Dietary vitamin D is available in two forms. Ergocalciferol (vitamin D2) is the form of vitamin D found in plant tissues and cholecalciferol (vitamin D3) is the form found in animal tissues. Both are available as supplements, and ergocalciferol is the prescription form of the vitamin. However, there is evidence that the cholecalciferol is more biologically active than ergocalciferol, and this relates to the fact that it is cholecalciferol that is produced in our skin by the action of ultraviolet light and thus our biochemistry is more tuned to this form of the vitamin. In particular, cholecalciferol can bind more readily to the vitamin D transport protein, facilitating improved absorption rates and transport around the body. Cholecalciferol also requires a greater number of metabolic steps before deactivation, and thus may remain active in circulation for longer. However, ergocalciferol is effective at increasing plasma levels of the biologically accepted vitamin D marker 25-hydroxyvitamin D, and so should not be dismissed as ineffective.
For example, in a study investigating the effects of vitamin D on the plasma levels of 25-hydroxyvitamin D in young infants, researchers administered either ergocalciferol or cholecalciferol to breast fed one month olds to assess changes in the vitamin D status of the infants1. Both supplements were effective at improving the plasma levels of the infants after three months of receiving the supplements. A total of 23 infants were deficient in vitamin D at the baseline reading, but only 2 % were still deficient after the supplement period. The improvements in the plasma levels of 25-hydroxyvitamin D were not different between the two types of vitamin D suggesting that both ergocalciferol and cholecalciferol are effective at improving the vitamin D status of infants. However, while only 75 % of infants in the ergocalciferol group managed to attain the 50 nmol/L cutoff levels of 25-hydroxyvitamin D, in the cholecalciferol group this level was attained by 96 % of infants.
Dr Robert Barrington’s Nutritional Recommendation: These results support other studies to show that both forms of vitamin D are effective at raising plasma levels of 25-hydroxyvitamin D, but that cholecalciferol is more effective. Although no statistical significance was reached between the two groups the ergocalciferol fed infants did have lower levels of 25-hydroxyvitamin D (17.6 nmol/L) compared to the cholecalciferol fed infants (22.3 nmol/L). Therefore cholecalciferol remains the supplements of choice to improve vitamin D status.
RdB
