The second part was a nested case-control study on the risk factors for hip fracture. Cases were mostly postmenopausal women with first hip fracture within 2 to 64 months after entry into the large cohort study, or 5 to 67 months after the mid-point of the recalled dietary assessment. Four matched control subjects were selected for each case. A total of 247 cases and 873 control subjects completed the study. Univariate and multivariate conditional logistic regression analysis showed a dose-dependent increase in the risk of hip fracture with each 0.5 mg/day increment in reported retinol intake above 0.5 mg/day (baseline). The odds ratio was 2.05 (95 percent confidence interval, 1.05–3.98) at intakes above 1.5 mg/day.

In contrast to the results of Melhus and coworkers (1998), which suggest that risk of bone mineral loss and hip fracture occurs at estimated intakes above 1.5 mg/day, two U.S. studies provide no evidence of increased bone mineral loss in women with intakes of preformed vitamin A up to 1.5 to 2.0 mg/day (Freudenheim et al., 1986; Houtkooper et al., 1995). Freudenheim and coworkers (1986) evaluated the correlation between mean 3-year vitamin A intakes ranging from approximately 2 to 3 mg/day and rates of change in BMD in 84 women, 35 to 65 years of age (17 pre- and 67 postmenopausal). No consistent relationship was reported between vitamin A intake and the rate of bone mineral content loss in pre- and postmenopausal women. The single subject who showed rapid bone mineral loss with very high vitamin A intake also appeared to have consumed large amounts of other micronutrients as well, obscuring the significance of this relationship. Further, this study suffers from a small sample size in each of the four key groups (i.e., pre- and postmenopausal women by calcium supplement status), making correlations of potential nutritional or pathological importance indeterminate.

Houtkooper and coworkers (1995), in a longitudinal study of 66 women 28 to 39 years of age, showed that vitamin A intake was significantly associated with the increased annual rate of change in total body BMD. The mean rate of change in total body BMD over the 18-month study was negative, although several sites (lumbar spine, trochanter, and Ward’s triangle) showed small positive slopes. The estimated mean intake of preformed vitamin A from the diet was 1,220 ± 472 (standard deviation [SD]) μg/day. The estimated vitamin A intake from provitamin A carotenoids was 595 ± 352 (SD) μg/day. In multivariable regression models that included covariables for body composition and treatment (exercise versus sedentary) status, the slopes for vitamin A and carotene (two separate models) were both positive [b = 0.007 and 0.008 mg/(cm²-year)]

Front Matter (R1-R24)

Summary (1-28)

1 Introduction to Dietary Reference Intakes (29-43)

2 Overview and Methods (44-59)

3 A Model for the Development of Tolerable Upper Intake Levels (60-81)

4 Vitamin A (82-161)

5 Vitamin K (162-196)

6 Chromium (197-223)

7 Copper (224-257)

8 Iodine (258-289)

9 Iron (290-393)

10 Manganese (394-419)

11 Molybdenum (420-441)

12 Zinc (442-501)

13 Arsenic, Boron, Nickel, Silicon, and Vanadium (502-553)

14 Uses of Dietary Reference Intakes (554-579)

15 A Research Agenda (580-586)

Appendix A Origin and Framework of the Development of Dietary Reference Intake (587-590)

Appendix B Acknowledgments (591-593)

Appendix C Dietary Intake Data from the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994 (594-643)

Appendix D Dietary Intake Data from the Continuing Survey of Food Intakes by Individuals (CSFII), 1994-1996 (644-653)

Appendix E Dietary Intake Data from the U.S. Food and Drug Administration Total Diet Study, 1991-1997 (654-673)

Appendix F Canadian Dietary Intake Data, 1990 (674-679)

Appendix G Biochemical Indicators for Iron, Vitamin A, and Iodine from the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994 (680-691)

Appendix H Comparison of Vitamin A and Iron Intake and Biochemical Indicators from the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994 (692-696)

Appendix I Iron Intakes and Estimated Percentile of the Distribution of Iron Requirements from the Continuing Survey of Food Intakes by Individuals (CSFII), 1994-1996 (697-703)

Appendix J Glossary and Acronyms (704-708)

Appendix K Conversion of Units (709-709)

Appendix L Options for Dealing with Uncertainties (710-714)

Appendix M Biographical Sketches of Panel and Subcommittee Members (715-728)

Index (729-769)

Summary Table, Dietary Reference Intakes: Recommended Intakes for Individuals, Vitamins (770-771)

Summary Table, Dietary Reference Intakes: Recommended Intakes for Individuals, Elements (772-773)