Summary of dosing suggestions

  • American Academy of Pediatrics recommends 400IU starting soon after birth and continuing through childhood and adolescence.

  • 1000IU per day is the minimum dose that can be expected to significantly raise an adults Vitamin D level and is the current recommendation of the Canadian Cancer Society.

  • 1000IU per day is considered conservative by experts in the field. Most experts suggest 2000 IU is appropriate and safe. (19) (for more on the safety of high dose Vitamin D click here)

  • For older, obese, dark skinned or people who get very little sunshine, 2000IU may be the appropriate dose. (19)

  • The Vitamin D council suggests taking 5,000 IU per day for three months, then obtain a 25-hydroxyvitamin D test. Adjust your dosage so that blood levels are between 50–80 ng/mL (or 125–200 nmol/L) year-round

  • Women who are pregnant or breast feeding should consider increasing their Vitamin D intake to 2000IU according to the Canadian Pediatric Society. (Press Release)

Is it worth having a vitamin D test before starting taking supplements? Most suggest not because almost everyone living in Northern areas are at least not at optimal levels and most are close to absolute deficiency.
Most suggest having the first test several months after starting supplementation to determine if your levels is high enough and then making dosing modifications.

Most importantly one needs to take the correct supplement. There are several form of vitamin D and the correct one to take is Vitamin D3, (colecalciferol). (1)

Ironically the only form of vitamin D available by prescription (in the USA and UK) is ergocalciferol (D2).  This is a synthetic form of vitamin D and is two to four times less effective than Vitamin D3 (colecalciferol) in raising your vitamin D levels. (9, 10) Also, not being a natural substance it is metabolized into metabolites that are not natural to the human body. (11)Vitamin D3 (Colecalciferol) is available over the counter in the USA and over the internet.

However beware that not all preparations of Vitamin D sold are pure vitamin D3. One of the commonest sources of vitamin D for commercial supplies is cod liver oil and this also contains high levels of Vitamin A. Vitamin A antagonizes and can effectively cancel out the effects of Vitamin D. Therefore products that contain both A and D should be avoided.  For the same reason cod liver oil should be avoided. (1)

The Canadian Cancer Society now recommends that all Canadians take at least 1000IU Vitamin D3 per day.  This recommendation is something of a turning point in medicine. It is the first time any official medical institution has recognized that a simple dietary supplement may influence the incidence of cancer.

However many studies have shown that 1000IU is far from ideal if one is to bring levels up to the optimal needed for cancer prevention. (1)

The upper limit proposed by the Institute of Medicine’s Food and Nutrition Board in the USA in 1977 is 2000IU per day. However even this is based on old and many believe old and inappropriate literature (17)

In one study 104 Vitamin D deficient Afro-American patients were treated with 2000IU for one year. At the end of the treatment period 40% had failed to reach a target level of 32ng/ml. (18)

In another study 4000IU given for at least six months managed to achieve levels of 44ng/ml (19)

Dr Heaney at the Creighton University Medical Center in Omaha Nebraska, one of the worlds leading authorities on vitamin D recommends that adults should take 5000IU per day to achieve optimal levels (19) This is also the suggestion of the vitamin D council in the US who state that if you regularly avoid sunlight exposure you may need as much as 5000IU per day.

Dr Cannell of the Vitamin D council in USA recommends 5000IU per day during the fall and winter, and 2000IU per day during the rest of the year.

You should consult with your physician and if possible have your vitamin D levels measured.


What Blood level of Vitamin D is Optimal?

People who work out of doors in sunny parts of the world have levels of vitamin D in the 50-70ng/ml range. Sunlight alone cannot produce toxic levels of vitamin D as the body starts to destroy the excess. It would therefore appear that nature/evolution has determined that 50-70ng/ml is the optimal level. (12)

Patients are classified as deficient when levels drop below 15ng/ml. (Some consider 20ng/ml to be the cut off) (1)

Multiple epidemiological studies have suggested that levels between 33-52ng/ml are necessary to achieve significant reductions in the incidence of the most common forms of cancer. (14, 15)

Finally Lappe’s cancer prevention study (see section on Cancer Prevention) showed that levels above 29-38ng/ml were associated with marked reductions in the incidence of cancer. (16)


The Safety of High Dose Vitamin D

The safety of high dose Vitamin D is still debated by some health authorities. However the literature demonstrates that such concerns are unfounded.

In the US the official position is that the upper limit of intake should be 2000IU. (144) In the UK the position is more conservative and stands at 1000IU per day.  (145,146) The recommendations came about by establishing the highest dose that appeared to have no adverse effects and dividing by four to ensure an adequate safety margin. (147)

Studies have clearly shown that doses of 10000IU/day are safe (19) and that literature report of toxicity only occur at doses of the order of 40,000IU per day.(158)

In a study in elderly nursing home patients 5000IU was added to bread and given the the patients every day. After 12 months, during which no adverse events were noted plasma levels increased from a mean of 11.4ng/ml to 50ng/ml and was over 29,6ng/ml in 92% of the patients. (153)

Multiple sclerosis patients where a very strong link between Vitamin D deficiency and the condition has been shown are often given doses of 6000IU per day and higher.

Until recently no one had conducted a formal phase I study to determine the safety even higher doses of Vitamin D.  In 2007 Vieth at al published a study in the American Journal of Clinical Nutrition showing the

Safety of doses up to 40,000IU per day to patients suffering from Multiple Sclerosis (MS). (143)

In this study 12 patients with MS were given weekly doses of Vitamin D3 and the dose escalated every few weeks. The table below shows the dosing regimen:

Study WeekDose of D3/IU/week
1-2        0
3-4     28000
5-10   56000
11-16 112000
17-22 224000
23-28 280000

The highest dose given equates to 40,000IU of Vitamin D3 per day. None of the patients developed hypercalcemia and no adverse events were seen in any patient throughout the 28 week trial. The mean serum Vitamin D levels at the start of the study was 31ngs/ml and at completion of the trial were 154ngs/ml.

While this publication showed the results of the first 28 weeks of therapy it has been reported that the study continued for twelve months and no adverse effects were seen. NO ONE SHOULD CONSIDER TAKING DOSES THIS HIGH UNLESS UNDER MEDICAL SUPERVISION. THESE RESULTS ARE PRESENTED HERE TO UPDATE YOU ON THE LATEST MEDICAL RESEARCH AND PERHAPS REASSURE THAT DOSES OF 1000-2000IU PER DAY ARE UNLIKELY TO PRODUCE ADVERSE EFFECTS.

The products and the claims made about specific products on this site have not been evaluated by the United States Food and Drug Administration and are not intended to diagnose, treat, cure or prevent disease. The information provided on this site is for informational purposes only and is not intended as a substitute for advice from your physician or other health care professional. You should consult with a healthcare professional before starting any diet, exercise or supplementation program, before taking any medication, or if you have or suspect you might have a health problem.



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