In addition to having markedly lower potency, D2 also has a significantly shorter duration of action relative to vitamin D3. Both forms of vitamin D produce similar initial rises in serum 25OHD over the first 3 days, but 25OHD continues to rise with D3 supplementation, peaking at 14 days, and serum 25OHD falls rapidly in D2 treated subjects.
I would encourage people, especially people over the age of 65 to be tested for levels of vitamin D. When it comes to ranges for vitamin D, deficiency levels below 15 ng/ml and you should not have levels above 80 ng/dl. Many physicians are happy to have people at 20 to 30 ng/dl range. This is quite unsatisfactory and many people should be above 50 ng/dl.
Please also read the supplement section of this website for the University of Maryland and the vitamins, minerals, and supplements section of the University of Oregon website. Always check the warning section or the safety/toxicity information. Often there may be sections about conflicts with prescription medications. Read these very carefully. If you still have questions, have a talk with your pharmacist about what vitamins, minerals, and supplements to avoid when taking a prescription.