Chemistry Reference
In-Depth Information
appears likely if calcium intake is consistent with usual average intakes in the
United States (Abrams, 2005). For example, a recent meta-analysis of 19
randomized controlled trials involving 2859 children (aged 3-18 yr) examined
the effects of the addition of 300-1200 mg calcium per day from supplemen-
tation or dairy products (Winzenberg et al., 2006). This analysis concluded
that there was no significant persistent effect of calcium supplementation on
femoral neck or lumbar spine bone mineral density (BMD). A small long-
term effect of supplementation on BMD in the upper limb seemed unlikely to
reduce the risk of fracture, either in childhood or in later life, to a degree of
major public health importance. During sexual maturation (
9-18 yr), cal-
cium retention increases to a peak and then declines, a physiological phenom-
enon that complicates derivation of estimates of calcium needs. The AI for
this age group has been estimated from three major lines of evidence: (1) a
factorial approach (summation of calcium needs for growth plus calcium
losses with adjustments for absorption), (2) calcium retention to meet peak
bone mineral accretion and (3) clinical trials in which bone mineral content
was measured in response to variable calcium intakes. There is no consensus
as to when peak bone mass occurs (Nilas, 1993) and there may be an overall
increase, not decrease, in total skeletal mass of about 4% between 18 and 50 yr
(Matkovic et al., 1994). The AI for calcium for men and women aged 19-50 yr
is based on balance studies and bone mineral density data.
It is well recognized that calcium has a limited role in maintaining bone
health because calcium adequacy alone does not provide full protection
against bone loss (Shapiro and Heaney, 2003) associated with age and meno-
pause (Heaney, 2006). In perimenopausal women, significant metacarpal and
lumbar bone loss occurs even with supplements of 1000 or 2000 mg calcium
per day (Elders et al., 1991). Spinal BMD lost at menopause can be attributed
completely to estrogen deprivation, and femoral neck losses are a composite
of estrogen deprivation and age-related loss (Recker et al., 2000). The AI for
calcium for men and women aged
51 is based on the assumption that
individuals in this age range would have calcium needs somewhat higher
than that of the 19- through 30-yr age group (Food and Nutrition Board:
Institute of Medicine, 1997). However, among the several studies of calcium
intake and fracture risk, no consistent association has been demonstrated
between reported calcium intake over periods of up to 10 yr and fractures
(Cumming and Nevitt, 1997; Dawson-Hughes, 2006; Jackson et al., 2006), the
only sequela of importance in osteoporosis. Also, most (Kochersberger et al.,
1990; Chapuy et al., 1992; Chevalley et al., 1994; Dawson-Hughes et al., 1997;
2000; Hitz et al., 2007), but not all (Phang et al., 1969), studies on adults
indicating a positive influence of high dietary Ca in reducing the rate of bone
remodeling were confounded by the presence of vitamin D as an experimental
co-variable.
