 weeks of embryo development. It's not enough to start supplementation when a pregnancy is confirmed, because the neural tube closes by about the 28th day after conception, before many women know they are pregnant.⁵

Taking a prenatal vitamin with folic acid during pregnancy also is important for continuing fetal development. According to two recent large population studies in China and Sweden, pregnant women with low blood levels of folate are more likely to have early spontaneous abortions than those who have adequate levels.^8,9 The researchers also found that women with high levels of folate are no more likely to have early spontaneous abortions than women with moderate but adequate folate levels.⁹

The American College of Obstetricians and Gynecologists recommends that all low-risk women of childbearing age take a 400-µg folic acid supplement daily because dietary sources alone are insufficient.¹⁰ Supplementation with 4 mg (or 4,000 µg) per day is recommended for women at high risk—those who have an NTD, have had a previous NTD-affected pregnancy, or are on certain anti-seizure medications. The higher levels should be achieved by taking a separate folic acid supplement rather than more multivitamins because of the risk of vitamin A toxicity and teratogenicity.^10,11

The calcium gap

Calcium is critical for building strong, healthy bones and teeth, for normal functioning of the heart, nerves, and muscles, and to support embryogenesis and fetal development during pregnancy. Some studies also suggest that calcium can help reduce the risk of breast and colon cancer.^12,13 The Recommended Dietary Allowance for all women aged 19 to 50, including those who are pregnant and lactating, is 1,000 mg per day (Table 1).²

Calcium is particularly important during childhood and adolescence. According to a national study, 85% of females aged 12 to 19 do not consume the Recommended Daily Allowance for calcium, which is 1,300 mg (Table 3), irrespective of pregnancy status.^2,14 (For more information on childhood and adolescent calcium intake, visit the National Institute of Child Health and Human Development (NICHD) Web site at http://www.nichd.nih.gov/milk/healthresearch/fact_sheet.cfm .)

TABLE 3
Daily calcium recommendations vs. actual consumption

Most prenatal vitamins contain only 200 to 450 mg of calcium, far less than the 1,000 mg per day recommended by the IOM and ACOG for pregnant women.¹⁵ Wise dietary choices can make up the additional calcium required to prevent deficiency. Sufficient calcium can be obtained exclusively from a healthy diet that includes foods such as dairy products and leafy green vegetables, but calcium supplements also are an option (see "Calcium for life".)

Bridging the gap with calcium supplements

Calcium supplements are available in tablets, caplets, softgels, syrups, chewable tablets, antacids and calcium-fortified juices and foods. (Check the nutrition label for the level of fortification.) The most common and least expensive form is calcium carbonate.¹⁶

Patients may appreciate knowing that chewable calcium tablets and powders may be more easily absorbed than hard, compressed tablets. A "USP" on the supplement label guarantees that the tablet will dissolve after being swallowed. (More information about The United States Pharmacopeial Convention is available online at http://www.usp.org/index.html .)

Calcium supplements that may contain lead—especially those made from bone meal, dolomite, or natural oyster shell—should be avoided.¹⁷

Calcium's partner: vitamin D

The body requires vitamin D to absorb and use calcium. Adequate intake for all females aged 9 to 50, including those who are pregnant or lactating, is 5 mg/d; women older than 50 require 10 mg/d and 15 mg/d is necessary for those aged 70 and older.² Exposure to sunshine is the major source of vitamin D for many US women. A few minutes of skin exposure without sunscreen—if only of the face and hands—can provide the necessary amount.^18,19 Some prenatal vitamins contain vitamin D.

Bone loss

Maintaining adequate calcium intake when a woman is young is especially important because it can help lower the risk of bone loss and fractures associated with osteoporosis later in life (see "Calcium for life".)²⁰

Surprising iron deficiency in the US

Although iron deficiency is more common in developing countries, a significant incidence has been observed in the US since the early 1990s, among certain populations such as toddlers and females of childbearing age.²¹ The CDC says that iron deficiency affects 7.8 million adolescent girls and women of childbearing age.²¹The condition should be of concern to ob/gyns because maternal iron deficiency has been associated with low birthweight and preterm delivery.²² One of the national health objectives for 2010 is to reduce iron deficiency in these vulnerable populations (Objective No. 19-12).²³

Iron deficiency anemia (IDA) is common in pregnancy but not yet fully understood. The exact prevalence of the disorder is unknown. National data indicate that only one fourth of all females of childbearing age (12 to 49) meet the US RDA for iron (15 mg) through diet.²⁴ The IOM cites 27 mg of iron as the DRI for all pregnant women aged 18 to 50.¹ The high prevalence of IDA in pregnancy is explained by the increased demand for iron placed on a pregnant woman by the developing fetus and placenta at the same time that her red blood cell mass is expanding. In a 1990 IOM report, higher risk for IDA of pregnancy has been associated with poor socioeconomic status, low iron intake, high parity, adolescence, and regular use of aspirin.²⁴ Because IDA is alarmingly common in adolescents after menstruation begins, ACOG recommends that they increase their intake of meats, dried beans, and iron-fortified cereals. ¹⁹

Sources of iron include fruits, vegetables, fortified bread, and grain products such as cereals (all considered non-heme iron sources), and meat and poultry (heme iron sources). Because non-heme iron is more poorly absorbed than heme iron, the IOM suggests a twofold increase in iron for vegetarians.¹ Most but not all prenatal vitamins contain iron, typically at a dose of 30 to 40 mg.⁵ If a prenatal vitamin does not contain iron, prescribe an iron supplement.

Some obstacles to compliance

Prenatal vitamins can be very effective as supplements to a healthy diet during pregnancy and lactation—if your patient actually consumes her supplement as prescribed. But as many as 50% to 90% of women have difficulty with nausea during their pregnancy.²⁵ If that is the case, prenatal supplements in the form of chewable tablets, dissolvable powders, and effervescent blends may be more tolerable.

Summing up

Folic acid. Prenatal vitamins are a good source of folic acid during pregnancy. Sometimes clinicians encourage new mothers to stay on prenatal vitamins because they contain 800 µg of folic acid or more, versus only 400 µg in most regular multivitamins. Ideally, a prenatal vitamin with folic acid should be started before conception and continued through pregnancy and lactation.

Calcium. Although calcium is available from many dietary sources, particularly dairy products, most young women do not consume the 1,000 mg per day required. That deficiency can have serious long-term effects on bone health, especially after menopause. During pregnancy, prenatal vitamins (which don't contain sufficient calcium) should be supplemented with calcium from dietary sources and perhaps even an over-the-counter calcium supplement or antacid.

Iron. With many women choosing to exclude heme iron sources from their diets in favor of a vegetarian lifestyle, iron deficiency is on the rise in the US. These patients need counseling about being vigilant in consuming green, leafy vegetables and perhaps a daily iron supplement to meet their health needs, especially during the last two trimesters of gestation.

Prenatal vitamins are not enough. Ob/gyns need to counsel women of all ages, including those who are pregnant, about good nutrition and daily requirements for key nutrients. This is consistent with the Healthy People 2010 objective of increasing the proportion of people appropriately counseled about health behaviors, including nutrition.²³ Folic acid, calcium, and iron are essential during pregnancy and a typical prenatal vitamin needs to be supplemented with calcium sufficient to equal 1,000 mg/day; an iron supplement also is necessary if a woman's prenatal vitamin does not supply 27 mg/day.

The annual "well-woman" gynecologic visits conducted by ob/gyns also offer an opportunity to counsel patients on improving their nutrition. A recent survey showed that only 32% of women of childbearing age (18–45) take a multivitamin containing folic acid every day.²⁶ ACOG notes that "the obstetrician/gynecologist is in an excellent position to improve women's health through attention to nutrition."¹⁹ The survey findings underscore that fact: 89% of women polled who did not currently take vitamins or mineral supplements on a daily basis said they would be likely to do so if supplementation was advised by their physician or health-care provider.²⁶

REFERENCES

1. Institute of Medicine Dietary Reference Intakes: Elements. Available online July 29, 2003 at http://www.iom.edu/includes/DBFile.asp?id=7294 .

2. Institute of Medicine Dietary Reference Intakes: Vitamins. Available online July 29, 2003 at http://www.iom.edu/includes/DBFile.asp?id=7296 .

3. Basiotis PP, Carlson A, Gerrior SA, et al. The Healthy Eating Index: 1999-2000. U.S. Department of Agriculture, Center for Nutrition and Policy Promotion.CNPP-12. Available online November 21, 2003 at http://www.usda.gov/cnpp/Pubs/HEI/HEI99-00report.pdf .

4. Centers for Disease Control and Prevention. The burden of chronic diseases and their risk factors. National and state perspectives 2002. Section III Risk factors and use of preventive services, United States. Poor nutrition among adults. Available online November 19, 2003 at http://www.cdc.gov/nccdphp/burdenbook2002/03_nutriadult.htm .

5. Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities. Health Professional: Folic acid. Available online July 28, 2003 at http://www.cdc.gov/ncbddd/folicacid/prof.htm .

6. Evans MI, Llurba E, Landsberger EJ, et al. Impact of folic acid fortification in the United States: Markedly diminished high maternal serum alpha-fetoprotein values. Obstet Gynecol. 2004;103:474-479.

7. Physicians' Desk Reference. 57th ed. Thomson Medical Economics. Montvale, NJ. 2003.

8. Ronnenberg AG, Goldman MB, Chen D, et al. Preconception folate and vitamin B⁶ Status and clinical spontaneous abortion in Chinese women. Obstet Gynecol. 2002;100:107-113.

9. George L, Mills JL, Johansson AL, et al. Plasma folate levels and risk of spontaneous abortion. JAMA. 2002;288:1867-1873.

10. American College of Obstetricians and Gynecologists. Neural tube defects, ACOG Practice Bulletin. No. 44, July 2003. Washington, DC.

11. Rothman KJ, Moore LL, Singer MR, et al. Teratogenicity of high vitamin A intake. N Engl J Med. 1995;333:1369-1373.

12. Bonithon-Kopp C, Kronberg O, Giacosa A, et al, for the European Cancer Prevention Organization Study Group. Calcium and fibre supplementation in prevention of colorectal adenoma recurrence: a randomised intervention trial. Lancet. 2000;356:1300-1306.

13. Greenwald P, McDonald SS. Cancer prevention: the roles of diet and chemoprevention. Cancer Control. 1997;Mar 4(2):118-127.

14. National Institute for Child Health and Development. Fact sheet for professionals. Why Milk Matters: Questions and Answers for Professionals. Available online June 22, 2003 at http://www.nichd.nih.gov/milk/healthresearch/fact_sheet.cfm .

15. American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. Guidelines for Prenatal Care. 5th ed. 2002 p.81 Elk Grove Village, Illinois and Washington D.C.

16. Consumer Lab.com-Calcium review posted 6/10/03. Available online at http://www.consumerlab.com/results/calcium.asp .

17. Ross EA, Szabo NJ, Tebbett IR. Lead content in calcium supplements. JAMA. 2000;284:1425-1429.

18. Holick MF. Sunlight "D"ilemma: risk of skin cancer or bone disease and muscle weakness. Lancet. 2001;357:4-6.

19. American College of Obstetricians and Gynecologists. Nutrition and women. ACOG Educational Bulletin, Number 229, October 1996. Compendium of Selected Publications, 2001. Washington. D.C.

20. Wehren LE, Siris ES. Managing bone loss. Contemporary Ob/Gyn. 2003;(July)43:42-52.

21. Iron deficiency—United States, 1999-2000. MMWR Morb Mortal Wkly Rep. 2002;51(40);897-899.

22. Rasmussen KM. Is there a causal relationship between iron deficiency or iron-deficiency anemia and weight at birth, length of gestation and perinatal mortality? J Nutr. 2001;131:590S-603S.

23. U.S. Department of Health and Human Services. Healthy People 2010. 2nd ed. With Understanding and Improving Health and Objectives for Improving Health. 2 vols. Washington, DC: U.S. Government Printing Office; November 2000.

24. Barclay L, Vega C. Low-dose iron supplements safe, effective in pregnancy. Medscape Medical News. Available online August 27, 2003 at www.medscape.com/viewarticle/458222 .

25. von Dadelszen P. The etiology of nausea and vomiting of pregnancy. In: Koren G, Bishai R, eds. Nausea and Vomiting of Pregnancy: State of the Art. 2000, Vol 1. Transcontinental Inc. Canada.

26. March of Dimes. Folic acid and the prevention of birth defects: a national survey of pre-pregnancy awareness and behavior among women of childbearing age, 1995-2003. August 2003.

Calcium for life

Low calcium consumption and inadequate weight-bearing exercise contribute to osteoporosis, which causes 1.5 million bone fractures a year. About 10 million Americans have osteoporosis and an estimated 41 million may develop osteoporosis or low bone mass by 2015 unless steps are taken to prevent, detect, and treat the disease.

Two important factors that influence the incidence of osteoporosis are: (1) peak bone mass attained during the first two to three decades of life; and (2) the rate at which bone is lost in the later years. Childhood and adolescence are critical periods for bone development because most bone mass accumulates during this time. By the time adolescents finish their "growth spurt" around age 17, approximately 90% of their adult bone mass will have been established. Bones then continue to grow more dense until around age 30, when peak bone mass is reached. At that point, bone mass and density may remain steady, or bone loss may begin to occur at a rate of up to about 1% per year. Maintaining DRI for calcium is important through every life stage (Table 1).

Key factors affecting bone development

Q: How does bioavailability affect calcium absorption?

A: Bioavailability is the degree to which the intestinal system can absorb calcium. Absorption depends on the overall level of calcium in the food and the type of food being consumed. Foods vary in their ability to enhance or inhibit calcium absorption. The efficiency of calcium absorption is fairly similar for foods such as dairy products and grains. However, calcium may be poorly absorbed in foods high in oxalic acid (spinach, sweet potatoes, and beans) or phytic acid (unleavened bread, raw beans, seeds, and nuts). Oxalates in particular are strong inhibitors of calcium absorption. As a result, additional servings of many calcium-rich foods are needed to compensate for their low calcium absorption. According to the National Academy of Sciences report on the new DRIs, the body absorbs about one tenth as much calcium from spinach as it does from milk.

Q: What other factors can affect bone development?

A: Vitamin D - Vitamin D is an essential factor in bone mineralization, assisting in calcium absorption. It acts to increase absorption from the gastrointestinal tract by encouraging active transport of calcium through the epithelium of the ileum.¹ Deficiencies of this vitamin are responsible for serious abnormalities in the mineralization of newly formed bone and result in reduced absorption.

Physical Activity - Weight-bearing activity determines the strength, shape, and mass of bone. Activities such as running, jumping, and dancing, as well as those that increase strength, can help bone development. Studies show that absence of exercise will result in a loss of bone mass, especially during long periods of immobilization.

1. Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities. Health Professional: Folic acid. Available online July 28, 2003 at http://www.cdc.gov/ncbddd/folicacid/prof.htm .

Source: NICHD. Why Milk Matters. Questions and Answers for Professionals. Available online at http://www.nichd.nih.gov/milk/healthresearch/fact_sheet.cfm .

 

Ellen Fiore. March of Dimes: Are prenatal vitamins enough? Contemporary Ob/Gyn May 1, 2004;49:102-115.