The Nation's Health + [vitamin D]

Why an RDA for vitamin D?

The Food and Nutrition Board (FNB) of the Institute of Medicine is charged with setting the values for the Recommended Daily Allowances of various essential nutrients. However, when it comes to vitamin D, the FNB decided that "evidence is insufficient to develop an RDA and [an Adequate Intake, AI] is set at a level assumed to ensure nutritional adequacy."

The National Institutes of Health Office of Dietary Supplements lists the AI's for various groups of people:

14-18 years
Male 200 IU
Female 200 IU

19-50 years
Male 200 IU
Female 200 IU

51-70 years
Male 400 IU
Female 400 IU

71+ years
Male 600 IU
Female 600 IU

A reconsideration is apparently being planned in near-future that will (hopefully) incorporate the newest clinical data on vitamin D.

My question: Who cares what the FNB decides? Let me explain.

I monitor blood levels of 25-hydroxy vitamin D to assess the 1) starting level of vitamin D without supplementation, and 2) levels while on supplementation, preferably every 6 months (during sunny weather, during cold weather). I have done for the past 3 years in over 1000 people.

The requirement for vitamin D dose in adults, in my experience, ranges from as low as 1000 units per day to as high as 20,000 units per day, rarely more. The vast majority of women require 5000 units per day, males 6000 units per day to maintain a blood level in the desirable range. (I aim for 60-70 ng/ml.) A graph of the distribution of vitamin D needs in my area (Milwaukee, Wisconsin) is a bell curve, a curve more heavily weighted towards the upper vitamin D dose range.

Need for vitamin D to achieve the same blood level is influenced by age, sex, body size, race, presence or absence of a gallbladder, as well as other factors. But needs vary, even among similar people. For instance, a 50-year old woman weighing 140 lbs might need 4000 units per day to achieve a blood level of 25-hydroxy vitamin D of 65 ng/ml. Another 50-year old woman weighing 140 lbs might need 8000 units to achieve the same level, and 4000 units might increase her level to only 38 ng/ml. Two similar women, very different vitamin D needs. The differences can be striking.

Being a hormone --not a vitamin, as it was incorrectly labeled--vitamin D needs to be tightly regulated. We should have neither too little nor too much. I would liken it to thyroid hormones, which need to be tightly regulated for ideal health.

Now the FNB, in light of new data, wants to set new AI's, or even RDA's, for vitamin D for the U.S. This is an impossible--impossible --task. There is no way a broad policy can be crafted that serves everyone. It is impossible to state that all men or women, categorized by age, require X units vitamin D. This is pure folly and it is misleading.

The only rational answer for the FNB to provide is to declare that:

It is not possible to establish the precise need for vitamin D in a specific individual because of the multiplicity of factors, only some of which are known, that determine vitamin D needs. Individual need can only be determined by assessing the blood level of 25-hydroxy vitamin D prior to initiation of replacement and periodically following replacement to assess the adequacy of replacement dose. Continuing reassessment is recommended (e.g., every 6-12 months), as needs change with weight, lifestyle, and age.

Sure, it adds around $100-150 per year per person for lab testing to assess vitamin D levels. But the health gains made--reduced fractures, reduced incidence of diabetes, reduced colon, breast, and prostate cancer, less depression, reduced heart attack and heart procedures--will more than compensate.