Calcium and Related Nutrients

 

Calcium and Related Nutrients

 

August 30, 1997

 

The Institute of Medicine (IOM) established a 9-member panel under its Food and Nutrition Board (FNB)'s Standing Committee on the Scientific Evaluation of Dietary Reference Intakes to review the scientific literature on calcium, phosphorus, magnesium, vitamin D, and fluoride metabolism in humans throughout the life span, and data on intakes in the U.S. population. Such analysis included a review of the metabolism of related nutrients and of non-nutrients, such as phytosterols and fiber, as they relate to bioavailability.

The review panel released its report on August 13, 1997. This report is the first in a series designed to be the new framework for providing guidance to federal agencies about nutrient needs and thus replace the former Recommended Dietary Allowances of the Food and Nutrition Board. The report analyzes the scientific literature regarding human requirements for calcium, phosphorus, magnesium, vitamin D and fluoride throughout the lifespan, including the relationship to chronic diseases and data on dietary intake. Where the scientific evidence is sufficient, the report recommends for each nutrient: (1) the recommended dietary allowance, which meets the needs of almost all individuals in the group and is based on estimates of average requirement; (2) an adequate intake, which is expected to meet the needs of almost all individuals in a group but for which estimates of average requirements are not available; and (3) the tolerable upper intake level, which is the maximum intake that is unlikely to pose risks of adverse health effects in almost all individuals in the group.

According to a press release issued by the Food and Nutrition Board on August 13, the report notes that people need more calcium and magnesium than indicated by the former RDA. The report is aimed at decreasing the risk of chronic disease through nutrition and recommends that Americans and Canadians at risk of osteoporosis should consume between 1,000 and 1,300 milligrams of calcium per day. This report is the first in a series of reports on Dietary Reference Intakes (DRIs) -- which will update and expand the Recommended Dietary Allowances (RDAs) set by the National Academy of Sciences since 1941. This first report focuses on calcium, phosphorus, magnesium, vitamin D and fluoride which are related to the health of bones and to other body functions. The report recommends intake levels for U.S. and Canadian individuals and population groups, and for the first time, sets maximum-level guidelines to reduce the risk of adverse health effects from overconsumption of a nutrient.

"Our understanding of the relationship between nutrition and chronic disease has progressed to the point where we can now begin to recommend intakes that are thought to help people achieve measurable physical indicators of good health," said Vernon Young, chair of the IOM's Standing Committee on Dietary Reference Intakes and professor of nutritional biochemistry, Massachusetts Institute of Technology, Cambridge. "The new DRIs represent a major leap forward in nutrition science -- from a primary concern for the prevention of deficiency to an emphasis on beneficial effects of healthy eating."

Unlike the RDAs, which established the minimal amounts of nutrients needed to be protective against possible nutrient deficiency, the new values are designed to reflect the latest understanding about nutrient requirements based on optimizing health in individuals and groups. The new recommendations, which include four categories of reference intakes, were made by a group of more than 30 U.S. and Canadian scientists who examined the results of hundreds of nutritional studies on both the beneficial aspects of nutrients and the hazards of taking too much of a nutrient. Where the scientific evidence allowed, the committee made recommendations aimed at helping individuals at different stages of life obtain enough of a nutrient to promote bone strength and to maintain normal nutritional status. Six additional reports -- on folate and B vitamins, antioxidants, macronutrients, trace elements, electrolytes and water, and other food components -- will follow.

Calcium recommendations were set at levels associated with maximum retention of body calcium, since bones that are calcium-rich are known to be less susceptible to fractures. In addition to calcium consumption, other factors that are thought to affect bone retention of calcium and risk of osteoporosis include high rates of growth in children during specific periods, hormonal status, exercise, genetics, and other diet components.

Phosphorus, an important nutrient for bone and soft tissue growth, is so prevalent in various foods that near starvation or a metabolic disorder is required to produce deficiency. Different from former RDAs, phosphorus values in the report are not derived in relation to calcium. The values recommended are considered sufficient to support normal bone growth and metabolism at various ages.

Magnesium works with many enzymes to regulate body temperature, to allow nerves and muscles to contract, and to synthesize proteins. Although some researchers have argued that magnesium recommendations should be based on relationships with the risk of cardiovascular disease, the report does not find enough data available at this time to do so. The levels recommended, although somewhat higher, do not differ substantially from the most recent RDAs but are higher than current Canadian recommendations.

Vitamin D used by the body comes mostly through exposure to the sun. Vitamin D deficiency can exacerbate osteoporosis and other bone problems in adults. The levels recommended in the report -- which are greater than those recommended in previous RDAs for people over the age of 50 -- are estimated to provide enough vitamin D even for individuals with limited sun exposure. Dietary intake of vitamin D is unnecessary for individuals who spend adequate amounts of time in the sun.

The greatest disparity between recommended values and current dietary patterns is in calcium, which in American and Canadian diets comes primarily from dairy products. Data from surveys indicate that many do not consume the amount of calcium recommended in the report. While many may be consuming sufficient intakes to meet their requirements, the recommendations are intended to provide general guidance to vulnerable individuals and population groups in order to reduce the likelihood that they will develop osteoporosis.

Although the report does not prescribe a means for increasing individual consumption of calcium, it suggests that possible methods for doing so include educating consumers to eat more calcium-rich foods, fortifying foods, and recommending dietary supplements. Individuals who wish to increase their calcium can consume more low- or non-fat dairy products, or fortified food products. According to the report, taking supplements such as calcium tablets may be appropriate for those at high risk of health problems due to low calcium intake.

Dietary Reference Intakes include:

  • Recommended Dietary Allowance: The intake that meets the nutrient need of almost all of the healthy individuals in a specific age and gender group. The RDA should be used in guiding individuals to achieve adequate nutrient intake aimed at decreasing the risk of chronic disease. It is based on estimating an average requirement plus an increase to account for the variation within a particular group. The amount of scientific evidence available allowed the committee to calculate RDAs for phosphorus and magnesium.
  • Adequate Intake: When sufficient scientific evidence is not available to estimate an average requirement, Adequate Intakes (AIs) have been set. Individuals should use the AI as a goal for intake where no RDAs exist. The AI is derived though experimental or observational data that show a mean intake which appears to sustain a desired indicator of health, such as calcium retention in bone for most members of a population group. For example, AIs have been set for infants through one year of age using the average observed nutrient intake of populations of breast-fed infants as the standard. The committee set AIs for calcium, vitamin D and fluoride
  • Estimated Average Requirement: The intake that meets the estimated nutrient need of half the individuals in a specific group. This figure is to be used as the basis for developing the RDA and is to be used by nutrition policy-makers in the evaluation of the adequacy of nutrient intakes of the group and for planning how much the group should consume.
  • Tolerable Upper Intake Level: The maximum intake by an individual that is unlikely to pose risks of adverse health effects in almost all healthy individuals in a specified group. This figure is not intended to be a recommended level of intake, and there is no established benefit for individuals to consume nutrients at levels above the RDA or AI. For most nutrients, this figure refers to total intakes from food, fortified food, and nutrient supplements.

The Institute of Medicine is a private, non-profit organization that provides health policy advice under a congressional charter granted to the National Academy of Sciences. This study was funded by the Food and Drug Administration, the U.S. Department of Agriculture, Health Canada, and the U.S. National Institutes of Health.