There is much controversy surrounding the optimum levels of Vitamin D3 supplementation, and while the currently established safe upper limit for Vitamin D3 is listed as 2000 IU per day for adults and children over the age of 12 months, many experts are now questioning this level and calling for the upper limit to be increased to levels as high as 10,000 IU:
- Vitamin D and Cancer Mini-Symposium: The Risk of Additional Vitamin D
Another method to obtain adequate levels of Vitamin D3 is through approximately 15-20 minutes of near full body exposure to the sun at peak sun times during the summer. In this amount of time at peak sun during peak sun months, our skin produces between 10,000 and 20,000 IU of Vitamin D3. No additional Vitamin D3 is produced in longer exposure, and peak levels are produced prior to any sunburn pinkness.
However, the time of the day, the season of the year, and the latitude you live in alter the the amount of UVB rays (the Vitamin D3 producing rays) you are exposed to as the following study from India points out:
Even at high noon, UVB exposure varies so much by season, that you may have trouble getting enough Vitamin D3 in the near winter and winter months depending on your latitude as the diagrams of UVB exposure in various US cities by month in the following article show:
Vitamin D3 supplementation may be contraindicated in certain diseases including sarcoidosis, so please talk to your doctor before taking high level supplements of Vitamin D3.
Some great articles related to dosing and testing for Vitamin D3 include:
Note the discussion on the prescription form of Vit D (Vit D2) and the resulting unnatural metabolic by-products in the 2nd to last paragraph on page 13. Here's the article that the above article refers to in support of Vit D3 over Vit D2:
There are multiple test methods for measuring 25(OH)D levels. The DiaSorin RIA method is the standard that has been used in most research studies so it is important to get tested via a lab that uses a testing method that returns results that are well calibrated to the DiaSorin RIA standard so results can be compared equally with the results found in these studies:
- Comparison of Commercially Available 125I-based RIA Methods for the Determination of Circulating 25-Hydroxyvitamin D
This article, from ZRT Laboratory, has some additional information on the differences in the three most common testing methods for 25(OH)D:
Relatively inexpensive home self tests for Vitamin D levels - 25(OH)D tests - are available from the following links, and these tests apparently are endorsed by many of the experts in the field of Vitamin D:
And members of CpnHelp have been posting and tracking their 25(OH)D levels on the following thread: