logical evidence of osteomalacia more likely in patients with hip fracture than those without hip fracture (Hoikka et al., 1982; Lips et al., 1982; von Knorring et al., 1982; Wilton et al., 1987; Diamond et al., 1998; LeBoff et al., 1999). Osteomalacia was also seen on bone biopsy in about 4 to 5 percent of general medical and geriatric patients who had not suffered a fracture (Anderson et al., 1966; Stacey and Daly, 1989). Of 111 women with postmenopausal vertebral compression fractures attributed to osteoporosis, 8 percent had evidence of osteomalacia (Avioli, 1978). Overall, these data suggest that the contribution of osteomalacia to fragility may be more significant than previously realized: 30 to 40 percent of hip fractures may be due to frank osteomalacia not osteoporosis; the remaining 60 to 70 percent of hip fractures may represent a spectrum that includes earlier stages of osteomalacia/demineralization due to inadequate calcium/vitamin D as well as osteoporosis. These data may also explain why vitamin D supplementation was found to effectively prevent hip fractures in an elderly population (Chapuy et al., 1992): it could be healing various degrees of underlying osteomalacia in the hip.
Calcium absorption and serum 25OHD As described earlier, studies of serum 25OHD concentrations and calcium absorption in adults (mostly in postmenopausal women and older men) have suggested that adequate calcium absorption occurs in the range of 30 to 50 nmol/L serum 25OHD for most persons. Fractional calcium absorption generally does not appear to increase with serum 25OHD concentration levels above 50 nmol/L. In addition, osteomalacia as explored in one study is not found to be meaningfully present until levels of serum 25OHD are at least below 30 nmol/L.
POTENTIAL INDICATORS FOR PREGNANCY: CALCIUM For the majority of women, pregnancy comes at a period of life when the mother’s body is normally experiencing bone maintenance. Key physiological changes during pregnancy, mediated by hormonal action, assure delivery of adequate calcium to meet the needs of the fetus, as discussed earlier (e.g., Kovacs and Kronenberg, 1997; Prentice, 2003; and Kovacs, 2008). These key changes also affect the utility of the bone health indicators detailed above for assessing dietary calcium needs. Potential indicators for calcium requirements during pregnancy are discussed below.
Calcium absorption Absorption efficiency doubles during pregnancy in adults (Heaney and Skillman, 1971; Kent et al., 1991) and adolescents (O’Brien et al., 2003). Calcium absorption is, thus, informative in the DRI development for pregnancy.
Calcium balance Pregnant women are in positive calcium balance early in pregnancy as indicated by the measures of hypercalciuria and direct measurement (Heaney and Skillman, 1971). However,