This is an estimate and is not a replacement for a lab test. We have made, and continue to make every effort to improve its accuracy. The best way to be sure you are in the range that you want to be in is to get tested regularly. When you get your results, you can enter them into the program and the app will of course use it in coming up with its own estimate. The reason we have this is that any given level assessment is only really valid for at most 90 days.

The main goals of developing an autopilot approach to level estimates were:

• to let users set the level to achieve rather than the dosage
• to allow people to pick their own source for a recommended level
• to provide a clear view of progress toward that goal

At the low end of the goal scale, we have 20. The RDA recommendation, which was receently changed to 600 IUs per day (800 if over the age of 70), was derived through study data as the amount that the average individual would need to achieve 20, which is considered sufficient. If you turn the dial to 20, the amount needed per day will in fact show 600 (if you are in the normal range for BMI).

In the middle of the range is the goal of getting to 40. The Vitamin D Council has an article about why their recommended levels, and how much D it takes to achieve them. Again, this is based on study data. If you spin the dial to 40, you will see the amount 3500. (Keep in mind, this is an all sources total, so if you think you are getting 500 per day from food, 3000 from all other sources.)

As is the case with many dose-related equations, Vitamin D exhibits properties of having diminishing returns. What this means is that as you take more of it, the amount that it will raise your level goes down. Finally, when you get to very high doses (10K per day), it drops by an order of magnitude. The ability to predict a level based on a daily dose is pretty straightforward. Mountains of study data underlie this. There are, however, things that can make it more complicated.

Body Mass Index [BMI]

Per above, because D is fat soluble, the amount of additional fat you have is a factor in a very simple way: some of what you make or ingest ends up being stored in your fat tissue. Which means it is not getting into your bloodstream (now).

The app applies the BMI factor in the following way:

• 25% BMI (overweight) -> 50% more D is needed
• 30% BMI (obese) -> 100%
• 40% or above -> 200%

It's important to note, as described above, this is applied to the dose. Let's look at an example case.

Suppose you have a BMI of 25 and you are getting 2000 IUs per day. The estimator will reduce the 2000 by 50%, which will yield 1000, which will put your estimate at 25. For a person with a BMI of 20, 2000 would yield an estimate of 30.

Drastic Changes in Dosage

When people use the application with a fixed dose for the full term (90 days), the estimate is extremely accurate.

Of course, it's quite common that people come to the app because they got a low test score and part of their plan to improve it is to increase their dosage. Consider a simple case: a User gets a test that comes back as 18 and after consulting his/her doctor decides to start takin 2000 IUs per day. We know that after 90 days of doing so we will see a stable level. However, if we intersect that ramp from deficiency to sufficiency, the question is will the estimate reflect the exact amount of progress that has been made so far in attaining the new level?

This was also part of the most recent work on the estimator: lab data has shown that first plateaus are achievable in three weeks after dosage changes. In some ways, this is just to say that doses that are more recent weigh more heavily on the estimate than ones that are remote. Dr. Holick conducted the studies that described the response curve.

Of course this means that if you get a low result and then take a large dose, the estimate will be more precise after this curve has been traversed.

The goal of the app is to prevent you from failling into deficiency. We believe strongly that the estimator will do that. That does not mean it is a replacement for a blood test. Get tested. Use the estimator to stay within the guard rails between your labs.

References

• Study data on BMI and D levels
• Lab tests vary by as much as 25% - even the gold standard is not an absolute.
• Vitamin D Council's Recommendation for Daily D Dose
• National Health Care source in UK says 90% of D 'must come from the sun'
• Landmark study on D levels: Doses Required to Achieve Various Levels - this has been shown in many studies, but very clearly laid out here: how much level rise you will get for each dose increase across the spectrum from small to large doses.