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Evidence that vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does vitamin D2. Trang HM, Cole DE, Rubin LA, Pierratos A, Siu S, Vieth R. Am J Clin Nutr. 1998 Oct;68(4):854-8. PMID: 9771862 Although the 1.7-times greater efficacy for vitamin D3 shown here may seem small, it is more than what others have shown for 25(OH)D increases when comparing 2-fold differences in vitamin D3 dose. The assumption that vitamins D2 and D3 have equal nutritional value is probably wrong and should be reconsidered.

Hypovitaminosis D in medical inpatients. Thomas MK, Lloyd-Jones DM, Thadhani RI, Shaw AC, Deraska DJ, Kitch BT, Vamvakas EC, Dick IM, Prince RL, Finkelstein JS. N Engl J Med. 1998 Mar 19;338(12):777-83. PMID: 9504937 Conclusions Hypovitaminosis D is common in general medical inpatients, including those with vitamin D intakes exceeding the recommended daily amount and those without apparent risk factors for vitamin D deficiency.

Vitamin D replacement in Asians with diabetes may increase insulin resistance. Taylor AV, Wise PH. Postgrad Med J. 1998 Jun;74(872):365-6. PMID: 9799895 We report three cases of vitamin D replacement in British Asians with vitamin D deficiency and non-insulin-dependent diabetes mellitus. In all cases, replacement resulted in an increase in insulin resistance and a deterioration of glycaemic control

Why would vitamin D be prescribed when vitamin D3 is available over-the-counter? Let's review the known differences between vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol): --D3 is the human form; D2 is the non-human form found in plants. --Dose for dose, D3 is more effective at raising blood levels of 25-hydroxy vitamin D than D2. It requires roughly twice to 250% of the dose of D2 to match that of D3 (Trang H et al 1998). --D2 blood levels don't yield long-term sustained levels of 25-hydroxy vitamin D as does D3. When examined as a 28-day area under the curve (AUC--a superior measure of biologic exposure), D3 yields better than a 300% increased potency compared to D2. This means that it requires around 50,000 units D2 to match the effects of 15,000 units D3 (Armas LA et al 2004). --D2 has lower binding affinity for vitamin D-binding protein, compared to D3 --Mitochondrial vitamin D 25-hydroxylase converts D3 to the 25-hydroxylated form five times more rapidly than D2. --As we age, the ability to metabolize D2 is dramatically reduced, while D3 is not subject to this phenomenon

Vitamin D and its major metabolites: serum levels after graded oral dosing in healthy men. Barger-Lux MJ, Heaney RP, Dowell S, Chen TC, Holick MF. Osteoporos Int. 1998;8(3):222-30. PMID: 9797906

A few researchers are turning their attention to the sunshine vitamin as a culprit, prompted by the experience of immigrants that have moved from their equatorial country to two northern latitude locations As evidence of widespread vitamin D deficiency grows, some scientists are wondering whether the sunshine vitamin-once only considered important in bone health-may actually play a role in one of neurology's most vexing conditions: autism. The idea, although not yet tested or widely held, comes out of preliminary studies in Sweden and Minnesota. Last summer, Swedish researchers published a study in Developmental Medicine and Child Neurology that found the prevalence of autism and related disorders was three to four times higher among Somali immigrants than non-Somalis in Stockholm. The study reviewed the records of 2,437 children, born between 1988 and 1998 in Stockholm, in response to parents and teachers who had raised concerns about whether children with a Somali background were overrepresented in the total group of children with autism

Barger-Lux MJ, Heaney RP, Dowell S, Chen TC, Holick MF. Vitamin D and its major metabolites: serum levels after graded oral dosing in healthy men.Osteoporos Int. 1998;8(3):222-30.PMID: 9797906 [PubMed - indexed for MEDLINE]