pastafreak, emmie need not worry as to whether her GP has prescribed D2 or D3. They are both effective for straightforward Vitamin D deficiency and there are clinical indications for prescribing D2 in preference to D3 in some circumstances.
D2 is largely derived from plants, whereas D3 is mostly from animal origin - it's not the whole story but I don't want to overcomplicate the matter here. D2 has been the Vitamin D version of choice for vegans for very many years for obvious reasons and therapeutic doses can be just as effective when taken regularly as D3. Vitamin D3 is metabolised in the body via simpler metabolic pathways than D2 and it is the conventional treatment for the majority of patients. Nevertheless, the value of D2 should not be dismissed.
The British National Formulary, which can be regarded as the doctor's bible on drugs, continues to list D2 and D3 along with other analogues as prescribable. The BNF does not advise that D3 should be given preference over D2 and quite rightly so. The other analogues are available for patients with renal disease, some endocrine disorders and other disorders.
The one and only issue over D2/D3 prescribing in a patient with no other comorbidities other than strightforward deficiency is availability. D2 is more costly to manufacture and there is less of it around. Health food shops charge a great deal more for D2 than D3 and add to the issue by confining sourcing to exotic mushroom species etc.
Biochemists such as myself teach this stuff to medical students and my own staff lecture on vitamins in the university medical school. Believe me, there is a lot of misinformation on the internet regarding this issue of the preferred vitamin D analogue and a lot of it should be taken with a pinch of salt.
The vast majority of vitamin science is taught to medical students by
biochemists and my staff d