Kurt G. Harris MD

The PāNu approach to nutrition is grounded on clinical medicine and basic sciences disciplined by knowledge of evolutionary biology and paleoanthropology. The best evidence from multiple disciplines supports eating an animal-based diet high in fat, low in cereal grains and relatively low in carbohydrate.

Support PāNu

PāNu is ad-free, completely independent and has no outside sponsorship. If you value PāNu, now you can support it. Read this for more information.

In addition to buying from the book list, you can also support PāNu by making all of your Amazon purchases for any item through the Amazon Portal below

Amazon Portal

« Check out Nephropal | Main | H1N1, Vitamin D3 and Innate Immunity »

Vitamin D Home Testing

It is probably best to work with a cooperative local physician to have your (25) OH D3 level tested if you are supplementing. If your Doctor won't test you, or this is not an option for you, there are home testing kits available through several sources.

Reader Steve tells of an article in the New York Times regarding a large national laboratory that had some quality control problems relating to Vitamin D testing. Quest pharmaceutical had a number of erroneously high D measurements and had to do a "recall" of sorts, offering retests to to potentially affected patients.

From the Times article:

Some doctors who advocate vitamin D use said they had begun noticing some unusually high test results in 2007 and had begun complaining publicly in the summer of 2008.

Many laboratory tests, including Quest’s vitamin D test, do not require approval from the FDA.

"If you get your vitamin D level measured in the Mayo Clinic, the Cleveland Clinic and the Timbuktu Clinic, it would be nice if it came out the same value,” said Dr. Neil C. Binkley, associate professor of medicine at University of Wisconsin.

Dr. Binkley said that a few years ago he sent a sample of his blood to six laboratories and got results that ranged from 14 nanograms a milliliter, which would be a deficient level, to 41 nanograms — a level three times as high and considered adequate. While the tests’ consistency has improved since then, there can still be substantial variability, he said.

....the F.D.A. is considering increasing its role in regulating diagnostic tests. Now, test kits sold to labs, hospitals and doctor’s offices must be approved by the agency. But tests developed and offered by a single laboratory, like the Quest vitamin D test, do not.

That last paragraph is interesting. At the least, it seems there is little reason to assume that behemoth labs will necessarily be more reliable than those offering test kits. That might include the at-home test kits. 

The Vitamin D council is under direction of Dr. Cannell, who I have cited previously and who seems to be a pretty reliable character. The council has partnered with ZRT laboratories to offer a home test kit that is based on assessment of a spot of dried blood from a simple fingerstick. The test is a liquid chromatography/tandem mass spectrometry assay from the later reconstituted dried blood drop.

How accurate is it?

Analysis of (25) Oh D3 from dried blood spots vs serum.

Interassay coefficients of variation were 13%, 13%, 

and 11% at concentrations of 14, 26, and 81 ng/ml, respectively, for 25-hydroxy vitamin D3

The 25(OH)D3 assay was linear from 3.5 to 75 ng/ml (R > 0.99).

Blood spot and serum values showed excellent correlation for 25(OH)D3 (R = 0.91, n = 83). 

Maybe I have a reader who knows the inter-test variablility (precision) of serum LC measurements of (25) OH D3. This blood spot technique seems accurate enough to base your D replacement regime on, though, and in any case is more accurate than taking pills and just guessing.

The council offers the test kit, which you mail in, for a mere $65, or better yet, 4 tests for $220. They donate $10 of each test to the council for its non-profit promotion of Vitamin D health. It's a good deal at $65. ZRT charges $75 to consumers on their own web site.

If you live in New York State, you are out of luck. Patient empowerment is apparently illegal there. (Get ready for more of that with the coming "health care reform")

You can also go to grassrootshealth which is another good D advocacy site. There, if you agree to participate in a survey with them on D levels, the test is only $40.


Reader Comments (26)

"Patient empowerment is apparently illegal there. (Get ready for more of that with the coming "health care reform")"

Why is it illegal there, and why would there be more of it with the health care reform?

October 2, 2009 | Unregistered CommenterPotter


You'd have to ask the new York legislature why, but they don't allow out of state labs to sell home testing.

Would you expect there to be more freedom to control your own health decisions with increasing government regulation of the health care industry? At a minimum, they will force you to buy health insurance and eliminate your ability to associate with other individuals that choose healthier lifestyles. That is the very purpose of the mandate, to guarantee that low risk individuals will subsidize overweight grain-eaters.

October 2, 2009 | Registered CommenterKurt G. Harris MD

1; The whole D thing is interesting, had mine checked and was low. Thus engaged in conversation with cardiologist whose form letter instruction was inadequate (didn't specify 3 vs. 2) but net result has been encouraging dialogue with lots of docs about D that in the long run will be beneficial to many here.
2. Agree re less freedom. Ultimately the only way you can have mass coverage AND some level of cost control is by restricting utilization. The restrictions might be by default or design but are inevitable.

October 3, 2009 | Unregistered CommenterKen Smithmier

My husband and I are participating in the grassroots health study. Our initial D readings came in at around 50 - 60. This was in very early spring, and only about a month after we started supplementing with D, so our D should have been fairly low.

Surprisingly, our most recent results received about a week ago, were half that at 25 - 30. We have been supplementing and getting more sunshine in the summer months, but our D has decreased by half? One of the sets of readings most certainly was off, but which?

After this experience I would hesitate to estimate my D based on one test.

October 3, 2009 | Unregistered CommenterCourtney


I was unable to find a reference for the accuracy of the grassroots test - do you know which lab they use?

October 3, 2009 | Unregistered CommenterKurt G Harris MD

I participate in the grassrootshealth survey. The first test, six months ago, came in at 124. A couple of weeks later I had some tests done by my HMO that I wanted, and included a test for 25(OH)D, which came in at 85. I just got results from my second round with GRH and it came in at 104.

I typically take 6K IU per day, and got quite a bit of sun this summer.

October 3, 2009 | Unregistered CommenterRichard Nikoley

I recently read this - "Sunlight exposure creates reservoirs of vitamin D3 throughout the body that may be tapped during winter or when needed (that is, when calcidiol or 25(OH)D3 is low). Dietary vitamin D does not get distributed in this way." I don't recall you saying that on your Vitamin D posts. Do you agree with that statement?

I was going to pick up a vitamin D supplement this weekend, but after reading that and some of the comments on here about using a UV lamp, should I just opt for the lamp?

October 3, 2009 | Unregistered CommenterPotter


Vit. D can be stored only when blood levels exceed substrate starvation levels (meaning: supply is greater than demand). This level probably varies amongst individuals but the Vitamin D council mentions 50 ng/ml as a general threshold. Although intuitively it would seem to make sense that sunlight is better than supplementation, I've looked for but found no reports of differentiated effect based on the source of the D3.

Also there is considerable evidence that the SAD interferes with the skin's ability to create Vit. D. Sunlight or lamp exposure alone is not enough to guarantee your D levels: Testing is always necessary.


October 3, 2009 | Unregistered CommenterDavid

I wrote in the last blog (H1N1, Vitamin D3 and Innate Immunity) about my erratic and bizarre 25(OH)D results. They went from 154 ng/dl down to 60 ng/dl in four months, then up to 88 ng/dl, then up to 100 ng/dl and down again to 75 ng/dl in the space of 2 months. Several people told me it could be lab error and some people have recommended Grassrootshealth, but after reading Courtney's and Richard's results from Grassroots, they seem just as erratic as my lab's ! It's all very well to not to read too much into one result, but when several results are all over the place how to do know where we are ? 25(OH)D testing appears very inaccurate to me.

October 3, 2009 | Unregistered CommenterAnne

I'm also participating in the grassroots survery. My initial D3 test, when I'd only been supplementing with 5000IU daliy for a few weeks, came in at 46. I just sent off my second blood sample last week so will be curious to see what it shows now after 8 months of supplementation. I *hate* going out in the sun, have always hated it my entire life. Purgatory for me was when my family rented a house at the beach. I would go to the beach about 8 AM and stay for an hour or so, then come home and stay indoors and read until maybe about 4-5 PM, then I might be willing to go the beach again for a little while. But in mid-day forget it ? Still can't do it. If I have yard work to do I have to get it done well before 10 AM, otherwise it won't get done until the evening. So supplementation is probably a good thing for me (I also work in a windowless cubicle where I can go an entire day without knowing if it's sunny, rainy, snowy or whatever ourside.)

October 4, 2009 | Unregistered CommenterDebbie


Thanks for the info...so I guess it said people stored vitamin D from the sunlight because it would create so much of it, whereas from dietary sources perhaps they only did 1000-2000IUs, not a sufficient amount to exceed demand?

This was where I came across that info btw

Whatever the case, I'll go ahead and get a vitamin D supplement today after work.

October 5, 2009 | Unregistered CommenterPotter


The blog post (not an article) you referenced says:

"Sunlight exposure draws down the body's pool of cholesterol."

Hormonal amounts of cholesterol used are trivial relative to total cholesterol levels, and in any case this is no advantage at all unless you believe the diet/heart hypothesis.

"Sunlight exposure creates reservoirs of vitamin D3 throughout the body that may be tapped during winter or when needed (that is, when calcidiol or 25(OH)D3 is low). Dietary vitamin D does not get distributed in this way."

This is false. Both oral vitamin D and the UV-created D must be hydroxylated in the liver to make the circulating form of vitamin D, which is (25) OH D3 - this is the form that is stored in fat and liver and it is chemically the same whether derived from diet or sunlight.

"Much of the vitamin D3 manufactured in skin is deposited throughout the body in muscle and fat cells before it arrives in the liver. Much of the vitamin D3 absorbed from the digestive tract (food or pill) is delivered directly to the liver."

Again, they both go to the liver and the storage form is (25) OH D3.

"Absorption of vitamin D from diet is poor. Only about 50% of what we eat gets absorbed."

Irrelevant as long as you consume enough

"Vitamin D intakes "contribute only a negligible fraction" to blood stores compared to sun exposure."

Again, irrelevant as long as dose is adequate.

"Both vitamin D and many organic pollutants (e.g. pesticides) are fat soluble. As such, they reside in fat tissue."

So what?

I am open to the idea that there may be advantages to sun exposure over oral supplementation, but the only one I have proof for so far is that toxicity is less likely if all exposure is solely from the sun. Intuitively, the idea that UV might provide additional advantages (beyond vitamin D and tanning) is appealing to me, but I have not seen any convincing evidence of that yet.


I have seen that claim that Vitamin D storage "does not occur" until levels are at 50 ng/dl as well. That may be correct, but may be misleading. Serum (25) OH D should equilibrate with the storage depot - it may be true that when you dose orally, there is conversion in the liver to (25) OH and that when the serum level is transiently above 50 there is significantly greater net storage. I do not think this means that we do not store vitamin D until D levels are consistently at 50 ng/dl or above. Do you have a scientific reference for this?


Thanks for your input on your personal experiences with supplementation and testing.

I am doing some more reading on VItamin D pharmacokinetics and will post as I learn more.

October 6, 2009 | Unregistered CommenterKurt G. Harris MD

Thanks for all the good info Dr. Harris. I've been supplementing with a daily 4000 IU dose of Vitamin D for a few weeks. You've convinced me to get my levels tested instead of just blindly guessing how much I need to be taking, so I've ordered a test through the Vitamin D Council.

October 6, 2009 | Unregistered CommenterCavePainter

Wow thanks for the lengthy breakdown of that blog post I came across. Much appreciated.

October 7, 2009 | Unregistered CommenterPotter


You're welcome

October 7, 2009 | Unregistered CommenterKurt G. Harris MD


I picked up a vitamin D supplement a few days ago...I got Nature's Bounty D-5000 IU softgels made from soybean oil, gelatin, vegetable glycerin. I'll just take one of these a day, sound good? And I take the pill only when I eat, which is sporadically. Friday I took it around 3pm, Saturday at 10pm...should I try to take the pill around the same time each day? Or it doesn't really matter? I know you recommend up to 8,000IU, so I figure if I took the pill when I eat today(Sunday) at 2pm, it won't really matter that my last dose was just last night, nor will it matter in the future if its just 12 hours in between doses some days, especially since I get little sun these days.

October 11, 2009 | Unregistered CommenterPotter

I just got my result from Grassroots - 75ng. I'm now worried after reading posts describing wildly zig-zagging numbers on these tests. Won't be getting another test for 6 months. Pretty sure that my good test result (if it is accurate) comes from sun exposure and not from supplementation since I'd just started before the test. How high can I go with supplementation amount with a (supposed) 75 level? Don't want to overdo it.

October 11, 2009 | Unregistered CommenterBethany

Dear Dr Harris,

i just got my results back and my 25(OH)D was only 29,8 ng/ml! i bought some liquid D3, how much IU would you reccommend to take to get my levels up? would 5000 be enough or should i take 10000?


October 12, 2009 | Unregistered CommenterOliver

All -

My recommendations are in the original article:



depends on if you are still getting sun - if none, maybe 4000 iu/day and test again in 2 months


Not a fan of soybean oil - I prefer a vehicle of fish or coconut oil

October 12, 2009 | Registered CommenterKurt G. Harris MD

I am a Grassroots Health participant, as well. My first test (March 2009) gave a result of 71 after taking 4,000 IU a day for six months and getting some moderate UV exposure from a tanning bed. In spring and summer, I actually increased my oral intake of vitamin D to 10,000 IU a day and got generous amounts of sun exposure (but no artificial UV). Consequently, my second test (September 2009) indicated that I was at 144. I have knocked off a few thousand IUs and am curious what the result will be at the end of winter.

But now for something I found totally inexplicable....my teenage daughter's doctor recently tested her vitamin D level and although she had been supplementing with only 2,000 IU and getting very little sunlight, the result was 147. The doctor was not concerned and said that the results probably were due to a vitamin D supplement being taken shortly before my daughter's blood was drawn. Has anyone else heard that this is possible? Could this account for some of the varying results others are seeing?

Even with that high vitamin D level test result, my daughter still managed to get the flu last week. The doctor suspected it was H1N1 but her symptoms were too recent for an accurate test. My daughter is now fully recovered and I have to say that she had the mildest case of the flu I have ever seen in my life (which I, of course, attribute to vitamin D). This leads me to believe that even if vitamin D won't prevent the H1N1 flu in every case, it will reduce the severity of it.

October 22, 2009 | Unregistered CommenterJeff


Briefly, the answer is no -the pharmacokinetics of oral D administration cannot explain a level that high - the enzyme action converting D to 25 (OH) D - which is what is measured - is basically zero order at serum levels that high. So a large oral dose ( even 100K units) cannot boost your (25) OH D to those levels that quickly.

This will be the subject of my next post.

As far as your daughters flu experience - milder illness and less frequent infections are both observed with D supplementation.

October 22, 2009 | Unregistered CommenterKurt G. Harris MD

Thanks for the info, Dr. Harris. I am looking forward to reading your next post. So I guess only further testing is going to clarify my daughter's anomalous vitamin D test result.

You may be planning on covering this in but something I am curious about: Can intense sun exposure (such as someone would get on a vacation to the tropics) temporarily raise someone's vitamin D levels markedly? Others such as Richard Nikoley seem to have experienced this.

October 23, 2009 | Unregistered CommenterJeff


"So I guess only further testing is going to clarify my daughter's anomalous vitamin D test result."

It may not be anomalous as there is wide variability in dose response. It is not a dangerously high level in any case. At 300 mg/dl you can start to worry.

"Can intense sun exposure (such as someone would get on a vacation to the tropics) temporarily raise someone's vitamin D levels markedly?"

over one week? -yes but only by so much - you likely can't go, say, from 20 to 150 with only week of sun.

October 23, 2009 | Unregistered CommenterKurt G Harris MD

"It may not be anomalous as there is wide variability in dose response..."

Isn't that the truth! It boggles my mind that my daughter was apparently able to obtain with 2,000 IU per day and very little sun exposure a vitamin D level that I obtained only with 10,000 IU per day and regular sunbathing. Just goes to show that anyone who is trying to raise their vitamin D level without having it tested is just taking a shot in the dark.

Thanks again, Dr. Harris.

October 23, 2009 | Unregistered CommenterJeff


That's why I don't recommend a supplement level for adults over 4000 without testing.

October 23, 2009 | Unregistered CommenterKurt G Harris MD

There are online sites that allow me to order a variety of blood tests without my doctor's approval. I simply place an order for the blood test I want: wait for the lab test form to be e-mailed to me; and take that blood test form to a laboratory where the blood sample is taken. It takes 2 to 3 days to get the results back and the testing is performed by a certified lab.

December 22, 2009 | Unregistered CommenterEd
Comments for this entry have been disabled. Additional comments may not be added to this entry at this time.