“How much vitamin D should I take?”

It’s probably the number one most common question I get today:

“How much vitamin D should I take?”

Like asking for investing advice, there are no shortage of people willing to provide answers, most of them plain wrong.

The media are quick to offer advice like “Take the recommended daily allowance of 400 units per day,” or “Some experts say that intake of vitamin D should be higher, as high as 2000 units per day.” Or “Be sure to get your 15 minutes of midday sun.”

Utter nonsense.

The Food and Nutrition Board of the Institute of Medicine has been struggling with this question, also. They have an impossible job: Draft broad pronouncements on requirements for various nutrients by recommending Recommended Daily Allowances (RDA) for all Americans. The Food and Nutrition Board has tried to factor in individual variation by breaking vitamin D requirements down by age and sex, but what amounts to a one-size-fits-nearly-all approach.

Much of the uncertainty over dosing stems from the fact that vitamin D should not be called a “vitamin.” Vitamins are nutrients obtained from foods. But, outside of oily fish, you'll find very little naturally-occurring vitamin D in food. (Even in fish, there is generally no more than 400 units per 4 oz. serving.) Sure, there’s 20 units in an egg yolk and you can activate the vitamin D in a shiitake mushroom by exposing it to ultraviolet radiation. Dairy products like milk (usually) contain vitamin D because the USDA mandates it. But food sources hardly help at all unless you’re an infant or small child.

It all makes sense when vitamin D is viewed as a hormone, a steroid hormone, not a vitamin. Vitamin-no, steroid hormone-D exerts potent effects in tiny quantities with hormone-like action in cells, including activation of nuclear receptors.

It is the only hormone that is meant to be activated by sun exposure of the skin, not obtained through diet. But the ability to activate D is lost by the majority of us by age 40 and even a dark tan is no assurance that sufficient skin prohormone D activation has taken place.

As with any other hormone, such as thyroid, parathyroid, or growth hormones, dose needs to be individualized.

Imagine you developed a severely low thyroid condition that resulted in 30 lbs of weight gain, lose your hair, legs swell, and heart disease explodes. Would you accept that you should take the same dose of thyroid hormone as every other man or woman your age, regardless of your body size, proportion of body fat, metabolism, genetics, race, dietary habits, and other factors that influence thyroid hormone levels? Of course you wouldn’t.

Then why would anyone insist that vitamin D be applied in a one-size-fits-all fashion? (There’s another world in which a one-size-fits-all approach to hormone replacement has been widely applied, that of female estrogen replacement. In conventional practice, there’s no effort to identify need, estrogen-progesterone interactions, nor assess the adequacy of dose, not to mention the perverse non-human preparation used.)

With thyroid hormone, ideal replacement dose of hormone ranges widely from one person to another. Some people require 25 mcg per day of T4; others require 800% greater doses. Many require T3, but not everybody.

Likewise, vitamin D requirements can range widely. I have used anywhere from 1000 units per day, all the way up to 16,000 units per day before desirable blood levels were achieved.

Vitamin D dose needs to be individualized. Factors that influence vitamin D need include body size and percent body fat (both of which increase need substantially); sex (males require, on average, 1000 units per day more than females); age (older need more); skin color (darker-skinned races require more, fairer-skinned races less); and other factors that remain ill-defined.

But these are “rules” often broken. My office experience with vitamin D now numbers nearly 1000 patients. The average female dose is 4000-5000 units per day, average male dose 6000 units per day to achieve a blood level of 60-70 ng/ml, though there are frequent exceptions. I’ve had 98 lb women who require 12,000 units, 300 lb men who require 1000 units, 21-year olds who require 10,000 units. (Of course, this is a Wisconsin experience. However, regional differences in dosing needs diminish as we age, since less and less vitamin D activation occurs.)

Let me reiterate: Steroid hormone-vitamin D dose needs to be individualized.

There’s only one way to individualize your need for vitamin D and thereby determine your dose: Measure a blood level.

Nobody can gauge your vitamin D need by looking at you, by your skin color, size, or other simple measurement like weight or body fat. A vitamin D blood level needs to be measured specifically-period.

Unfortunately, many people balk at this, claiming either that it’s too much bother or that their doctor refused to measure it.

I would rank normalizing steroid hormone-vitamin D as among the most important things you can do for your health. It should never be too much bother. And if your doctor refuses to at least discuss why he/she won’t measure it, then it’s time for a new doctor.

If you’re worried about adding to rising healthcare costs by adding yet another blood test, think of the money saved by sparing you from a future of cancer, heart disease, osteoporosis, diabetes, etc. The cost of a vitamin D blood test is relatively trivial (around $40-50, a fraction of the cost of a one month supply of a drug for diabetes.)

So how much vitamin D should you take? Enough to raise your blood level of 25-hydroxy vitamin D to normal. (We aim for a normal level of 60-70 ng/ml.)

Comments (17) -

  • Anne

    8/22/2008 6:58:00 PM |

    I'm so interested in the post ! I live in the UK where we don't get much sun, even in the summer. I'm in my mid 50s and am pale skinned and slim. Because I have osteoporosis and a heart valve defect I guessed I needed some vitamin D to help these conditions, and, after doing much research, started to take 4,000 ius of D3 per day last January. A blood test, four months later, at the beginning of May revealed that my blood level of 25-hydroxy vitamin D was 153 ng/ml (384 nmol/L), more than twice the 'normal level ! Certainly not the kind of level that 4,000 ius of D3 per day should produce ! I stopped taking the D3 and a couple of months later my 25-hydroxy vitamin D had dropped down to 64.8 ng/ml (162 nmol/L). My endocrinologist has now advised me to resume taking D3 but at 2,000 ius per day and I will have another blood test in two weeks time and then review the amount I should take based on those results. This shows how important it is to get tested !


  • Jenny

    8/22/2008 6:59:00 PM |

    If we do have known level from testing, do you have a formula or algorithm for calculating how much more we should add to raise blood levels of Vitamin D by a specific amount?

    I found one such formula in a book touting Vitamin D but the whole tone of the book was pretty snake-oil like and low on information for intelligent people so I did not have complete confidence in his tables.

  • auntulna

    8/22/2008 10:39:00 PM |

    You said "the ability to activate Vitamin D is lost by the majority of us by age 40".

    Did you mean to say it declines after age 40?

  • TedHutchinson

    8/23/2008 8:15:00 AM |

    Dr Cannel has some interesting points to make on the accuracy of some Vitamin D test results here.

    I am a 64yr old male living in the UK. My skin is fairly tanned as I try to get as much full body sun exposure as is available here however I have also been taking 5000iu/daily for a couple of years now. When I was last tested my score was 147.5nmol/l 59ng/ml. I wonder if Anne's numbers are the result of a faulty test.

  • Ricardo Carvaho

    8/23/2008 10:57:00 AM |

    where do we get enough vitamin D wihout worring about laboratory tests? What about the good old cod liver oil spoon some mothers used to give us when we were children? And what about getting of the sofa and start walking half an hour every day? I live in sunny Portugal. In the summer we eat a lot of sardines and other fish, and also spend hollidays in the beach. Instead of worring about things science or medicine may never understand, we could start looking back to our healthy paleolithic ancestors and ask what changes civilization has brought that made diabetic 7% of the total population. Excelent blog, Dr.!

  • Anne

    8/23/2008 2:39:00 PM |

    I am the other Anne. I will add GF to my name for "gluten free" so you can tell us apart.

    I think it important to stress that vitamin D supplementation needs to be continued long term. I have met too many people who have been prescribed 50,000 IU of D2 for 8-12 weeks and then told to stop because their 23(OH)D went over 30ng/ml. I know one person who's doctor stopped and started the D2 3 times.

    I agree that testing is important. I have had a difficult time raising my vitamin D to an optimal level. I am hoping my next test will be good. I have to wonder what role my low vitamin D played in my CAD.

  • Rich S

    8/23/2008 4:54:00 PM |

    Vitamin D dosage effects appear to be quite idiosyncratic.  I started out at a 25OH-vD level of 21 ng/ml, and currently have to take 10,000 IU (softgel) daily to keep my 25OH-vD level at 66 ng/ml.

    I'm male, and a big guy, plus T2 diabetic, so I probably need a larger dose.

    Take a look at the Vitamin D Council web site below. Search for the string "rule of thumb" in either of the links below, in which it is mentioned as a rule of thumb to increase 25OH-vD levels by 10 ng/ml would require 1000 IU vitD.

    -- or --

    BTW:  I bought your recently-published “Diabetes 101”  book (great job!). I want to give it to some of my poorly-managed diabetic friends, which tends to be most people, due to the poor level of diabetic care.

    I was a patient of Dr. Richard Bernstein, who I hear complimented your book.  He is quite a character, but taught me more about diabetes than all of my doctors forgot. I owe to him my current state of relatively good health in spite of diabetes.

  • Anonymous

    8/24/2008 12:46:00 AM |

    I personally went from 30ng to  60ng in 3 months by taking 8,000 ius of D per day.
    Any opinion from anyone on how often this blood level should be tested to regulate dosage?

  • TwinB

    8/24/2008 1:13:00 AM |

    Another interesting post, thank you. I'm wondering about your opinion on how often you think Vit. D levels should be tested after the initial test is done, especially if the levels are drastically low.

  • Jessica

    8/24/2008 4:04:00 PM |

    Excellent, excellent, excellent post.

    I, too, often get asked how much D someone should take.

    People tend to want to take it prior to checking (or in lieu of checking) blood levels. Often times, they're afraid to ask their doctor to order the test since many in our community have flat out refused to order it.

    My doctor says, "taking vitamin d without checking blood levels is like baking a cake without knowing the temperature of the oven."

    It's true. Without knowing your level, you don't know how much to take or for how long to take that dose.

    You may also need more at different times of year.

    I take 10,000 IU daily starting in mid November and continue until mid-May or so.

    I get my 25(OH) and serum calcium levels checked every 3 months.

    What drives me nuts is the media and other health professionals "warnings" against taking too much and/or their suggestion that you get more D through sunlight.

    Almost every article on D has some disclaimer from a medical professional warning against too much D. But, they fail to really communicate how RARE D toxicity is and how the risks of NOT taking enough D FAR outweigh the risks of taking too much D.

    And, to suggest that people get their D by spending time in the sun is irresponsible. As you know, the bodies ability to activate D from the sun decreases with age.

    We should be measuring levels and then managing levels through supplementation.

    Do you also check serum calcium levels?

  • Anne

    8/25/2008 2:50:00 PM |


    I get my serum calcium, serum inorganic phosphate and alkaline phosphatase measured at the same time as my 25(OH)D level. So far, even when my D was much too high, the levels of calcium and inorganic phosphate have been normal but the alkaline phosphtase was above normal. I think I'm lucky that my GP and endocrinologist will measure my levels judging from the problems other people have getting tested. My endocrinologist told me that he fully supports me having D3 supplementation so maybe that's why.


  • Dr. B G

    8/30/2008 3:40:00 PM |


    Don't forget to check Magnesium -- as we build stronger bones and drive mineralization there, Mag can get depleted from the blood and intracellular stores.

    Have you read the Magnesium report at TYP?


  • Dr. B G

    8/30/2008 3:40:00 PM |


    Don't forget to check Magnesium -- as we build stronger bones and drive mineralization there, Mag can get depleted from the blood and intracellular stores.

    Have you read the Magnesium report at TYP?


  • Anonymous

    2/3/2010 3:09:37 PM |

    Great book on this topic is The Vitamin D Cure.  It has a table that shows how much you individually need to take based on your weight and current level to reach your goal vitamin D amount...p49.  The average American needs 20 to 25 iu per pound to raise their level to 50 - 70.

  • mbarnes

    2/19/2010 7:01:45 PM |

    here is a good site on vitamin D, www.vitaminD3world.com The site also has links to a neat micro tablet form of vitamin D

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    11/4/2010 5:11:06 PM |

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