Dean C. Kramer: Falling short about vitamin D
Published: Monday, January 10, 2011 at 6:01 a.m.
Last Modified: Friday, January 7, 2011 at 12:13 a.m.
The Dec. 26 article titled “Vitamin D Falls Short” itself falls short. In many instances, the information printed is misleading or incomplete. Some of the questions posed require, therefore, more information.
The article asks: How much vitamin D did the experts say is necessary?
The committee of the Institute of Medicine felt that a daily dose of 400 to 800 International Units of vitamin D was adequate, depending on a person's age.
There are other experts in the field of vitamin D metabolism who would take issue with this conclusion arguing that vitamin D is, in fact, a hormone, part of the endocrine system, just like insulin and thyroid are hormones and that the amount of vitamin D that an individual requires should be based on measurement of blood levels.
The amount of vitamin D to be taken should be whatever amount is necessary to achieve optimum blood levels; whether that dose is 400 International Units or 10,000 International Units a day.
The article further poses the question: “I was told I was deficient in vitamin D. Is it true?”
Although individuals are advised to take enough vitamin D to bring their blood levels up to “normal” or optimal levels, there is no agreement among experts on what constitutes a “normal” blood level.
After critiquing the available research data, the committee of the Institute of Medicine was only willing to define vitamin D sufficiency as the amount of vitamin D needed to maintain bone calcification.
A substantial number of vitamin D experts take issue with this conservative position, feeling that levels of sufficiency should be set at higher levels than those recommended by the committee citing the potential benefit of vitamin D in other conditions. The committee was unwilling to adopt this position.
The confusion is further compounded by the fact that there are no universally accepted standards for the measurement of vitamin D. Different laboratories use differing methods for determining vitamin D, which cannot be compared to each other and sometimes test for different indicators of vitamin D deficiency.
Until the experts agree on what the “normal” level of vitamin D should be, and uniform standards and methods for determining blood levels are adopted, the concept of what constitutes vitamin D deficiency will remain controversial.
The article presents the question: Are there any groups of people for whom the need for vitamin D supplementation is likely to be higher? And it states that “breast milk is not a source of vitamin D.” Current research would suggest otherwise.
Dr. Michael Holick, pediatrician, researcher, and expert in vitamin D metabolism, at the University of South Carolina has clearly shown that if the pregnant mother gets sufficient sun exposure or vitamin D supplementation during her pregnancy that her breast milk will contain adequate amounts of vitamin D.
The article asks the question: Is there such a thing as too much vitamin D? The answer given is that “taking more than 4000 International Units of vitamin D is risky.”
Certainly, taking too much vitamin D may lead to toxicity, again emphasizing that the correct dosing of vitamin D should be based on accurate blood analysis and not on a “one size fits all” approach. What may be a toxic dose for one individual may be a therapeutic dose for another.
No responsible expert in vitamin D metabolism would argue that vitamin D is a “cure-all.”
However, we do know that vitamin D targets receptors in multiple body organs in addition to the bony skeleton and affects over 2,000 different genes in the body thus making it reasonable to believe that vitamin D has more of a role in bodily function than just bone calcification, the only role that the committee of the Institute of Medicine was willing to accept.
The best that can be said is that present day knowledge about this hormone is incomplete but that vitamin D shows future promise for “curing” more than our bones.
Until well designed studies can delineate the complete role of vitamin D and its effect on vitamin D receptors, a sensible approach to using vitamin D supplements should be based on accurately measured blood levels performed in laboratories with defined standards and controls and interpreted by providers who have studied and understand the extensive literature surrounding this hormone.
Dean C. Kramer is a physician who lives in Gainesville.
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