Although during pregnancy a number of metabolic adaptations are orchestrated to support both increased maternal and fetal needs for many nutrients, the body's requirements for some nutrients cannot be met without increased dietary intake. Indeed, available evidence indicates that dietary requirements for 14 of the 21 essential micronutrients increase during pregnancy. These nutrients comprise seven vitamins, five minerals, and choline . As such, it is important to increase one's intake of these nutrients to prevent deficiencies. It is also important during this period of the lifespan to not consume too much of each nutrient to reduce risk for levels of intake that may be harmful.
The Institute of Medicine's (IOM) Dietary Reference Intakes (DRIs) are considered to be the gold standard in recommendations for nutrient intake, and having a basic knowledge of this set of dietary reference standards is important for understanding nutrient requirements and potential impacts of dietary supplements during pregnancy. The DRIs comprise several sets of nutrient intake standards, perhaps the most clinically important being the Recommended Dietary Allowances (RDA), the Adequate Intake Levels (AI), and the Tolerable Upper Intake Levels (UL). The RDA values represent evidence-based estimates of nutrient intakes that meet the need of approximately 97% of the population, and the AI values are derived when less solid scientific data are available. Both RDA and AI values are often used by practitioners as recommended intakes. Conversely, UL values represent the amount above which one should not consume a particular nutrient, and many of these values are based on findings of toxicity due to dietary supplement usage. As will be described throughout this chapter, dietary supplement intake should never exceed UL values. The relationships among the RDA, AI, and UL values are illustrated in Fig. 14.1.
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