How much vitamin D should I take?
One of the most common questions we receive is how much vitamin D should I take to get my serum level to the desired range (40-60 ng/ml)? There is no simple answer, no magic bullet, as everyone's body is different. But here is the information you need, from our D*action data, to help you find a starting point to optimize your vitamin D level.
Recorded Supplementation vs. Serum Level
Using D*action data for 3667 participants, we plotted daily vitamin D supplementation (as reported in the questionnaire) vs. serum levels (as determined by our test). The main conclusion is that results from supplementation can vary greatly from person to person.
You may click on the graph to see a bigger view. The best-fit line (middle line) represents the average serum level (y-axis) for a particular vitamin D supplement amount (x-axis). The 25(OH)D value at zero supplement value on the x-axis (33 ng/ml) reflects vitamin D input from UVB exposure and food.
In a paper titled "Vitamin D Supplement Doses and Serum 25-Hydroxyvitamin D in the Range Associated with Cancer Prevention" two points were illustrated by this graph:
- The tendency for serum 25(OH)D to rise with increasing dosage is much more gradual at higher serum levels than at the lower levels.
- There is a very large spread of 25(OH)D values at each intake amount
Using this data, we added 95% probability bands (outer lines) that provide information regarding the doses required to ensure that 97.5% of the population would have 25(OH)D concentrations above a given level. In that graph, the lower band crosses 40 ng/ml at 9,600 IU/day, therefore, 9,600 IU/day is the supplemental intake that ensures that 97.5% of the population would reach 40 ng/ml. For the IOM, with a goal of 97.5% above 20 ng/ml, the amount of vitamin D (all sources) should be approximately 7000 IU/day.
How do I reach the optimal vitamin D blood level?
If there is no magic amount of supplement that will do the trick, then you have to test. The best way to begin is by doing a vitamin D test to find your baseline level - before you start taking any new supplements. Then, you use this chart to move your blood level to the desired range.
This chart is based on our data and assumes an adult of average size, 150 lbs. So if you are about that weight and your first test recorded 20 ng/ml with you taking 1000 IU/day but you want to move your blood level to 40 ng/ml, then you need an increase of 20 ng/ml. Reading the chart you see that you should increase your current supplementation by 2600 IU/day, making it a new total of 3600 IU/day. Again, the chart is based on averages and individual results vary - so after 3-6 months we recommend testing again to see if you have achieved the desired level.
What about toxicity?
This first graph shows that the rise in 25(OH)D with higher supplement intakes is very gradual and even with intakes well above 10K IU/day, very few people reach 200 ng/ml (the lower boundary for potential toxicity).
Average serum level using only sun exposure and diet
We do have a number of people in D*action who do not take any vitamin D supplements. That means that they get their vitamin D from sun exposure and food alone. There is a common belief that spending 15 minutes outside once a day with just your face and arms showing will provide adequate vitamin D. This is not what we have seen in our data. Instead, our data showed that while there are individuals at each time interval of sun exposure who will reach 40 ng/ml, the average level did not reach 40 ng/ml until a substantial amount of time was spent in the sun each day. This varies from person to person and many individual factors such as latitude, season, age and skin pigmentation affect how the sun's rays are metabolized through skin. However, since many of us cannot make that kind of time commitment to mid-day sun exposure, supplementation is the key for most of us to achieve optimal vitamin D status.