EXPANSION OF THE
DIETARY REFERENCE INTAKE MODEL

Learning from Sodium and Potassium

Good nutrition is more than just preventing deficiencies and avoiding possible adverse effects from excessive intakes—good nutrition supports health. Knowing how much of a nutrient is needed, how those needs vary within and among different groups of people, and whether there may be risks from consuming too much or too little is critical information for nutrition programs, policies, planning, assessment, and regulatory initiatives. In the United States and Canada, estimates of these intake levels are established as Dietary Reference Intakes (DRIs).


Background on the DRIs


The Food and Nutrition Board of the National Academies of Sciences, Engineering, and Medicine has published standards for nutrient intakes since the 1940s. The standards began as a single category of intake levels estimated to meet the needs of nearly all healthy persons by age and sex. By the 1990s, the nutrition research landscape had dramatically changed. A new paradigm for establishing reference nutrient intakes was needed. What emerged were the DRIs. Drawing on advancements of scientific and statistical understandings, the DRIs featured four categories of reference intake values and are intended to help individuals optimize their health, prevent disease, and avoid consuming too much of a nutrient.

DRI CATEGORIES

Estimate Average Requirement (EAR)
Average daily nutrient intake level estimated to meet the requirement of half the healthy individuals in a particular age, sex, and life-stage group

Recommended Dietary Allowance (RDA)
Average daily nutrient intake level sufficient to meet the nutrient requirement of nearly all (97-98%) healthy individuals in a particular age, sex, and life-stage group

Adequate Intake (AI)
An intake (not a requirement) that is likely to exceed the actual requirements of almost all individuals in an age, sex, and life-stage group; established when scientific evidence is not sufficient to determine an RDA

Tolerable Upper Intake Level (UL)
The highest average daily nutrient intake level likely to pose no risk of adverse health effects for nearly all people in a particular age, sex, and life-stage group

Expansion to Include a New DRI Category



Although evidence on relationships between nutrient intakes and chronic disease risk had been included in DRI reviews for various nutrients, it was often difficult to use. Some of the challenges include:

  • Chronic diseases are complex, and nutrient intake may be one of many risk factors
  • Chronic disease risk varies from person-to-person
  • Available scientific evidence often comes from studies from which it’s hard to establish cause-and-effect relationships

To overcome these limitations, a new approach for using this type of evidence in the DRI process was developed. The evidence can now be used to establish a new DRI category called the Chronic Disease Risk Reduction Intake (CDRR).

What should you know about the Chronic Disease Risk Reduction Intake (CDRR)?

  • Characterizes nutrient intakes that are expected to reduce the risk of developing chronic disease
  • Does not replace the existing DRI categories, but changes how evidence on chronic disease risk is assessed and used in the DRI process
  • Is established using a specific methodology for evaluating the strength of the body of scientific evidence
  • Is intended to be set when there is at least moderate strength of evidence for both a causal and an intake-response relationship between nutrient intake and chronic disease risk

Learning from the Update of the Sodium and Potassium DRIs


Sodium and potassium are the first two nutrients reviewed under the expanded DRI model. This 2019 review updated the sodium and potassium DRI values published in 2005 under the original DRI model. Although each nutrient has unique considerations, changes reflected in the updated sodium and potassium DRI values serve as important illustrative examples of the evolving DRI model.

Sodium

How did the expanded DRI model affect the sodium Adequate Intakes (AIs)?

There is not yet enough evidence to determine when sodium needs are met using the criteria of the DRI model. More evidence on sodium requirements of healthy people is needed. The updated values remain AIs. An AI intake level is considered to be adequate for almost all people, but its exact relationship with actual requirements is unknown.

Key Points

  • The expanded DRI model did not substantially change the approach to establishing the sodium AIs.
  • The updated sodium AIs were set based on sodium intakes that appear to be adequate using data from randomized trials and a balance study.
  • Evidence on the potential harms of low sodium intakes, including associations with cardiovascular disease and mortality, was too limited and inconsistent to be used to inform the sodium AIs.

How did the expanded DRI model affect the sodium Tolerable Upper Intake Level (UL)?

In the expanded DRI model, it’s recommended that ULs be based on adverse effects of excessive intakes that are not related to chronic disease risk, as those types of relationships are intended to be captured in the new DRI category, the CDRR. Although some studies reported non-chronic disease-related symptoms with higher or more concentrated sodium intakes, the evidence was too limited to establish a sodium UL based on this type of adverse effect.

Key Points

  • The expanded DRI model changed the approach to establishing the sodium ULs.
  • Evidence reviewed to update the sodium ULs only focused on adverse effects of excessive sodium intake that were not related to chronic disease risk.
  • Evidence of the relationship between sodium intake and blood pressure that informed the 2005 sodium ULs was now used as part of the evidence base to inform the sodium Chronic Disease Risk Reduction Intake (CDRR).

What is the sodium Chronic Disease Risk Reduction Intake (CDRR)?

Across the body of scientific studies, there was moderate strength of evidence that decreasing high sodium intakes reduces risk of cardiovascular disease and hypertension, and high strength of evidence that it lowers blood pressure. The sodium CDRR for adults was established as the lowest level of sodium intake for which there was moderate strength of evidence of chronic disease risk reduction.

Key Points

  • In the apparently healthy population, any reduction in sodium intake in the range of intakes greater than the CDRR is expected to reduce risk of cardiovascular disease and hypertension.
  • Although there is evidence that further reductions in sodium intake below the sodium CDRR may lower blood pressure, more evidence is needed to determine the effect on chronic disease risk.

Potassium

How did the expanded DRI model affect the potassium Adequate Intakes (AIs)?

There is not yet enough evidence to determine when potassium needs are met using the criteria of the DRI model. More evidence on potassium requirements of apparently healthy people is needed. The updated values remain AIs, although they are based on a different collection of evidence than the potassium AIs established in 2005. An AI intake level is considered to be adequate for almost all people, but its exact relationship with actual requirements is unknown.

Key Points

  • Evidence on potassium’s relationship with chronic disease risk, which was used to support the 2005 potassium AIs, was now reviewed to determine whether a potassium CDRR should be established.
  • Other benchmarks of adequacy not related to chronic disease risk were evaluated, but there was insufficient evidence for their use to develop potassium AIs.
  • Because the 2019 potassium AIs are now based on median intakes from national surveys, rather than on experimental studies, they are lower than the 2005 potassium AIs for all age, sex, and life-stage groups except for infants.

How did the expanded DRI model affect the potassium Tolerable Upper Intake Level (UL)?

Evidence was reviewed to find a measure, marker, or outcome that reflected potassium adverse effects or toxicity, separate from chronic disease, to establish a UL. No such indicator could be identified. As was the case in the 2005 report, potassium still does not have a UL. The lack of a potassium UL doesn’t mean that there is no risk from excessive intake. Caution against high intake through supplemental potassium is warranted for certain population groups, particularly those with or at high risk for compromised kidney function.

Key Points

  • The expanded DRI model did not substantially change the approach to establishing the potassium ULs.
  • Evidence reviewed to update the potassium ULs only focused on adverse effects of excessive potassium intake that were not related to chronic disease risk.

Why isn’t there a potassium Chronic Disease Risk Reduction Intake (CDRR)?

There’s evidence that potassium supplementation reduces blood pressure, particularly in adults with hypertension. However, across the studies, higher potassium intakes didn’t result in greater reductions in blood pressure—that is, an intake-response relationship could not be established. Evidence relating potassium intake to risk of chronic diseases, such as cardiovascular disease, was also limited. The evidence is not yet sufficient to establish a potassium CDRR. This doesn’t mean that increasing potassium intake may not reduce chronic disease risk. Rather, more evidence is needed in order to be able to characterize how chronic disease risk changes over a range of potassium intakes.

Key Points

  • Although there is evidence of blood pressure reductions in potassium supplementation trials, across studies, higher potassium intakes did not lead to greater blood pressure reductions.
  • Using the new methodologies of the expanded DRI model, a potassium CDRR was not established because the evidence for both a causal and an intake-response relationship is not yet of sufficient strength.