It turns out that vitamin D3 (cholecalciferol) has the edge.
In the U.S., vitamin D supplements are available over-the-counter as D3 (cholecalciferol; usually in 400–5000 IU doses) and by prescription as vitamin D2 (ergocalciferol; Drisdol and others; often prescribed at 50,000 IU doses).
In previous research, vitamin D3 supplements raised blood levels of vitamin D more than vitamin D2 did at equivalent doses. The blood test we use to measure vitamin D levels is the 25-hydroxyvitamin D blood level (25OHD)
Now two new studies, researchers reach the same conclusion.
In the first, a randomized trial, 64 older adults received daily D2 or D3 (1,600 IU) or monthly D2 or D3 (50,000 IU). Mean 25OHD levels were about 33 ng/mL at baseline. (NOTE: levels of 30-50 are considered sufficient by most experts).
At 1 year, mean 25OHD levels had increased by 9 ng/mL in both the daily and monthly D3 groups (to 41 ng/mL); while mean levels increased only by 6 and 4 ng/mL (to 39 ng/mL and 37 ng/mL) in the daily and monthly D2 groups, respectively.
So, the increase in vitamin D blood levels was greater with D3 than with D2, whether the vitamin D was taken daily or monthly.
However, in ALL cases, the 25OHD levels remained in the normal range!
In the second study, another randomized trial, 33 adults received 50,000 IU of vitamin D weekly, in either the D2 or D3 form; the average baseline 25OHD was about 28 ng/mL – in other words, these patients were vitamin D insufficient. Levels below 20 ng/mL indicate vitamin D deficiency.
After 12 weeks, increases in 25OHD levels were significantly greater with D3 than with D2 – as the increase from baseline was about 40 ng/mL with vitamin D3 (to a total vitamin D blood level of 68 ng/mL) versus only 22 ng/mL with the vitamin D2 (to a total vitamin D blood level of 50 ng/mL).
Note that in both cases, the 25OHD levels moved well into the normal range of 30—60 ng/mL.
In Journal Watch General Medicine, Allan S. Brett, MD, writes:
On average, oral supplemental vitamin D3 — the form made naturally after exposure to sunlight — raises 25OHD blood levels more than does vitamin D2.
The authors of the second study conclude, with good reason, that D3 is preferable for correcting vitamin D deficiency.
Note, however, that U.S. clinicians often give D2 by prescription to vitamin D–deficient patients: One reason might be the availability of high-dose D2 capsules that can be taken weekly or monthly; another might be a mistaken impression that prescription D2 is “stronger” than an equivalent dose of D3.
My interpretation of the data is a bit different. At lower doses (1000 – 2000 IU per day), I think the vitamin D3 is definitely the way to go. However, at higher doses (50,000 IU weekly or monthly), the vitamin D2 appears to be more than adequate—and it’s usually much less expensive.
So, here’s what I teach my residents and recommend to my patients:
If your vitamin D blood level (25OHD) is less than 30, you can choose either of the following: