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Type: Thesis
Title: Studies on the Relationship between Dietary Calcium and Bone Mineral Homeostasis in Post-menopausal Women
Author: Thomas, Sunethra Devika Chin
Issue Date: 2016
School/Discipline: Adelaide Medical School
Abstract: There is a considerable body of evidence to suggest that osteoporosis is the index disease of calcium deficiency, in both humans and animals. In addition, menopause or oophorectomy has been shown to affect bone metabolism such that a rise in the rate of bone resorption leads to post-menopausal osteoporosis. If this is the case then increasing dietary calcium intake or supplementation with calcium will result in reducing the incidence of osteoporosis in post-menopausal women. The current study was conducted to investigate the relationship between habitual calcium intake and the rate of bone loss in post-menopausal women. Volunteers were recruited from the community to participate in a 2 year prospective study. A validated self-administered questionnaire was used to estimate total daily calcium intake in the subjects. Subjects were divided into tertiles according to calcium intakes. Six monthly bone density scans were performed of the lumbar spine, hip and forearm and the rate of decline in bone density for each site was calculated. Biochemical markers of bone metabolism at baseline were measured. The mean calcium intake was 1114 mg/d (300 – 2589mg/d). Only 10% of the women met their recommended daily intake (RDI) of calcium from their diet alone. When calcium supplements were considered (42% were taking supplements) 31% of women met their RDI. About 84% had serum 25OHD levels >50 nmol/L. Serum PTH was related to calcium intake, C-terminal telopeptides (CTX) and age. Although the relationship between serum PTH and 25OHD was not significant, PTH and CTX tended to be higher in those with low serum 25OHD within each tertile of calcium intake. In addition, women with lower calcium intake were heavier, while an inverse relationship was observed between 25OHD and fasting glucose. The prevalence of osteoporosis in the study group was much lower than that reported in previous surveys in Australian post-menopausal women, however, is consistent with the prevalence reported in health statistics for the wider community. The rate of loss of bone density at the ultradistal forearm fell significantly in women on lower calcium diets compared to higher calcium diets although no significant relationship was demonstrated between the rate of bone loss at the lumbar spine or the hip and calcium intake. This significant relationship at the ultradistal forearm site may be because of the greater proportion of trabecular bone at this site. Feedback on the bone density result was given to the subjects immediately after the baseline bone density measurement. The change in calcium intake after 12 months for women with osteoporosis or osteopenia was not significant suggesting that the feedback on bone density did not have an impact on dietary intakes or habits. The acute biochemical effects of calcium supplementation with or without vitamin D were examined in a group of vitamin D deficient women (serum 25OHD <50 nmol/L). Suppression of PTH and CTX was more effective when calcium was given with vitamin D. When the acute biochemical effects of calcium carbonate and citrate supplements were compared, citrate was found to be more effective than carbonate in suppressing bone resorption markers. Women with metabolic syndrome appear to be able to respond more favourably to a higher dietary calcium content that those without the metabolic syndrome. The findings of this study confirm that calcium intake, even in a relatively healthy and health conscious cohort of postmenopausal women is linked to the rate of bone loss, at least in trabecular bone (ultradistal forearm). However the influence of calcium intake on the bone density at other sites may be influenced by a myriad of other metabolic and endocrine factors, including metabolic syndrome. Data from this study confirm a probable link between energy and bone mineral metabolism. This knowledge may be harnessed to exploit the potential of adequate dietary calcium to improve bone health.
Advisor: Morris, Howard A
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 2017
Keywords: Osteoporosis
Dietary calcium
Bone loss
Bone density
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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