This is the most common question for vitamin D. Recommending, calculating or finding the right dose of vitamin D intake for anyone is difficult. That’s because it’s complicated!
Why? Because everyone is different. Different weights, genetics, skin colour, diets, UV exposure etc. What research has shown us is that the same D3 supplementation dose given to a group of people will result in a wide range of vitamin D blood levels as determined through 25(OH)D testing.
Here is a chart published by GrassrootsHealth which shows vitamin D levels by D3 supplementation dose taken. You can see that the same dose provides a huge variation in vitamin D blood levels. How can anyone really predict where you will fall in this chart?
Recently a new Canadian research paper1 was published in the peer reviewed journal Nutrients, by a group of researchers from the University of Alberta (Veuglers 2015). They used a dual approach and a review of 108 published estimates of vitamin D supplementation to determine the optimal vitamin D dose that minimizes the risk for both a low and high vitamin D blood level.
They found that a dose of 2909 IU per day is needed for 97.5% of Canadians to achieve the current blood level recommended by Health Canada of 50 nmol/L. They went further and determined that doses of 3094, 4450, and 7248 would be the doses required for normal weight, overweight and obese participants respectively. But they noted a problem. 2.5% of the people taking these doses would be predicted to have high 25(OH)D blood levels of over 200 nmol/L.
So they backed off on the dose numbers and reduced them to 1885, 2802 and 6235 for normal weight, overweight and obese participants respectively, to ensure that projected 25(OH)D levels would fall in a respectable range of between 58 and 171 nmol/L.
This study shows how difficult it is to recommend one dose of vitamin D for everyone. Their conclusion addresses the complexity of using a dose based strategy: “the large extent of variability in 25(OH)D concentrations makes a RDA for vitamin D neither desirable nor feasible.”
Where does that leave us? How do we answer the question on how much vitamin D to take? To effectively determine your ideal vitamin D intake or dose you will first need to determine what target 25(OH)D blood level you want to achieve. Remember that vitamin D intake can come from UVB exposure from sun exposure on bare skin (May – October, midday, UV index of 3 or higher, no sunscreen), artificial UVB exposure, foods or supplements. Many different organizations have published recommendations for 25(OH)D levels:
Health Canada - >50 nmol/L
Endocrine Society - >75 nmol/L
Osteoporosis Canada - >75 nmol/L
48 Vitamin D Scientists from GrassrootsHealth – 100-150 nmol/L
The Vitamin D Society follow the recommendations from the 48 scientists through GrassrootsHealth and their Scientists Call to D*action which recommends an optimal 25(OH)D level of between 100-150 nmol/L. This blood level is valid for all Canadians , all ages, weights, skin colour, and genetics.
The higher your target 25(OH)D level the more vitamin D intake you will require. Sun exposure in the summer can also significantly boost your vitamin D levels.
Weight is one of the key factors that affect individual vitamin D levels. Dr. Robert Heaney has a simple way to estimate your vitamin D intake. He recommends that people start off by taking 35 IU per pound per day or 75 IU per kilogram per day. Just multiply your weight by these factors to calculate your estimated vitamin D intake per day. To confirm that this intake is appropriate for you, have your 25(OH)D blood levels tested three months after starting this dose. If it is higher or lower than the 25(OH)D level you want to achieve, reduce or increase your intake respectively and re-test.
Keep in mind that the upper limit (UL) set by Health Canada and the Institute of Medicine for vitamin D intake is 4000 IU/d and the Endocrine Society UL is 10000 IU/d.
Finally, if all those calculations and numbers are just too much, you could start off by taking the average dose that Dr. Veuglers and his group found of 2909 IU/d which should put 97.5% of you over the 50 nmol/L recommended by Health Canada. That would be a great start!
Veuglers PJ, Pham TM and Ekwaru JP. Optimal Vitamin D Supplementation Doses that Minimize the Risk for Both Low and High Serum 25-Hydroxyvitamin D Concentrations in the General Population. Nutrients. 2015 Dec 4;7(12):10189-208. doi: 10.3390/nu7125527.