Vitamin D3 ist ungleich Vitamin D2

Zusammenfassung des Problems (von Dr. med. Giovanni Ruffo)
Früher galten die Vitamine D2 und D3 als äquivalent. Vitamin D2 ist pflanzlichen Ursprungs (Pilze, UV-B bestrahlte Nahrungsmittel), Vit D3 jedoch ist tierischer Herkunft (Synthese über die Haut und UV-B Licht, vom Plankton mit UV-B synthetisiert und den fetten Meeresfischen einverleibt (Lebertran!)). In den USA wird Ergocalciferol traditionellerweise der Nahrung beigemengt. Über Jahrzehnte wurde die Irrmeinung der Gleichwertigkeit verteidigt. Es zeigt sich aber, dass die klinische Wirksamkeit beim Menschen um das 2-3fache schwächer ist, gegenüber dem tierischen Konkurrenten Cholecalciferol. Dies wird bezüglich des Vitamin D3 mit den Unterschieden des Metabolismus, schwächerer Bindung an das Trägerprotein /DBP), schwächeren Produktion der Speicherform 25(OH)D in der Leber und mit dem schnelleren Abbau erklärt. Auf jeden Fall ist die Halbwertszeit von Vitamin D2 um die 14 Tage, diejenige von Vitamin D3 um die 60 Tage. Es gibt deshalb auch in den USA viele Befürworter, gänzlich auf das Vitamin D3 als Nahrungsersatz umzustellen.

The case against ergocalciferol (vitamin D 2 ) as a vitamin
supplement 1,2

Lisa A Houghton and Reinhold Vieth

ABSTRACT
Supplemental vitamin D is available in 2 distinct forms: ergocalcif-
erol (vitamin D 2 ) and cholecalciferol (vitamin D 3 ). Pharmacopoeias
have officially regarded these 2 forms as equivalent and interchange-
able, yet this presumption of equivalence is based on studies of
rickets prevention in infants conducted 70 y ago. The emergence of
25-hydroxyvitamin D as a measure of vitamin D status provides an
objective, quantitative measure of the biological response to vitamin
D administration. As a result, vitamin D 3 has proven to be the more
potent form of vitamin D in all primate species, including humans.
Despite an emerging body of evidence suggesting several plausible
explanations for the greater bioefficacy of vitamin D 3 , the form of
vitamin D used in major preparations of prescriptions in North
America is vitamin D 2 . The case that vitamin D 2 should no longer be
considered equivalent to vitamin D 3 is based on differences in their
efficacy at raising serum 25-hydroxyvitamin D, diminished binding
of vitamin D 2 metabolites to vitamin D binding protein in plasma,
and a nonphysiologic metabolism and shorter shelf life of vitamin
D 2 . Vitamin D 2 , or ergocalciferol, should not be regarded as a nu-
trient suitable for supplementation or fortification.      
Am J Clin Nutr 2006;84:694–7.
KEY WORDS      Vitamin D 2 , vitamin D 3 , ergocalciferol, chole-
calciferol, vitamin supplement
Taken together, the most plausible explanations for the
greater bioefficacy of vitamin D 3 are conceivably due to the higher
affinities of vitamin D 3 and its metabolites than vitamin D 2 for
hepatic 25-hydroxylase, DBP, and VDR and because vitamin D 3 is
not directly metabolized to 24(OH)D as is vitamin D 2 .

CONCLUSION
Vitamin D 2 , if given in high enough doses, prevents infantile
rickets and is capable of healing adult osteomalacia. However,
the inefficiency of vitamin D 2 compared with vitamin D 3 , on a
per mole basis, at increasing 25(OH)D is now well documented,
and no successful clinical trials to date have shown that vitamin
D 2 prevents fractures (19–21, 47). Given the assumption that the
intake of any nutrient will deliver defined effects [ie, supplemen-
tation with vitamin D will lead to an increase in 25(OH)D or
fracture prevention], it is clear that vitamin D 2 does not fit this
current nutritional notion. This is not to suggest that vitamin D 2
is not efficacious, but, because the units of the 2 forms is clearly
not equivalent, likely due to its distinct metabolic features and
diminished binding of vitamin D 2 metabolites to DBP in plasma,
continual application of vitamin D 2 in clinical use, including in
research trials, only serves to confound our understanding of
optimal vitamin D dosing recommendations. Furthermore, the
public expects to derive the equivalent effect per unit dose of
vitamin D, whether it is vitamin D 2 or vitamin D 3 . The scientific
community is aware that these molecules are not equivalent.
Therefore, vitamin D 2 should no longer be regarded as a nutrient
appropriate for supplementation or fortification of foods.