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Questions About Vitamin D And Calcium Supplements
2013-12-23 11:39   审核人:

"The message is that there are known "knowns." There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns. There are things we do not know we don't know."
Donald Rumsfeld, former United States Secretary of Defense

Over the last 10 to 15 years there has been a growing trend by health care providers to be concerned about deficiencies in vitamin D and calcium.  It has long been established that these nutrients are vital for bone health.  However, a large body of data has also demonstrated inverse correlations between levels of vitamin D and the incidence of a large number of conditions including cancer, cardiovascular disease, diabetes, immune and infectious disorders neuropsychological functioning and physical performance. The development of reliable assays for serum 25 (OH) vitamin D levels has allowed a more accurate estimation of total body vitamin D stores and facilitated the development of "cut-points" in the serum levels of 25 (OH) vitamin D.  These were identified by a variety of criteria and used to define states of sufficiency, insufficiency and deficiency. Both calcium and vitamin D supplements are readily available.  Almost all pharmacies currently stock both and it is relatively easy in the United States to obtain vitamin D preparations, without a prescription, containing as much as 5,000 IUs of vitamin D3.  It has also recently been conventional wisdom that these supplements were without significant risk. 

Now, the Institute of Medicine of the United States National Academy of Sciences has released a report on dietary reference intake recommendations for calcium and vitamin D that call into question many of our previously widely held views about these agents. The committee, which produced the report, reviewed over 1000 published papers on this topic, held public hearings and called upon numerous experts in this field. Some of their conclusions are the following:

1) The recommended dietary allowance (RDA) for calcium per day should range from 700 mg for individuals 1-3 years old to 1200 mg per day for 51 to 70 year old females and all individuals greater than 71 years old. Pregnant or lactating females aged 14 to 18 years old were assigned an RDA of 1300 mg per day.  The RDA is an estimation of the amount of supplement that needs to be consumed to fully meet the needs of 97.5% of the population.  The upper safe level of intake for calcium ranged from 2000 to 3000 mg per day.  It was not clear to the committee that supplementation above the RDA provided additional benefit.

2)  The RDA for vitamin D supplementation was designated as 600 IUs for all groups except individuals greater than 71 years old who were given an RDA of 800 IUs per day.  The upper safe daily level of intake for vitamin D was designated to range from 1000 units for 0 to 6 month old infants to 4000 units for all individuals greater than 9 years old.

3)  The report found no conclusive evidence to support the use of vitamin D supplementation to prevent or treat any condition other than the promotion of bone health.  While the committee found reports that vitamin D may be of importance for other health reasons, they concluded that the current data did not substantiate such claims.  However, it also did not rule them out. 

4)  The committee stated that they were concerned that "a considerable over-estimation of the levels of vitamin D deficiency in the North American population now exists due to the use by some of cut-points for serum 25 (OH) vitamin D levels that greatly exceed the levels identified in the report as consistent with the available data".  The committee's review of the data "suggests that persons are at risk of deficiency at serum 25 (OH) vitamin D levels of below 30 nmol/L (12 ng/mL). Some, but not all, persons are potentially at risk for inadequacy at serum 25 (OH) vitamin D levels between 30 and 50 nmol/L (12 and 20 ng/mL). Practically all persons are sufficient at serum 25 (OH) vitamin D levels of at least 50 nmol/L (20 ng/mL). Serum 25 (OH) vitamin D concentrations above 75 nmol/L (30 ng/mL) are not consistently associated with increased benefit. There may be reason for concern at serum 25OHD levels above 125 nmol/L (50 ng/mL)".

Clearly, these recommendations will provoke much discussion as they challenge many beliefs about these supplements. In the coming weeks a number of additional organizations, including the Professional Practice Committee of the ASBMR, will weigh in on these supplements. Whatever the final consensus view is or even if a consensus is ever possible will depend on additional studies that are designed to more clearly define the risks and benefits of the use of these supplements by the general population.

                                                                                                          Joe Lorenzo
                                                                                                          Farmington, CT, USA

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