Dietary Reference Intakes
For Water, Potassium, Sodium, Chloride, and Sulfate
Institute of Medicine
February 11, 2004
John W. Erdman,
Nutrition Research Chair and Professor at the University of Illinois, Champaign-Urbana
Chair, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes
Professor of Medicine, Epidemiology, and International Health, Johns Hopkins
Medical Institutions, Baltimore, Md.
Chair, Panel on Dietary Reference Intakes for Electrolytes and Water
Dr. Erdman: Good morning. On behalf of the National Academies, I would like to welcome those of you in the room as well as those listening on the Web. Thank you for joining me and the chair and a member of the panel to release a report that we hope will guide policy-makers, health professionals, and others as they grapple with complex nutritional issues. The report we are releasing today is the latest in a series on nutritional reference values developed jointly by American and Canadian scientists, and it focuses on water, potassium, sodium, chloride, and sulfate.
Since 1941, the Food and Nutrition Board of the National Academies has set Recommended Dietary Allowances on the types and quantities of nutrients that are needed for healthy diets. As a result of the increasing evidence linking dietary patterns and nutrients to chronic diseases, increased emphasis is now being placed on the role of specific nutrients in the development of chronic disease. In recognition of this, 10 years ago the board implemented an expanded system for determining RDAs and other nutrient-based reference values now called Dietary Reference Intakes, or DRIs. A basic premise of the DRIs has been the review of nutrients for their role in the development of chronic diseases in addition to nutritional deficiencies. Using a model of risk assessment not unlike that applied to environmental hazards, the panel also evaluated the extent to which consuming too much of a nutrient may not be tolerated well biologically, potentially leading to health problems.
Although there are still unanswered questions about the links between electrolytes and development of chronic diseases, much is understood. Our report's findings and recommendations are based on a comprehensive review of the scientific literature in this area. The panel reviewed hundreds of studies, determined where the data are in conflict and why, and based its conclusions and recommendations on the most scientifically compelling evidence. We hope that the report brings some science-based clarity to the very complicated and often confusing debate over the role of sodium and potassium in cardiovascular disease, as well as how much water people need daily and the extent to which water deficits may exist in the generally healthy population.
So, how much of these critically essential nutrients does one need to consume on a daily basis to ensure good health? To answer that question, the panel has offered specific values called 'Adequate Intakes' for water, sodium, chloride, and potassium. Given the variability in the population, it may well be that many in the group to which the Adequate Intake for each nutrient applies will have their needs met at lower levels of intake. The Adequate Intakes – or AIs -- are reference values used when one has insufficient knowledge about a specific individual's needs. AIs therefore can be a starting point for developing an individual's diet. It must be emphasized that the Dietary Reference Intakes are not developed in isolation from the need for other important nutrients. The ability to obtain other essential nutrients at their recommended intake levels must be carefully considered when developing the AIs in order to achieve a nutritionally adequate diet while minimizing the risk for developing chronic disease.
Dr. Lawrence Appel, chair of the panel on electrolytes and water, will now review the major findings included in the report.
Dr. Appel: Thank you. I too want to welcome you to this public briefing. Let me first extend a special note of appreciation to our panel members and to the IOM staff for their commitment to this important task. Our panel deliberated for nearly two years. We listened to expert presentations, reviewed hundreds of scientific articles, and then synthesized the evidence in this report. I will briefly review our main recommendations and then we will take questions.
Sodium and potassium, together with chloride and other anions, to play essential roles in maintaining normal cell function. They do this in the water-based environment of the body.
People need certain amounts of each electrolyte for good health, but evidence suggests that too much or too little can be associated with health problems, including chronic disease. We recommend an Adequate Intake of 1.5 grams of sodium per day for adults age 19 to 50. There are populations in the world that are able to subsist on much lower sodium intakes in the range of 0.2 grams per day. Still, we are recommending that adults consume 1.5 grams of sodium per day to ensure that they have adequate amounts of sodium in the event of high sweat losses and to ensure a nutritionally adequate diet from the typical food supply available in the United States and Canada. In other words, if people choose foods that meet this level of sodium intake, they should be able to meet the recommended intakes for other nutrients such as calcium and vitamin A as well.
A substantial and growing body of evidence indicates that eating excessive amounts of sodium -- usually in the form of salt in processed foods or added by consumers -- can lead to health problems. Specifically, as sodium intake rises, so does blood pressure. Higher blood pressure increases the risk of stroke, heart disease, and kidney disease. To reduce the risk of chronic illness, we recommend that adults age 19 to 50 limit their daily intake of sodium to less than 2.3 grams.
We recognize that few Canadians and fewer Americans currently consume less than the upper level of 2.3 grams of sodium, largely because of the amounts of sodium added during food processing. Let me provide an example. Two slices of pizza contain about half of the upper level of sodium. Consuming this one meal would leave little room for additional sodium intake at other meals throughout the day. Hence, we recommend that additional research be performed to guide the food industry in developing alternative technologies to decrease the sodium content of prepared and processed foods while maintaining quality, acceptability, and cost.
Years ago, pregnant women were advised to markedly reduce their sodium intake in order to avoid pre-eclampsia, a serious problem associated with swelling and elevated blood pressure. However, studies have shown that lowering sodium intake to levels close to or below the Adequate Intake of 1.5 grams per day has no effect on whether or not this problem occurs. Thus the recommended intake for sodium during pregnancy is the same as for nonpregnant women.
The health effects of potassium have not received much attention, but one of our more interesting findings is that diets rich in potassium not only reduce blood pressure, but also blunt some of the rise in blood pressure that occurs in response to sodium intake. High intakes of potassium also reduce bone loss and can prevent kidney stone recurrence in men and women. We recommend that adults consume a diet that provides an Adequate Intake level of 4.7 grams of potassium per day, and that intake be in the form of naturally occurring potassium from fruits, vegetables, and juices.
No upper limit was established for potassium from foods. It should be noted that an increasing number of individuals in the United States and Canada need to carefully control their potassium intake -- those individuals with known kidney problems and those who are on certain diuretics, such as, spironolactone, or other blood pressure medications, such as ACE inhibitors. In these individuals, the AI level of 4.7 grams may be too high, and they should follow the advice of their health care professionals.
Turning to water, thirst provides the body feedback that we are getting dehydrated, so that we can consume more fluids. Thirst, together with typical fluid and food consumption behavior, is an effective mechanism to prevent dehydration. Thus, it is extremely unusual for healthy individuals with ready access to food and fluids to become chronically dehydrated.
Therefore, we set Adequate Intakes for total water based on the average water consumption of individuals shown to be adequately hydrated. In the United States, women who are adequately hydrated consume 2.7 liters (approximately 91 ounces) of total water from all beverages and foods, while men consume 3.7 liters (approximately 125 ounces) from all sources.
Typically, approximately 80 percent of total water comes from beverages, including drinking water, while the remaining 20 percent comes from moisture found in foods. All sources of water -- foods, drinking water, and other beverages -- can contribute to meeting water requirements. We do not offer a rule of thumb based on how many glasses of water people should drink each day because people can get their total water needs from a variety of beverages other than drinking water and from foods as well.
By consuming fluids at meals and drinking beverages between meals when thirst dictates, healthy individuals adequately satisfy their hydration needs. People who engage in strenuous or prolonged physical activity or those who are exposed to hot temperatures may need to consume more total water to replace that lost in sweat.
An important issue is whether the elderly get enough water by following their thirst. With aging, thirst declines, as does the ability of the kidneys to concentrate urine and thus conserve water decline. However, the elderly appear to adequately maintain total body water content from day to day by consuming beverages at meals and drinking fluids when thirsty. If the elderly consume total water at the Adequate Intake levels we have set, they should be adequately hydrated.
I have given the dietary reference values for adults throughout this statement. For children, the Adequate Intake levels for sodium and potassium are based on adult values and decrease proportionately based on estimated energy intake. The levels for water are based on average total water consumption by children who are adequately hydrated.
We also examined the health effects of sulfate, an inorganic ion that is routinely added to animal feed to ensure normal growth, and which humans obtain from all foods. In our evaluation of sulfate needs of humans, we determined that if individuals consumed the recommended intakes of the sulfur amino acids, which are methionine and cysteine, they would get adequate dietary amounts of sulfate as a by-product of the metabolism of the sulfur amino acids and from that naturally present in diets. Thus no recommended intakes for sulfate were set. The recommended intakes for methionine and cysteine were published in a previous report on protein needs in the Dietary Reference Intakes series.
On a final note, the panel recognizes that there have been debates on the health effects of water, sodium, potassium, and sulfate intake. There are also gaps in the available research. Hence, although our primary focus was to compile the available evidence, we also made research recommendations to guide future deliberations. I won't go through these recommendations here, but they are discussed in final chapter of the report.
This concludes my opening remarks. Dr. Erdman.
Dr. Erdman: Thank you. My colleagues and I will now take your questions. Those of you listening to our webcast can send in questions by e-mail, using a link on the National Academies home page. We ask those of you in the room to step to a microphone and identify yourself and your organization before asking your question. We'll begin with a question in the room. As there are several members of the media here today – and I know that reporters have deadlines to meet – let's start with any questions from reporters.