When you have a vitamin D blood test, the doctor orders a 25 hydroxy-vitamin D or 25(OH)D. As most reading know, the liver converts vitamin D into 25(OH)D, and thus a 25(OH)D blood test gives doctors a good reading of how much vitamin D you have and are getting. Most of the tissues all over your body then take this 25(OH)D and turn it into “activated vitamin D.”
This compound, 25(OH)D, used to be available in the USA as a prescription medication. This prescription would be advantageous, in theory, because you bypass the conversion in the liver, and are just giving the body straight what it wants: 25(OH)D. It is still made by some foreign drug manufacturers and is apparently still used in some countries, such as Switzerland where it is known as HyD.
How does HyD compare to vitamin D3? Is one stronger or more potent than another? That is, does one raise blood levels better than the other? Does one work better than the other in improving muscle strength, decreasing blood pressure, or improving immune function?
Professor Heike Bischoff-Ferrari and colleagues at the University Hospital in Zurich Switzerland decided to find out some of these questions. They tested the potency and effectiveness of 20 ug/day (800 IU) of vitamin D3 compared to 20 ug/day of HyD in 20 healthy postmenopausal women.
Bischoff-Ferrari HA, Dawson-Hughes B, Stöcklin E, Sidelnikov E, Willett WC, Orav EJ, Stähelin HB, Wolfram S, Jetter A, Schwager J, Henschkowski J, von Eckardstein A, Egli A. Oral supplementation with 25(OH)D(3) versus vitamin D(3) : effects on 25(OH)D levels, lower extremity function, blood pressure and markers of innate immunity. J Bone Miner Res. 2011 Oct 25. doi: 10.1002/jbmr.551.
First they found HyD [25(OH)D] is much more potent than vitamin D. That is, it looks as if it will take at least five times more vitamin D than HyD to raise blood 25(OH)D levels the same amount. And they found that HyD gets 25(OH)D blood levels up much faster, although at these amounts, both vitamin D and HyD appear to take about 3 months to have a full effect on blood 25(OH)D levels. At three months, the mean result of 20 ug/day of D3 was 30 ng/ml while 20 ug/day of HyD resulted in mean levels of about 65 ng/ml.
They also answered some of the other questions, on blood pressure, muscle function and immunity. What they found is that the 20 ug/day of HyD improved blood pressure, lower extremity function, and measures of immunity more than 20 ug/day of vitamin D3 did and did so significantly, despite the small sample size of ten women in each group. I think it’s important to note, that this is extremely likely due to the HyD achieving higher levels in their patients. The question that needs to be answered now is, what works better, 65 ng/ml using HyD or 65 ng/ml using plain vitamin D3? Here, HyD saw better results because the vitamin D group only achieved levels of 30 ng/ml.
The authors state,
“As we did not test an equivalent dose of HyD and vitamin D with respect to 25(OH)D level increase, benefits documented by HyD may likely be caused by its rapid increase in 25(OH)D level and higher achieved 25(OH)D compared to the dose of vitamin D3 tested. Alternatively, HyD may have additional benefits superior to vitamin D3, which will need further investigation.”
I remember Professor Robert Heaney of Creighton University telling me how much he liked to use 25(OH)D when it was available in this country as a medication. He thought it just worked faster than D3 does. However, the most likely reason 25(OH)D3 (HyD) was better than D3 in the above trial was that the potency of 25(OH)D3 is so much higher and that the same beneficial effect on blood pressure, muscle strength, and immunity will be observed with vitamin D3 if proper doses (5,000 IU/day) of vitamin D3 are used.