BONE TURNOVER RESPONSE TO CHANGES IN CALCIUM INTAKE IS ALTERED IN GIRLS AND ADULT WOMEN IN FAMILIES WITH HISTORIES OF OSTEOPOROSIS

Heredity and environmental factors contribute to the development of os teoporosis, Because calcium is the major mineral in bone and adolescen ce is a key period in bone acquisition, we hypothesized that bone turn over would be less responsive to alterations in dietary calcium intake in both girls and adult women from families with histories of osteopo rosis, To address this issue, we studied calcium kinetics in the mater nal grandmother (age range 56-81 years), mother (age range 32-47 years ), and granddaughter (age range 8-15 years) in 10 multigenerational fa milies, In five families,the mother and/or grandmother had osteoporosi s (bone mineral density greater than or equal to 2 SD below the age-sp ecific mean), To examine both active and passive calcium absorption, f amilies consumed low-(279 +/- 64 mg/day) and high-(1580 +/- 385) calci um diets for 10 days prior to administration of oral (Ca-46) and intra venous (Ca-42) stable isotopes, Using repeated measures analysis of va riance, fractional calcium absorption, true calcium absorption, bone c alcium deposition, and the balance in bone calcium turnover were all s ignificantly affected by diet (p < 0.01), Females from nonosteoporotic families had decreased bone calcium resorption with little change in bone calcium deposition during the high-calcium study, In contrast, gi rls and adult women from osteoporotic families had increased both bone calcium deposition and resorption during the high-calcium period, lea ding to a less positive balance in bone calcium turnover, A significan t interaction between bone status and diet was found for bone calcium resorption (p < 0.05) and approached significance for bone calcium dep osition (p < 0.07), effects which were independent of generation, We c onclude that girls and women from osteoporotic families have a signifi cantly altered bone turnover response to acute changes in calcium inta ke.