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Which comes first, opinions or evidence?

Posted on: March 2, 2018   by  John Cannell, MD


I recently realized I sometimes form opinions before I have the evidence to support those opinions.  For example, I knew that identical twin studies from the 70s and also the last few years, have shown that some of our opinions are highly heritable. Modern genetic studies repeatedly show more than 50% of your political outlook is genetically determined. After learning that, I tried to rid myself of any political opinions.  I mean, how do I know if it’s just my genes talking?

I reluctantly concluded that having an opinion often comes before looking at the evidence; perhaps it is just human nature.  That upset me, so I looked for evidence of this in the scientific field.  The first place I looked were opinions about vitamin D, where I am aware of both the opinions and evidence.

I remember reading the American College of Obstetricians and Gynecologists (ACOG) 2011 Opinion # 495 about vitamin D and pregnancy. Essentially, their opinion was pregnant women don’t need to be routinely tested for vitamin D deficiency but, if – somehow – found deficient, seldom need more than 1,000-2,000 IU/day (25 – 50 mcg/day). Is that what the scientific evidence actually showed before 2011?

First, I tried to find out who actually authored that ACOG’ opinion. Well, after due diligence, I could not find who authored this opinion! Were any vitamin D experts included or even consulted? I asked the ACOG office, who first they ignored me and then refused to say.

I then did a search of all papers published on vitamin D and pregnancy from 1950 to 2010 (before the ACOG’s 2011 publication) and got 197 publications. I could not find any paper presenting evidence that vitamin D deficiency is not a problem nor one indicating it is harmful during pregnancy. However, a number of experts had concluded – before 2011 – that vitamin D deficiency during pregnancy was common – and a problem.  Here are the conclusions of some of the papers published prior to ACOG’s 2011 opinion.

Bodnar et al: “Our study suggests that black and white pregnant women residing in northern United States and their neonates are at high risk of vitamin D insufficiency, even when they regularly use a prenatal vitamin or multivitamin. Our data add to the growing body of research supporting assertions that the current vitamin D dietary intake recommendations are inadequate to meet the increased demands of pregnancy.”

Mulligan et al: “Vitamin D deficiency is common in pregnant women (5-50%).” and “Adverse health outcomes such as preeclampsia, low birthweight, neonatal hypocalcemia, poor postnatal growth, bone fragility, and increased incidence of autoimmune diseases have been linked to low vitamin D levels during pregnancy . . .”

Shin et al: “Vitamin D deficiency “during pregnancy” correlates with preeclampsia, gestational diabetes mellitus, and bacterial vaginosis, and an increased risk for C-section delivery.”

Dror et al: “It is evident that prior levels used to establish intake recommendations and vitamin D content of prenatal vitamin supplements (10 mcg/day) were too conservative.”

Robison et al: “Subjects with eclampsia were noted to have decreased total 25-OH-D levels relative to healthy control subjects “

How many of these papers did ACOG cite?  I couldn’t find that they cited any of them. Well, maybe the papers above all appeared in second class journals? No, they all appeared in reputable journals, sometimes in the two most prestigious such journals, The American Journal of Obstetrics and Gynecology and Obstetrics and Gynecology, which now have sixty-five and seventeen publications on vitamin D, respectively.

In researching this, I remembered that I had paid the 2009 ACOG journal (Green Journal) to publish an “advertisement” about vitamin D, and they graciously agreed. Then, when some of their members disagreed, ACOG let me respond for free. But then they changed their policies, precluding me from similar publications in the future.

What was my “advertisement trying to sell? The only thing I was trying to sell was an idea: obstetricians should diligently diagnose and adequately treat vitamin D deficiency in all pregnant women, thus heeding the 2008 guidance of the American Academy of Pediatrics:

“Given the growing evidence that adequate maternal vitamin D status is essential during pregnancy, not only for maternal well-being but also for fetal development, health care professionals who provide obstetric care should consider assessing maternal vitamin D status by measuring the 25-OH-D concentrations of pregnant women. On an individual basis, a mother should be supplemented with adequate amounts of vitamin D3 to ensure that her 25-OH-D levels are in a sufficient range (> 32 ng/mL). The knowledge that prenatal vitamins containing 400 IU of vitaminD3 have little effect on circulating maternal 25-OH-D concentrations, especially during the winter months, should be imparted to all health care professionals involved in the care of pregnant women”2  (page 1145).

This exercise led me to some questions:

  1. Had ACOG already formed their opinion before they looked at the evidence?
  2. Did ACOG only look at evidence that supported their opinion?
  3. Did ACOG ignore studies that indicated their opinion was wrong?
  4. Did ACOG include any vitamin D authorities when reaching their opinion?

Terrible, right?  Not really. The more I think about it, the more I’m afraid it’s just human nature. Remember, if more than 50% of your opinions are heritable, maybe ACOG’s opinion was just their genes talking.


Cannell, JJ. Opinions and evidence. The Vitamin D Council Blog & Newsletter, March 1, 2018.

2 Responses to Which comes first, opinions or evidence?

  1. IAW

    I am going to call it “Intellectual Arrogance”! Defined as “an individual that considers his/her intellect to be superior to others, his/her knowledge cannot be challenged and he/she judges others based on their intellect.”
    In my own words I think simply that because they learned in their lifetime that Vitamin D was to be feared, to back track now and “admit they were wrong” or “admit” they are wrong on the amount of Vitamin D it takes to be healthy, is simply too much for them to handle. They would have to admit they are wrong and they have “way too much pride” for that. Their “egos” are way too big to allow any of this!

  2. fredglass

    In 1882 Gilbert & Sullivan wrote a comic opera, Iolanthe whiich has the following line: “Nature always does contrive that every girl and boy that’s born into the world alive is either a little liberi or a little conservati.”

    Since genes predate present day political opinion and knowledge about Vitamin D there can be no specific genes for beliefs about these subjects. There can be and probably are genetic as well as epigenetic influences over.deep human character traits that would dispose one to one or the other belief. Traits such as our degree of empathy and courage, Deeper still our health and vitality.

    So unless I’m missing something, I could not take your cavalier stance to the obstructionism of the ACOG. I think they are terrible.
    Fred Glass

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