By Mike Murray, RDN, CSCS, CISSN
Micronutrients are essential nutrients needed by the body in very small amounts. They are intimately involved in virtually all metabolic processes and support the maintenance of tissue function.
Furthermore, failure to consume micronutrients in adequate amounts is associated with adverse health outcomes such as general fatigue, poor bone health, reduced ability to fight infections, impaired cognition, and increased risk of chronic diseases.
Micronutrients can be broadly broken down into vitamins and minerals. Vitamins are organic molecules (i.e., carbon-containing compounds) and classified as either water-soluble or fat-soluble. Minerals are inorganic substances and classified as either macrominerals or trace minerals.
The chemical structure of vitamins is similar to macronutrients (i.e., carbohydrates, fats, and protein) in that they are all organic molecules; carbohydrates and fats are made up of carbon, hydrogen, and oxygen, and proteins are polymers of amino acids, which include the former plus nitrogen. However, a fundamental difference between micronutrients and macronutrients is that micronutrients do not provide energy. Instead, they facilitate energy metabolism through their role as cofactors and coenzymes.
Water-soluble vitamins include vitamins B1 (thiamin), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin or vitamin H), B9 (folate), B12 (cobalamin), and C. Also worth mentioning, choline is a vitamin-like essential nutrient that is closely associated with the B-vitamin family. Fat-soluble vitamins include vitamins A, D, E, and K.
Water-soluble vitamins need to be replaced regularly, and excess amounts are easily excreted in the urine. In contrast, fat-soluble vitamins are stored in the body’s fatty tissue and liver, which increases the risk of toxicity if consumed in excess.
Macrominerals are required in amounts greater than 100 mg per day and include calcium, chloride, magnesium, phosphorus, potassium, and sodium. Trace minerals, on the other hand, are required in amounts less than 100 mg per day and include chromium, copper, fluoride, iodine, iron, manganese, molybdenum, selenium, and zinc.
To ensure good health across the lifespan, it’s vital to regularly consume a sufficient amount of each micronutrient. The question is, how much of each do you need?
History of the DRIs
The Recommended Dietary Allowances (RDAs) were established in 1941. They were developed to serve as a basis for food relief efforts, both in the United States and internationally, where war or economic depression had resulted in malnutrition or starvation.
Generally, the RDAs acted as a guide for adequate nutrition and a “yardstick” to measure progress towards that goal. They initially provided targets for protein, energy, and eight vitamins and minerals, and expanded over time. By 1989, the RDAs featured 25 vitamins and minerals.
Despite widening the scope of their guidance as the nutrition research evolved, major limitations remained with the RDAs. The most notable of which was a single reference value per nutrient.
With this constraint, inadequate and excessive nutrient intakes could not be determined, only the point at which intake is likely to be adequate. Additionally, it suggested that nutrient needs did not differ between sexes or change over the lifespan.
These gaps led to growing misuse of the RDAs in ways that were not scientifically validated, which further called attention to the need for the RDAs to be restructured.
The Dietary Reference Intakes (DRIs) were conceptualized in 1994, and the first reports were issued from 1997–2004. They consist of four reference values, which vary by sex and age: Recommended Dietary Allowance (RDA), Adequate Intake (AI), Tolerable Upper Intake (UL), and Estimated Average Requirement (EAR).
- RDA: The average daily nutrient intake level sufficient to meet the nutrient requirement of nearly all (97–98%) healthy individuals in a particular life stage and sex group.
- AI: A recommended average daily nutrient intake level based on observed or experimentally determined estimates of nutrient intake by apparently healthy people –– used when an RDA cannot be determined.
- UL: The highest average daily nutrient intake level likely to pose no risk of adverse health effects to almost all people.
- The potential risk of adverse health effects increases as intake increases above the UL.
- EAR: The average daily nutrient intake level estimated to meet the requirement of half the healthy individuals in a particular life stage and sex group.
- A nutrient intake below the EAR is defined as “inadequacy”.
Since their creation, the DRIs have had a substantial impact on national nutrition policy. They are used to assess national nutritional health, plan menus and meals for the military, ensure nutrient needs are met in institutional settings (e.g., long-term care facilities), guide federal nutrition assistance programs and food fortification, and serve as the basis for food labeling information.
This brings us to the central shortcoming of the DRIs: They were created in the context of public health.
The DRIs are designed to meet the needs of the average healthy person, prevent nutrient deficiencies, and avoid adverse effects of excessive intakes. They do not indicate the optimal quantity of micronutrients for a specific outcome, nor do they consider the potentially unique needs of the individual.
Limitations of the DRIs
In 1972, Herbert described the five possible causes of nutrient deficiencies: insufficient intake, impaired absorption, inadequate utilization, augmented requirement, and increased excretion. The DRIs only address one of these –– insufficient intake.
Moreover, each of these potential causes has “modifiers” that can increase the risk of deficiency or inadequacy, such as sex, pregnancy, lactation, age, disease, the microbiome, toxins, pharmaceuticals, nutrient interactions, food matrix, physical activity, genetics, and epigenetics. The DRIs consider less than half of these –– sex, age, pregnancy, and lactation.
With these points in mind, it should be clear that there are a number of potential scenarios where the DRIs may fall short. Let’s take a look at some examples.
Examples of When the DRIs May Be Insufficient
The most striking and numerous examples of when micronutrient needs will vary from the DRIs relate to clinical conditions. It is known that chronic diseases and their treatments can alter nutritional status indicators, which suggests that deviation from the DRIs is warranted to meet nutrient needs.
- Individuals with cystic fibrosis have an increased risk of fat-soluble vitamin deficiency due to pancreatic insufficiency and malabsorption.
- Vitamin D deficiency is more prevalent in individuals with obesity, which may be due to decreased bioavailability.
- Iron deficiency is prevalent in individuals with Crohn’s disease largely due to blood loss and decreased absorption.
- Metformin induces malabsorption of vitamin B12, which increases the risk of deficiency.
- Loop diuretic therapy (e.g., furosemide) increases urinary excretion of vitamin B1, which increases the risk of deficiency.
Other evidence demonstrates that micronutrient status, and the response to supplementation, is influenced by genetics. These differences insinuate that the amount of a micronutrient required to achieve optimal levels can significantly vary between individuals.
- The MTHFR TT genotype is associated with increased plasma homocysteine (a marker of folate deficiency), lowered serum folate levels, and a dampened response to folate supplementation.
- Vitamin D inadequacy has been linked to single nucleotide polymorphisms in multiple genes such as GC and DHCR7/NADSYN1, and other evidence reports that certain genetic variants can affect the response to vitamin D supplementation.
- Mutations in the TMPRSS6 gene have been associated with iron deficiency.
There are also many dietary factors that affect the bioavailability (i.e., the proportion of the ingested nutrient that is absorbed and utilized) of a nutrient. As a consequence, certain dietary patterns can alter the requirements for some micronutrients. Some examples of this relate to iron, phytate, and oxalate content in food.
- Heme iron from animal sources is more readily absorbed than iron from plant sources.
- Phytate and soybean protein reduces zinc and iron absorption.
- Oxalate reduces calcium absorption.
Lastly, high levels of intense physical activity can increase the requirement for certain micronutrients (i.e., electrolytes) due to excessive losses in sweat. The main electrolyte lost in sweat is sodium. Consider two examples in athletic populations:
- The average American football player loses ~1285 mg of sodium per hour of training or competition.
- The average endurance runner loses ~1189 mg of sodium per hour of training or competition.
The DRIs are a set of four reference values used to plan and assess nutrient intakes of healthy people. They provide guidance on how much of a micronutrient is sufficient to maintain good health, as well as intake levels that are likely inadequate and excessive.
Simply stated, the DRIs are appropriate to meet the micronutrient needs of most people most of the time.
However, they do not indicate the amount of a micronutrient that you need for your goals. As evidenced by the above, there are countless scenarios where it may be advised to diverge from the DRIs.
In future installments of this series, we will dig deeper into the aforementioned topics for each micronutrient. We will cover information such as the properties and functions of each micronutrient, nutrient requirements, factors that alter nutrient requirements, signs and symptoms of deficiency, dietary sources, and more.