Dietary Reference Intakes for Calcium and Vitamin D (2011) / Chapter Skim
Currently Skimming:
8 Implications and Special Concerns
8 Implications and Special Concerns
Pages 479-512
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From page 479... ...
and to alert users of the DRI reference values to implications of the assessors' work and to related special issues. This chapter reflects the risk characterization step of the risk assessment approach and is organized to provide: a brief summary of the assessment; discussions about the implications of the committee's work for stakeholders; and discussions to highlight population segments and conditions of interest relative to calcium and vitamin D nutriture.
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From page 480... ...
If supplements are needed to ensure adequate calcium intake, it would appear that lower dose supplements should be considered. Many older women have baseline calcium intakes that are close to or just below requirements, and therefore the practice of calcium supplementation at high levels may be unnecessary.
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From page 481... ...
There is also some limited evidence that the long-term use of calcium supplements may increase the risk for cardiovascular disease. Although no attempt was made to compare systematically the data used for the North American population that is the subject of this report with data from other countries focused on persons who are genetically and environmentally different from those in the United States and Canada, it should be recognized that calcium requirements may be subject to a variety of factors that have not yet been fully elucidated and so therefore cannot yet be integrated into DRI reviews.
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From page 482... ...
Specific research recommendations for the future development of DRIs related to calcium and vitamin D are presented in Chapter 9. Assumption of Minimal Sun Exposure The committee's assumption of minimal sun exposure is a markedly cautious approach given that the vast majority of North Americans appear to obtain at least some vitamin D from inadvertent or deliberate sun exposure.
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From page 483... ...
The evidence to indicate that the synthesis of vitamin D from sun exposure is subject to a feedback loop that precludes toxicity from sun exposure is reassuring and, when coupled with the checks and balances introduced into the DRI development process, makes it very unlikely that consumption of the DRI levels of vitamin D, even if combined with high levels of sun exposure, will be problematic to the general population. However, given that many North Americans appear to obtain at least some vitamin D from inadvertent or deliberate sun exposure, there are implications for the interpretation of intake levels of the vitamin.
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From page 484... ...
physiologi cally serves as a prohormone introduced a myriad of variables and feedback loops related to its health effects; • The paucity of data and resulting uncertainty concerning sun ex posure that confound interpretation of the dose–response relation ship between intakes of vitamin D and various health outcomes. This, coupled with the apparent contribution of sun exposure to overall vitamin D nutriture in North American populations, leads to an inability to characterize and integrate sun exposure with in take recommendations as much as may be appropriate, given the concern for skin cancer risk reduction, which must be paramount.
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From page 485... ...
. DRI development fundamentally requires elucidation of dose–response relationships and benefits from data of high quality obtained in randomized controlled trials.
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From page 486... ...
The committee found all of the above findings to be the case for nonskeletal health outcomes for vitamin D, as the discussions of the strength, consistency, and causality of the evidence demonstrate in Chapter 4. Finally, an important uncertainty focuses on the issue of excess intake.
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From page 487... ...
Failure to achieve such serum concentrations place persons at greater risk for less than desirable bone health as manifested by, depending upon age, increased rates of bone accretion, bone mineral density, and fractures. Use of higher than appropriate cut-points for serum 25OHD levels would be expected to artificially increase the estimates of the prevalence of vitamin D deficiency.
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From page 488... ...
. As an overall result of these discussions, DRI development is now placed more clearly in the context of the risk assessment approach -- that is, an organizing framework for conducting evaluations with public health implications often made with evidentiary uncertainties.
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From page 489... ...
• With the exception of the inclusion of osteoporosis within the bone health measures, the existing data precluded the use of a chronic disease such as cancer or heart disease as an indicator for DRI development. However, had it been possible, this DRI process would have benefited from guidelines specifying what, if any, dif ferences may apply to using chronic disease endpoints versus other types of endpoints for DRI development (gap issue number 4-4 2 in Taylor, 2008)
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From page 490... ...
Although these and other studies have suggested that total body mass contributes to bone density and would appear to support the role of increased weight-bearing activity as a factor positively influencing bone density (Prentice et al., 1991; Khosla et al., 1996; Wortsman et al., 2000; Finkelstein et al., 2002, 2008) , more recent studies lead to further ques 3"There is broad interest in addressing the AIs as a component of the DRI values, but no clear path has emerged in terms of clarifying, adapting or eliminating AIs.
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From page 491... ...
(2007) observed that when the effect of mechanical loading from high body weight on bone density was statistically controlled, fat mass was inversely correlated with bone mineral content.
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From page 492... ...
. Persons Experiencing Reduced Vitamin D Synthesis from Sun Exposure The DRIs for vitamin D established in this report are based on the assumption of minimal sun exposure.
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. There are no data in this regard for other ethnic groups with dark skin, such as South Asians, so firm conclusions about their risk related to bone health cannot be drawn.
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From page 494... ...
All patients were primarily breast-fed for more than 11 months, with minimal intake of dairy products and without vitamin D supplementation. Breast milk, is of course, not a source of vitamin D for infants.
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From page 495... ...
In this case, the authors implicated both low calcium intake as well as marginal vitamin D nutriture in rickets. A recent 2-year survey of Canadian pediatricians found the incidence of rickets in their patients to be 2.9 per 100,000; the mean age at diagnosis was 1.4 years (range of 2 weeks to 6.3 years)
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From page 496... ...
The newly established DRI values assume minimal sun exposure, and therefore vitamin D intake need not be increased above this level for normal persons living in urban settings and spending time primarily indoors. However, data for institutionalized, frail older persons suggest a propensity for lower serum 25OHD levels generally.
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From page 497... ...
, appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful and nutritionally adequate. The North American prevalence of lactose intolerance, a clinical syndrome characterized by diarrhea, bloating and/or flatulence following consumption of lactose, is challenging to determine because the parameters surrounding lactose intolerance, lactose malabsorption, and lactase non-persistence are not well defined, and frequent self-diagnosis occurs (Brannon et al., 2010; Suchy et al., 2010)
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From page 498... ...
. Changes in Dietary Patterns of Indigenous Canadian Populations Among the indigenous Canadian populations, switching from a traditional diet that contains vitamin D–rich foods to a westernized diet may increase the likelihood of vitamin D deficiency, especially if UVB exposure is limited or avoided.
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From page 499... ...
. This research group also surveyed indigenous women of reproductive age from various communities in the Canadian Arctic and found the mean daily intakes of vitamin D to be 456 IU/day in Inuit from Qikiqtarjuaq, 364 IU/day in Inuit from 18 other communities, and 228 IU/day in a combined data set of Dene, Métis, and Yukon First Nations.
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From page 500... ...
Although the assumption of minimal sun exposure underpinning the DRI values may not entirely align with this group of people who may experience considerable sun exposure in the summer, ensuring that the diet meets the DRI values should provide assurances that risk of vitamin D deficiency has been greatly reduced. Use of Calcium Supplements The forms and nature of calcium supplements have been discussed in Chapter 2, and their possible role in kidney stone formation as well as the emerging data regarding possible adverse cardiovascular effects have been outlined in Chapter 6.
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From page 501... ...
has been hypothesized to reduce bone resorption and preserve bone density in premenopausal and postmenopausal women. This concept was based on clinical and observational evidence that ethinyl estrogen–based hormone replacement therapy reduced risk for osteoporosis in postmenopausal women (Zittermann, 2000)
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From page 502... ...
Although this study did not differentiate between hormone replacement therapy alone and therapy combined with vitamin D and calcium supplementation, it did suggest an effect of increasing bone density and bone markers in older women who received the combination therapy compared with those who received vitamin D and calcium supplementation alone. A randomized, double-blind, placebo-controlled trial of OC therapy either alone or combined with calcitriol therapy found a significant increase in bone density and reduction in bone resorption at the hip compared with OC therapy alone in postmenopausal women (ages 65 to 77 years)
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From page 503... ...
. Given the variability in all the study outcomes reviewed by the committee and the unresolved question of the effect of age and endogenous estrogen status on the ability of OCs to preserve bone density or prevent bone resorption, specific recommendations to address the impact of OCs with or without vitamin D and calcium supplementation for both premenopausal and postmenopausal women cannot be offered at this time.
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From page 504... ...
. techniques of the effects of vitamin D on calcium absorption in premature infants, nor could such studies be possible practically or ethically.
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From page 505... ...
Altering the fat blend of infant formula to more closely resemble that of human milk may also enhance mineral absorption in premature infants (Carnielli et al., 1995; Lucas et al., 1997) " (Abrams, 2005)
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1992. Net calcium absorption in premature infants: results of 103 metabolic balance studies.
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2002. Ethnic variation in bone density in premenopausal and early perimenopausal women: effects of anthropometric and lifestyle factors.
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2000. Dietary Reference Intakes: Applications in Dietary Assessment.
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2006. Effect of oral contraceptives and hormone replacement therapy on bone mineral density in premenopausal and perimenopausal women: a sys tematic review.
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1988. Mineral balance studies in very low birth weight infants fed human milk.
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2009. Dietary reference intakes for vitamin D: jus tification for a review of the 1997 values.
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From page 512... ...
2000. Decreased urinary calcium loss and lower bone turnover in young oral contraceptive users.
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