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At Harvard Forum, experts debate how much vitamin D is enough

Published: March 29, 2011
  • Author: Patrick J. Skerrett,


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Susan Reid
February 14, 2012

This issue has not even been on my radar screen, until I came back from a blood test today with a level of 8. I have been doing some reading and have read one source which says that the 50,000 unit/once a week treatment is D2, and that I really need D3. any thoughts on this. I’d rather be taking the right stuff, not a lot of the wrong stuff.

P.J. Skerrett
February 14, 2012

Susan — Low vitamin D is unfortunately all too common among Americans. There’s no consensus on D2 vs D3. UpToDate, an excellent reference for doctors, says “The two commonly available forms of vitamin D supplements are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). We suggest vitamin D3 when possible, rather than vitamin D2, because vitamin D3 is the naturally occurring form of the vitamin and it may raise vitamin D levels more effectively.” You can see the complete UpToDate article on vitamin D here:

February 04, 2012

Ive been taking 20,000 iu aday in the spring,winter time and drop down to 10,000iu in the summertime. Been doing this now for about 4 years. Not had any test done yet but feel fine.

rowenta toz torbası
December 28, 2011

The evidence for the health effects of vitamin D supplementation in the general population is inconsistent.

granite rockville
December 28, 2011

Vitamin D prevents rickets in children and osteomalacia in adults, and, together with calcium, helps to protect older adults from osteoporosis. Vitamin D also affects neuromuscular function, inflammation, and influences the action of many genes that regulate the proliferation, differentiation and apoptosis of cells.

Steve Powers
December 24, 2011

I am regularly outside installing security cameras for businesses and universities. I notice that when I am exposed to a large amount of sunlight and therefore Vitamin D, I feel better. Whether it is psychological or psyiological, the science proves it out. How much is too much is difficult to measure and should be measured with a good amount of research. Unfortunately, research will only yield the average amount of Vitamin D appropriate for the average adult. How do we give good advice for the other 50 percentile that is not average?

Steven Wright
October 18, 2011

Vitamin D is hugely important in my opinion for all types of health. Especially for immune system regulation. Anyone with an autoimmune disease really needs to get their Vitamin D levels checked regularly. As an IBS suffer I saw an immediate improvement in my health once I got my levels up above 50ng/dl. I run a blog about how I’ve been able to get my health back at

Kathy Silverstein
October 13, 2011

I took 50,000 IU of Vitamin d for about 2 months a year ago. My doctor had recommended it after finding I had low vitamin d levels. I tried to stick with it… but it didn’t seem to be changing or helping anything, so I stopped. There is some interesting research out there that shows that autism could be related to a lack of Vitamin d, especially in the mother before giving birth. There are studies of Somalis who moved to northern climates like Minnesota, and their kids started being diagnosed with autism at alarming rates. I have Asperegr’s so was interested in that theory, but who knows. [URL removed by moderator]
Another issue could be that I wasn’t absorbing the vitamin d properly due to possible malasorption issues. Either way, an interesting subject.

lizzy shafir
September 23, 2011

The thing is with all nutrients that toxicity causes nutrients to be used up and diminished. vitamin D also may be diminished from the toxiciy we are exposed to every day, therefore 400IU is probably not enough anymore.
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Jeff Davis
July 21, 2011

I read your article with interest and considered whether the production of cytokines in relation to vitamin D levels in the body has any bearing on any predispostion in an individual for osteoporosis?

samar mansour
May 26, 2011

dear sir..
i just want to ask a simple question and if there is a reply with an article attached i will be greatfull.
if i take a dose of 5000 iu twice per day,does the body absorbe more elemental vit d then a single dose of 1 tablet of 10000 the way the vit d 5000 iu that i have is in caplets not tablets.
thank you.

John Sparks
May 15, 2011

If everybody got their trainers on and went for a daily 20 min walk, our Vitamin D levels ought to be healthy-plus you are getting the added benefit of the exercise to boot.
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July 02, 2011

For those people living above the latitute of about Atlanta, GA,getting their trainers on most of the year will not work because they cannot absorb Vit D from the sun most of the months of the year. It will require a supplement for them. See: Vit D and Prevention of Chronic Diseases” (YouTube), video by one of top Vit D scientists (Boston) on behalf of Grassroots Health. Also, salmon is not a great source of Vit D unless it is WILD salmon, not farmed salmon. My experience was aching bones (osteomalacia) and deterioring teeth (leaching of calcium from bones and teeth to meet needs of vital organs) due to deficiency (16). Took 50,000 iu/wk for 8 wks, now take 4,000 iu to maintain level at about 55. To get to optimal level of 60-80, I ADD sun exposure of 25% of body during summer months for 15 min/day 3-4x week and am able to get my level up to 76. This also seems to be the only thing different to stop chronic UTIs (from 2007-Sep 2010). Remember what turns on our immunity? Vit D! Good luck!

April 03, 2011

A general comment; lots of nations don’t measure Vit D in IU but in micrograms. It would be really handy for international readers if you quoted quantities in both units.

Alex St Clair
April 02, 2011

The new research that “suggests” vitamin D plays roles other than calcium and phosphorous regulation includes hundreds of research studies as well as clinical reports and observations from numerous physicians.

But because our exposure to sunlight varies so widely, it’s hard to set an ideal vitamin D intake level that applies to everyone.

Best advice is to get yourself tested for vitamin D, then take enough vitamin D3 to maintain your 25(OH)D blood levels at between 50 and 65 ng/ml.

But for most people, the amount of vitamin D required is way more than the latest IOM recommendations.

For a list of diseases now associated with vitamin D deficiency, see

April 01, 2011

P S ( I live in florida and get quite a bit of sun)

April 01, 2011

My vit d level was tested by my Dr. after I fractured my Tibia. It was 14 – He said it should be 100. I have been taking 2,000 mg daily and it is still not higher.

March 31, 2011

“Being of sound mind and body, and responsible for my actions only, I also get my vitamin D the old-fashioned way. It’s a sunny afternoon, and I’m going out for a walk.”

Even getting it that way can be problematic. If you go for a walk, get sweaty, and decide to go home and take a hot shower, then you could negate all your vitamin D efforts. The substance your skin creates with sun exposure is…drum roll…on your skin! So if you take a hot, soapy shower, then you could be removing most of it before your body has a chance to absorb it.

Number one piece of advice: don’t listen to the IOM on daily intakes. Determine what the recommended blood level is, test for it, and correct your dosage accordingly.

Count Iblis
March 30, 2011

I take 10,000 IU per day in Winter and I then gradually reduce this to 5,000 IU per day in the Summer, such that on average I get a total of 10,000 IU per day from supplements and the Sun. I strongly believe that this is the right thing to do, because of the following.

If the UV index is above 3 or 4, you will get your maximum dose of around 10,000 IU of vitamin D quite fast. Dynamical equilibrium between vitamin D production and destruction will set in on a time scale of one hour or so. So, this means that the only way our ancestors would not get their maximum dose would be if the Sun didn’t rise above 20 to 30 degrees above the horizon, or if the weather was so bad that they would stay in their caves all day long.

Then, if we consider our ancestors, or for that matter animals living in Nature, and consider the conditions under which they systematically don’t get the maximum dose of vitamin D for a long period, you see that this corresponds to the season being late Fall, Winter, or early Spring. Obviously, it is then more difficult to find food. So, this suggests that vitamin D shortage is used by the body to regulate functions that use a lot of energy, like the immune system.

It makes sense to start to save energy in Fall when there is still plenty of food to find to prepare for Winter and falling Vitamin D levels are a good predictor that Winter is coming. Moreover, if you have a lot of fat reservers then you would have stored a lot of vitamin DS in your body, so your vitamin D levels would start to fall later in the season. Obviously, if you have more fat, you can postpone saving energy.

So, my idea is that animals in the wild use vitamin D levels to implement an optimal strategy to survive the Winter: accept a higher risk of diseases by letting the immune system function a lot more energy efficiently and gain more fat reserves as a result.

Then, we can also understand why the body uses vitamin D to switch on the synthesis of certain enzymes that are used to get calcium from our food. You can imagine that in late Winter when food supplies can be really low, you want to get as much energy from the meals that you eat. Now, getting calcium from food costs energy. Calcium is present in not so high concentrations in food so the entropy is quite high. So, just like dissolving a pinch of salt in aswimming pool and then extracting that pinch of salt from the water would involve spending some minimum amount of energy, getting calcium and other minerals from food is not free of charge.

In case of calcium, however, it is possible for the body to not get ot from food but from the bones instead. Because the concentration of calcium in the bones is much higher than in food, you save energy by getting it from the bones. Of course, this comes at the expense of maintaining the bones. However, if vitamin D levels are really low, that indicates that the Sun hasn’t been high in the sky for a very long time, which in turn implies that getting food from Nature would be very hard indeed. So, getting as much energy from whatever is still edible is the first priority. Maintaining the bones can be postponed.

So, this is my scientifically unproven belief in the role of vitamin D and that’s why I make sure I get 10,000 IU per day 🙂

Birgit Calhoun
March 30, 2011

I was tested after I had been taking 1000 IU of Vitamin D daily for at least 6 months and spending half an hour at noon getting sunshine on my legs and arms during the same time in the summer. My blood test showed that I had 14ng/ml of 25 (OH) D3. My doctor called that level very low. It took two 6-week courses of 50,000 IU/week and one course of 100,000 IU/week to get to the barely normal level of 32ng/ml. There are individual differences especially for those people who have malabsorption problems. The answer is: Get tested and go from there! Some investigators think that an optimal level of Vitamin D is above 60ng/ml. Optimal means optimal for all organ systems not just the bones. Just because a little bit of Vitamin D keeps children from having rickets doesn’t mean that that is optimal. It does not address the need for Vitamin D in all the other parts of the organism that have Vitamin D receptors.

William B. Grant
March 30, 2011

The Institute of Medicine committee was constrained by the Federal sponsors as to what types of evidence they could consider in their analysis. They could not use evidence for which sunlight was the source of vitamin D. As a result, they ignored the strongest evidence for many type of disease. Vitamin D experts such as Walter Willett and Beth Dawson-Hughes, who have reviewed the omitted evidence, conclude that it takes 1000-2000 IU/day or more to reach levels over 30 ng/ml associted with optimal health. There have been at least 28 letters, editorials, and papers published commenting that the IOM recommendations are inadequate.

March 30, 2011

The IOM took an known safe level of 10,000IU a day and added an extra safety factor. Toxicity seems to set in above 30,000IU a day for about 6 months for some people. Single doses of over 500,000IU are often given.

For supplement dose vs 25(OH)D levels see

Vitamin D Supplement Doses and Serum 25-Hydroxyvitamin
D in the Range Associated with Cancer Prevention, CF GARLAND, CB FRENCH, LL BAGGERLY and RP HEANEY, ANTICANCER RESEARCH 31: 617-622 (2011)

elizabeth nordhausen
March 29, 2011

Here in united arab emirates we constanty have to take blood tests to know if we are getting vitamin d. There is always a haze of dust which blocks the sunlight even on sunny days. I wish thhat dr’s and meteorologists could come up with a sunshine measurement to know how many rays are actually getting to us surely other places with smog and such have the same problem.

March 29, 2011

This topic seems to be all over the place. Is it possible to get an upper limit recommendation? It’s easy to say “get at least 600 IU”, but where does that end? When does it become toxic? Several people I know are taking well over 5000 IU daily. I have no idea if that is dangerous.

P.J. Skerrett
March 29, 2011

Larry — Good question. The IOM panel raised the safe upper limit for vitamin D intake to 4,000 IU for adults, and 1,000 to 3,000 IU per day in children depending on their age. If you want to dig down to the reference, here’s a link to the IOM report’s chapter on safety:

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