Are Current Calcium Recommendations for Adolescents Higher than Needed to Achieve Optimal Peak Bone Mass? The Controversy

Abstract

Introduction The current dietary reference intakes (DRI) for calcium for North America were set by the Food and Nutrition Board a decade ago. As pediatric calcium researchers, we considered the need for revising the recommended intakes for calcium in children in light of issues and evidence that have emerged since the mid-1990s. We approached the question of whether or not calcium requirements are unnecessarily high in the form of a debate. In this commentary, our goal is not to systematically review the evidence base for considering revision of calcium intakes, but rather to discuss the pros and cons of changing calcium requirements for building peak bone mass in light of recent evidence. A particular emphasis is given to statistical issues that arise in long-term intervention studies and how these issues influence the impact of the findings. Current calcium intake recommendations for North America were published by the Institute of Medicine in 1997 (1). The panel considered calcium recommendations from several points of view, including published randomized, controlled trials (RCT), applying the factorial approach that accounted for daily calcium losses plus growth needs, adjusted for fractional calcium absorption, and the intake to achieve maximal calcium retention. The latter approach was prioritized because reports of calcium retention over a range of calcium intakes were available in adolescents, whereas dose-response RCT with bone outcome measures were not. The intake for maximal calcium retention was determined to be 1300 mg/d, using a nonlinear regression model (2), which became the adequate intake (AI) for ages 9–18 y for North America (1). Calcium retention largely reflects bone mass, because 99% of the body’s calcium is in the skeleton and exists as a constant percentage of bone mineral. Bone mass is an important component of bone strength (3). Thus, the panel reasoned that achieving maximal calcium retention would remove dietary calcium as a limiting factor for maximizing peak bone mass within one’s genetic potential to offer the greatest protection against fracture later in life. Because the DRI for calcium for adolescents was set as an AI and not an estimated average requirement (EAR) with a derived recommended dietary allowance (RDA), this value should be flagged for reconsideration. The criteria for triggers to stimulate a revision of DRI values were outlined as follows at an Institute of Medicine workshop (4): presence of an AI value, that the nutrient for the age group was identified as a research priority, that substantive new research has emerged, or that the nutrient for the age group would affect important public health policy. For the DRI value for calcium for adolescents, all of these criteria apply. The key considerations for setting recommended intakes for any nutrient are the choice of indicator of nutritional adequacy and the strength of the evidence for that chosen indicator. For calcium recommendations for adolescents, the quality of the evidence should be assessed on the following criteria: availability of dose response data, that a period of adaptation to different intakes of calcium has been included in the study design, that response has been measured for both dietary sources of calcium and calcium supplements, and that data from more than 1 laboratory are available, with adequate representation of males and females and ethnic groups. The debate outlined in this article addresses whether or not sufficient new evidence exists to revise the calcium recommendations for adolescents for North America. The debate is broadly relevant beyond North America because average calcium intakes for females are frequently low, but they range from 800 to 1500 mg/d (5). The percentage of adolescents in 20 countries meeting or exceeding country-specific calcium recommendations was 65% for males and 50% for females (6).