This article summarizes the new 2011 report on dietary requirements for calcium and vitamin D from the Institute of Medicine (IOM). An IOM Committee charged with determining the population needs for these nutrients in North America conducted a comprehensive review of the evidence for both skeletal and extraskeletal outcomes. The Committee concluded that available scientific evidence supports a key role of calcium and vitamin D in skeletal health, consistent with a cause-and-effect relationship and providing a sound basis for determination of intake requirements. For extraskeletal outcomes, including cancer, cardiovascular disease, diabetes, and autoimmune disorders, the evidence was inconsistent, inconclusive as to causality, and insufficient to inform nutritional requirements. Randomized clinical trial evidence for extraskeletal outcomes was limited and generally uninformative. Based on bone health, Recommended Dietary Allowances (RDAs; covering requirements of ≥97.5% of the population) for calcium range from 700 to 1300 mg/d for life-stage groups at least 1 yr of age. For vitamin D, RDAs of 600 IU/d for ages 1–70 yr and 800 IU/d for ages 71 yr and older, corresponding to a serum 25-hydroxyvitamin D level of at least 20 ng/ml (50 nmol/liter), meet the requirements of at least 97.5% of the population. RDAs for vitamin D were derived based on conditions of minimal sun exposure due to wide variability in vitamin D synthesis from ultraviolet light and the risks of skin cancer. Higher values were not consistently associated with greater benefit, and for some outcomes U-shaped associations were observed, with risks at both low and high levels. The Committee concluded that the prevalence of vitamin D inadequacy in North America has been overestimated. Urgent research and clinical priorities were identified, including reassessment of laboratory ranges for 25-hydroxyvitamin D, to avoid problems of both undertreatment and overtreatment.

It is well-recognized that young women with untreated premature ovarian failure (POF) are at increased risk of osteoporosis and bone fracture. Large, randomized trials have demonstrated that hormone replacement therapy with estrogen/progesterone in postmenopausal women can dramatically improve bone mineral density (BMD) and reduce fracture risk; however, there are little data on the effect of hormone replacement in young women with POF. At present, young women with POF are given either combined hormone replacement treatment or physiologic SSR (pSSR) consisting of combined transdermal estradiol and vaginal progesterone replacement regimens.This open-label, randomized controlled crossover pilot trial was designed to determine whether a regimen of pSSR could improve skeletal health among young women with POF caused by a variety of reasons. A total of 34 patients were randomized to receive a 4-week cycle of either pSSR (transdermal estradiol 100 g daily for week 1 and 150 g for weeks 2-4, with progesterone 200 mg twice daily for weeks 3-4) or standard hormone replacement therapy (sHRT) (oral ethinyl estradiol 30 g and norethisterone 1.5 mg daily for weeks 1-3, followed by 7 "pill-free" days for 12 months). Dual-energy x-ray absorptiometry was used to measure BMD at baseline and after each 12-month treatment period. During the study period, blood samples were collected for hormonal measurements and for markers of bone formation (bone alkaline phosphatase and procollagen type I aminoterminal propeptide) and bone resorption (CrossLaps [cross-linked C-terminal telopeptide of type I collagen]) before and after each washout period, and at 3, 6, and 12 months. Of the 34 women, 18 (mean age 27; range, 19-39 years) completed the study. LH (luteinizing hormone) and FSH (follicle-stimulating hormone) were decreased to a similar extent by both pSSR and sHRT. Treatment with pSSR increased the mean baseline lumbar spine BMD z-score by ϩ0.17 (95% confidence interval: ϩ0.07 to ϩ0.27; P ϭ 0.003), whereas there was no significant increase in response to sHRT (ϩ0.07, with a 95% confidence interval: Ϫ0.03 to ϩ0.18; P ϭ 0.2). During pSSR, the increment in lumbar spine BMD z-score was positively associated with estradiol (r ϭ ϩ0.49; P ϭ 0.04) and inversely associated with FSH (r ϭ Ϫ0.65; P ϭ 0.004). Both bone alkaline phosphatase and procollagen type I amino-terminal propeptide were increased significantly by pSSR ( ANOVA P Ͻ 0.001). In contrast, both of these bone formation markers were decreased by sHRT (P Ͻ 0.01). The bone resorption marker, CrossLaps, was suppressed by both regimens (P Ͻ 0.001). GYNECOLOGYVolume 66, Number 6 OBSTETRICAL AND GYNECOLOGICAL SURVEY

Significant controversy has emerged over the last decade concerning the effects of vitamin D on skeletal and nonskeletal tissues. The demonstration that the vitamin D receptor is expressed in virtually all cells of the body and the growing body of observational data supporting a relationship of serum 25-hydroxyvitamin D to chronic metabolic, cardiovascular, and neoplastic diseases have led to widespread utilization of vitamin D supplementation for the prevention and treatment of numerous disorders. In this paper, we review both the basic and clinical aspects of vitamin D in relation to nonskeletal organ systems. We begin by focusing on the molecular aspects of vitamin D, primarily by examining the structure and function of the vitamin D receptor. This is followed by a systematic review according to tissue type of the inherent biological plausibility, the strength of the observational data, and the levels of evidence that support or refute an association between vitamin D levels or supplementation and maternal/child health as well as various disease states. Although observational studies support a strong case for an association between vitamin D and musculoskeletal, cardiovascular, neoplastic, and metabolic disorders, there remains a paucity of large-scale and long-term randomized clinical trials. Thus, at this time, more studies are needed to definitively conclude that vitamin D can offer preventive and therapeutic benefits across a wide range of physiological states and chronic nonskeletal disorders.

During pregnancy and lactation, female physiology adapts to meet the added nutritional demands of fetuses and neonates. An average full-term fetus contains ϳ30 g calcium, 20 g phosphorus, and 0.8 g magnesium. About 80% of mineral is accreted during the third trimester; calcium transfers at 300-350 mg/day during the final 6 wk. The neonate requires 200 mg calcium daily from milk during the first 6 mo, and 120 mg calcium from milk during the second 6 mo (additional calcium comes from solid foods). Calcium transfers can be more than double and triple these values, respectively, in women who nurse twins and triplets. About 25% of dietary calcium is normally absorbed in healthy adults. Average maternal calcium intakes in American and Canadian women are insufficient to meet the fetal and neonatal calcium requirements if normal efficiency of intestinal calcium absorption is relied upon. However, several adaptations are invoked to meet the fetal and neonatal demands for mineral without requiring increased intakes by the mother. During pregnancy the efficiency of intestinal calcium absorption doubles, whereas during lactation the maternal skeleton is resorbed to provide calcium for milk. This review addresses our current knowledge regarding maternal adaptations in mineral and skeletal homeostasis that occur during pregnancy, lactation, and post-weaning recovery. Also considered are the impacts that these adaptations have on biochemical and hormonal parameters of mineral homeostasis, the consequences for long-term skeletal health, and the presentation and management of disorders of mineral and bone metabolism.

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