What's the Desired level?
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When Vitamin D is produced in the skin or taken as a supplement, it is changed by the liver to another form of Vitamin D called calcidiol.
The calcidiol (25-hydroxy-vitamin D) test is the common method of measuring Vitamin D in the blood.
The merck manual says 25-40 ng/mL is a normal level of calcidiol
today, commonly accepted levels are 32-45ng/mL.
Most Vitamin D research scientists suggest a higher level and believe 50-55 ng/mL is optimum
In sunny equatorial countries or a lifeguard with bare skin levels of 54-90ng/mL are not uncommon.
Researchers suggest the toxic level is above 150ng/mL
The landmark 1999 study by Dr. Reinhold Vieth found
1000iu/day of vitamin D3 had levels of 24ng/mL (60nmol/L after 3 months
2000iu/day of D3 had levels of 32ng/mL after 3 months
Dr. Vieth believes the safe upper limit which is now 2000iu/day should be increased to 10,000iu/day.
Over a period of 3 months,
every additional 40iu of D3/day raises calcidiol levels in the blood .28 ng/mL...so an additional 1000iu/day Vitamin D supplement is equal to raising your calcidiol level 7ng/mL.
Some, such as cardiac surgeon Dr. Donald Miller M.D. believes the daily dose should be higher. This is an interesting view from a heart surgeon. He claims in order to enjoy optimal health, we should maintain a vitamin D blood level of ≥50–99 ng/ml. Without sun exposure, to reach a level of 50 ng/ml requires taking a 5,000 IU/day vitamin D supplement.
I would look at 40--55ng/mL of calcidiol as being a good number. This may require daily doses in the summer of 1200-2000iu(37-50mcg) and in the winter 2000-4000iu/day (75-100mcg/day)
If possible a calcidiol blood test would give you a baseline and according to Dr.Vieth, each additional supplement of 1000iu (25mcg) would raise blood levels 7ng/mL over 3 months. It's something to talk to your doctor about.
