The Vitamin D testing sagas

Vitamin D testing is super complicated apparently. There are 2 forms one can measure-

1)      25-hydroxy Vitamin D: This is the less active form, and the normal range is around 30-100 ng/ml, and this is considered to be the far more reliable measure of vitamin D stores.

2)      1,25 dihydroxy Vitamin D: This is the exponentially more active form, but its levels are around a 1000-fold lower than the 25-hydroxy form, and the normal range is considered to be around 15-75 pg/ml. This one is considered less reliable because it has a short life (is degraded quickly) and its levels are regulated by calcium and other factors.

Remember I was freaking out about my ‘high’ D3 levels? It was the 1,25 dihydroxy form I was referring to.Below is a rundown of my supplementation and blood levels.

When I was taking 35000 IU/week (5000 IU every day for several months)

 25-hydroxy Vitamin D = 49 ng/ml (perfectly normal)

 1,25 dihydroxy Vitamin D = 86 pg/ml (ACK!)

Cut down to 15000 IU/week for 2 months

25-hydroxy Vitamin D = 49 ng/ml (perfectly normal and exactly the same as the last; my doc was rubbing his eyes in disbelief)

1,25 dihydroxy Vitamin D = 79 pg/ml (ACK! And  start to think that the lab test (from a small independent lab in Utah) may be effed up!)

Stop all vitamin D supplementation for 2 weeks . Decide to switch labs as I’m deeply suspicious of the 1,25 hydroxyvitamin D3 from the above testing lab. Go off to Labcorp, which is a big national chain.

25-hydroxy Vitamin D= 41 ng/ml (Falling- almost a 10 ng/ml drop in 2 weeks of no supplementation)

1,25 dihydroxy Vitamin D =11 pg/ml (Very different from the last value at 76 and in deficiency range)

Morals/Questions from this story:

1)Do not trust a small independent lab, you are much better off going to a large national chain, if you have the opportunity, for vitamin D testing. My endocrinologist is flummoxed as well- the perfect test to do is to actually send the same blood sample (or draw blood twice on the same day) to send to both labcorp and the lab in Utah to get to the bottom of this, but other than that, all we can conclude is that if one of the two tests is off, its logically more likely to be the first small testing lab, because labcorp is widely used and more validated, and most importantly, the values correlate with the amount of supplementation. I've observed this in the past, and  hence it was most disconcerting when the first testing lab reported those wonky 2nd test values. I hope this matter gets explored further, but I'm done with offering up my vein as the guinea pig.

2) Continuous Vitamin D supplementation is apparently necessary for some people, like me.  You cannot get much from diet and I seemingly get very little from sunlight ---normally I have no sun time, but during these past 2 weeks, I had 2  days (close to 8-10 hours) of sun exposure in Florida, with lots of skin bared, but sunblock applied. But my levels (of 1-25 and 25 forms) both dropped.  So unless I'm getting around 1-2 hours of sun with plenty of exposed skin (sunscreen free) on a daily basis, I would need supplementation. Had I continued to take no supplements, I project that, in around a month, I would have likely become deficient in the more stable  25-hydroxy form as well. 

3) But: taking too much may be less than optimal as well. I need to find that perfect balance.All of life and biology is about balance and this story is an excellent illustration of this. Right now, I’m going to go to around 12000 IU/week and see where that leaves me.