Vitamin D3 and High Serum Calcium

At my last Mayo Clinic visit, serum calcium tested at an all-time high, 10.5 mg/dL. The reference range is 8.9 to 10.1 mg/dL, so it's significantly above normal. Why is that? (1) It could be the myeloma attacking a bone somewhere; or (2) Dr LH noticed that I take a lot of Vitamin D3 and Vitamin K2 supplements, and decided to measure INR and Vitamin D levels. INR was OK.

Vitamin D levels came back the next day, and a couple of days after that Dr LH called to discuss them:

Test Name	Result		Units
25-Hydroxy D2	<4.0		ng/mL
25-Hydroxy D3	71		ng/mL
25-Hydroxy Total	71		ng/mL	Total (D2+D3) optimum level is 25-80 ng/mL

Dr LH pointed out that the Total Vitamin D is near the high end of the optimum range, and suggested that I cut my Vitamin D3 from 5000 units per day to 2500 per day, which is easy enough to do. Arguments for doing that (these are from my own research):

• Some authorities believe that it is possible for continuously-high levels of Vitamin D to cause high serum calcium.
• In some individuals, high levels of calcium can result in deposition of calcium in arteries, atherosclerosis.
• There is really not enough research to determine the safe amount of supplementation.

Arguments against reducing Vitamin D supplementation:

• According to the Vitamin D Council, toxicity begins at about 200 ng/mL and higher. They suggest an upper limit of 100. Other authorities seem to agree, though research on humans is lacking and individual responses could vary widely.
• The purpose of the high Vitamin D3 intake, along with Vitamin K2, is to combat bone loss. In a one-year test this seemed to be effective, with two density scans a year apart showing no measurable difference in density. It's just one short test, but I'm reluctant to make a change that might reduce the effectiveness of this treatment.

So what to do? My serum calcium levels have varied widely in recent months. Below is a chart of recent measurements.

Possibilities: cut the Vitamin D3 supplement in half or leave it the same for the current cycle, and, either way, the serum calcium might stay high or it might go down. But if I cut the D3 in half and calcium remains high, then we should worry about a myeloma hot spot in a bone somewhere. That's the worst case scenario here, so let's check for it.