Food Contents and Biological Activity of 25-Hydroxyvitamin D: A Vitamin D Metabolite to Be Reckoned With?

Abstract

Only a limited number of foods naturally contain vitamin D such as fish, meat and offal, and eggs, and milk and dairy products. However, all these foods in addition contain the metabolite 25-hydroxyvitamin D (25OHD). From the few systematic studies which have been performed the food contents of 25OHD in animal foods are usually low but vary. Contents are typically very low in milk and fish (<0.1 µg/100 g), somewhat higher in meat and offal (0.2–0.4 µg/100 g) and up to 1 µg/100 g in egg yolk. It has been demonstrated that 25OHD is absorbed better and faster from the diet than native vitamin D and has metabolic effects of its own in regulating cell growth and calcium metabolism. Thus, the biological activity of 25OHD is greater than that of native vitamin D. However, there is as yet no consensus on the conversion factor that should be used for 25OHD to calculate vitamin D activity. Depending on the testing system used the factor varies from 1.5 to 5. If food contents and the higher potency of 25OHD are not included in dietary intake surveys, true vitamin D intake will be underestimated.

D Vitamini ve Kanserden Korunma

“…Yapılan çalışmalar cilt kanserinden korunmak için güvenli güneş ışığı miktarını henüz belirleyememiştir. Fakat güneş ışığına maruziyetin kısıtlı olması, özellikle güneş ışınlarının en dik açılarla geldiği öğle saatlerinde ve yaz aylarında dikkatli olunması gerekmektedir (1,5,6). …”

Vitamine D : sources, métabolisme et mécanismes d’action

“…Un paramètre largement sous-estimé dans le calcul des apports alimentaires en vitamine D est la contribution de la 25-hydroxyvitamine D, naturellement présente dans les aliments. En effet cette dernière n'est jamais prise en compte dans le calcul des apports exogènes de vitamine D. Pourtant ce métabolite est présent en quantité variable mais non né-gligeable dans un grand nombre d'aliments de consommation courante (Ovesen, et al, 2003 ;Schmid, et al, 2013 de cette molécule dans le maintient des taux plasmatiques notamment chez l'Homme n'est pas complètement établi (Ovesen, et al, 2003) et devra faire l'objet d'études approfondies, afin d'en tenir éventuellement compte dans les calculs d'apports vitaminiques. La principale source de vitamine D 3 est la synthèse endogène qui se déroule au niveau de l'épiderme, après une exposition aux rayonnements ultraviolets B (UVB) fournis par l'ensoleillement.…”

Are all steaks created equal?

“…The hypothesis behind these supplementations is that by increasing the calcium content in muscles post mortem, myofibril proteolysis could be faster. Although one does not know for sure if as a consequence of these experiments (which suggested some but variable success with respect to tenderness) such regimens are currently implemented by the cattle industry, they offer insight into levels of vitamin D 3 (8) . In nine publications from the same time period (not shown) levels in steaks between 0.2 and 25 ng/g fresh tissue are reported.…”