Optimal Calcium Intake
National Institutes of Health
Consensus Development Conference Statement
June 6-8, 1994

Calcium and Health: Part 1   Calcium and Health: Part 2
Calcium and Health: Part 3   Calcium and Health: Part 4
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Part 4
Optimal Calcium Intakes (continued)
A great deal of recent data related to calcium intake and its effects on calcium balance, bone mass, and the prevention of osteoporosis was reviewed, with attention given to the calcium requirements over the life cycle. The current Recommended Dietary Allowances(RDA) (10th edition, 1989) for calcium intake were considered as reference levels and used as guidelines to determine optimal calcium intake in light of new data on calcium-related disorders.
 
Infants (Birth-12 Months) and Young Children
(1-10 Years) Calcium intake of exclusively breast-fed infants during the first 6 months of life is in the range of 250-330 mg/day, with a fractional calcium absorption between 55 and 60 percent. A lower fractional absorption of 40 percent is found with cow milk-based formulas. These formulas contain nearly twice the calcium content of human milk; this results in comparable calcium retentions of 150-200 mg/day from both formula and breast milk. Net calcium absorption from soy-based formulas is comparable to, or higher than, that of breast milk or cow milk formulas because of its considerably higher calcium content. For infants between the ages of 6 and 12 months, calcium intake ranges from 400 to 700 mg/day. On the basis of balance data, the current RDAs for calcium, 400 mg/day for infants from birth to 6 months and 600 mg/day for those from 6 to 12 months, seem sufficient to provide optimal calcium intake. However, special circumstances such as low birth weight may require higher calcium intake. Limited data from one recent study suggest that in children 6-10 years old, intake above 800 mg/day may lead to increased rates of bone accumulation. Coupled with calcium balance data, this suggests that an intake of greater than 800 mg/day may be optimal for this age group. It should also be noted that poor calcium nutrition in childhood may be related to development of enamel hypoplasia and accelerated dental caries.
 
Children and Young Adults (11-24 Years)
Calcium accumulation in bone during preadolescence is between 140 and 165 mg/day and may be as high as 400-500 mg/day in the pubertal period. Fractional intestinal absorption is very efficient and estimated to be approximately 40 percent. Peak adult bone mass, depending on the skeletal site examined, is largely achieved by 20 years of age, although important additional bone mass may accumulate through the third decade of life. Furthermore, cross-sectional studies reveal a small but positive association between life-long calcium intake and adult bone mass. Therefore, optimal calcium intake in childhood and young adulthood is critical to achieving peak adult bone mass. Recent evidence suggests that adding 500-1,000 mg/day to current calcium intake may, at least temporarily, increase bone accretion rates in preadolescent boys and girls. With this supplementation, total calcium intake in these studies exceeded the current RDA of 1,200 mg/day; however, it is unclear whether the effect on bone accretion rates persists beyond the reported 18-month to 3-year periods of treatment and whether these increased rates of bone formation translate into higher peak adult bone mass. Recent balance studies in adolescents indicate a calcium intake threshold in the range of 1,200-1,500 mg/day. Collectively, these data suggest that calcium intake in the range of 1,200-1,500 mg/day might result in higher peak adult bone mass. Additional research is necessary, particularly longitudinal, long-term dose-ranging studies of the effects of varying calcium intake on bone mass, to more precisely define optimal calcium intake for this age group. Importantly, population surveys of girls and young women 12-19 years of age show their average calcium intake to be less than 900 mg/day, which is well below the calcium intake threshold. The consequences of low calcium intake during this crucial period of rapid skeletal accrual raise concerns that achievement of optimal peak adult peak bone mass may be seriously compromised. Special education and public measures aimed at improving dietary calcium intake in this age group are essential.
 
Calcium Intake in Adults (25-65 Years of Age)
Once peak adult bone mass is reached, bone turnover is stable in men and women such that bone formation and bone resorption are balanced. In women, resorption rates increase and bone mass declines beginning with the fall in estrogen production that is associated with the onset of menopause. The decline in circulating 17-beta-estradiol is the predominant factor in the accelerated bone loss that begins after the onset of menopause and continues for 6-8 years. Unlike hormone replacement therapy, supplemental calcium during this initial phase will not slow the decline in bone mass due to estrogen deficiency. Although the effects of calcium can be shown more clearly in postmenopausal women after the period when the effects of estrogen deficiency are no longer dominant (approximately 10 years after menopause), it is likely that the early postmenopausal years are also an important time to ensure optimal calcium intake. Between 25 and 50 years of age, women who are otherwise healthy should maintain a calcium intake of 1,000 mg/day (Osteoporosis. NIH Consensus Statement 1984 Apr 2-4;5(3):1-6). For postmenopausal women who are receiving estrogen replacement therapy, a calcium intake of 1,000 mg/day is recommended to maintain calcium balance and stabilize bone mass. For postmenopausal women who do not take estrogen, it is estimated that a calcium intake of 1,500 mg/day may limit loss of bone mass, but should not be considered a replacement for estrogen. Therefore, recommended calcium intake for postmenopausal women up to 65 years of age is 1,000 mg/day in conjunction with hormonal replacement and 1,500 mg/day in the absence of estrogen replacement. Adult men also sustain fractures of the hip and vertebrae, although at a lower frequency than women. In several prospective and cross-sectional studies, hip fracture risk in men has been found to be inversely correlated with calcium intake. Although the data are less extensive in men than in women, the evidence in men suggests that inadequate calcium intake is associated with reduced bone mass and increased fracture risk. Available data, although sparse, indicate an optimal calcium intake among adult men similar to women, namely 1,000 mg/day.
 
Calcium Intake in Adults (Older Than 65 years)
In men and women 65 years of age and older, calcium intake of less than 600 mg/day is common. Furthermore, intestinal calcium absorption is often reduced because of the effects of estrogen deficiency in women and the age-related reduction in renal 1,25-dihydroxy vitamin D production. Calcium insufficiency due to low calcium intake and reduced absorption can translate into an accelerated rate of age-related bone loss in older individuals. Among the homebound elderly and persons residing in long-term care facilities, vitamin D insufficiency has been detected and may contribute to reduced calcium absorption. Calcium intake among women later in the menopause, in the range of 1,500 mg/day, may reduce the rates of bone loss in selected sites of the skeleton such as the femoral neck. (These findings also indicate that the calcium threshold for reducing bone loss may vary for different regions of the skeleton.) The physiology of calcium homeostasis in aging men over 65 is similar to that of women with respect to the rate of bone loss, calcium absorption efficiency, declining vitamin D levels, and changes in markers of bone metabolism. It seems reasonable, therefore, to conclude that in aging men, as in aging women, prevailing calcium intakes are insufficient to prevent calcium-related erosion of bone mass. Thus, in women and in men over 65, calcium intake of 1,500 mg/day seems prudent.
 
Pregnant and Lactating Women
The current RDA for calcium intake during pregnancy and lactation is 1,200 mg/day. Pregnancy represents a significant physiological stress on maternal skeletal homeostasis. A full-term infant accumulates approximately 30 grams of calcium during gestation, most of which is assimilated into the fetal skeleton during the third trimester. Available data suggest that, with pregnancy, no permanent decline in body calcium occurs if recommended levels of dietary calcium intake are maintained. There is no association between parity and bone mass. Furthermore, there is no evidence to support changing the current recommendation of calcium intake for well-nourished pregnant women. There is, however, a large population of pregnant women who are not ingesting sufficient calcium, especially those who are undernourished. These women need to be identified, and appropriate adjustments in their calcium intake should be made. Data are not available regarding the calcium requirement for pregnant women at the extremes of reproductive years, for those who experience nonsingleton births, and for those with closely spaced pregnancies. During lactation, 160-300 mg/day of maternal calcium is lost through production of breast milk. Longitudinal studies in otherwise healthy women demonstrate acute bone loss during lactation that is followed by rapid restoration of bone mass with weaning and the resumption of menses. Women who are lactating should ingest at least 1,200 mg of calcium per day. Lactating adolescents and young adults should ingest up to 1,500 mg of calcium per day.