Evidence suggests that the vitamin D requirements of humans have been vastly underestimated. Current recommended intakes are based largely on invalid science, and increasingly diseases other than the traditional bone deformities of osteomalacia and rickets are being associated with intakes previously considered adequate. Autoimmune diseases such as type I diabetes, rheumatoid arthritis, multiple sclerosis and Crohns disease are now known to show inverse associations with sun exposure and vitamin D intakes, suggesting a role for vitamin D in the regulation of immunity. Because the levels of vitamin D intake now thought to be required to maintain adequate plasma levels are above the level that can be attained from food during winter months at high latitudes, researchers are interested in the fortification of foods. In the 1930s, fortification of dairy products was the likely cause of the reduction in cases of rickets in children.
In order to effectively fortify foods with vitamins it is essential that there is efficient absorption and delivery to cells and tissues. Because of this, researchers1 have investigated the bioavailability of vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol) from orange juice, compared to that from oral supplements. In a randomised, placebo controlled study, 105 subjects (18 to 75y) were fed 1000IU of vitamin D3, 1000IU of vitamin D2 or a placebo in either a supplement or fortified orange juice for a total of 11 weeks at the end of the winter. In order to assess vitamin D status, the researchers used the common vitamin D marker, 25-hydroxyvitamin D [25(OH)D]. The results showed that there was no significant difference in the serum levels of vitamin D3 between those subjects receiving the orange juice or the supplements. Likewise, there was no difference in plasma 25(OH)D levels between those receiving the vitamin D2 in supplements or orange juice.
These results suggest that fortification of orange juice is an effective way to increase plasma levels of vitamin D. At baseline, 64% of the subjects had 25(OH)D levels of less than 20 ng/mL, which would make them vitamin D deficient. This supports previous research that shows that during the winter months in higher latitudes, vitamin D insufficiency and deficiency become common. Those subjects in the placebo group actually had a decline in 25(OH)D levels (although it was not significant) suggesting that as the study progressed, their vitamin D status did not improve. Previous studies have shown that vitamin D3 is more effective at raising plasma levels of 25(OH)D that vitamin D2. However, in this study that data was not supported. The reason for this is not clear, but does suggest that in vitamin D insufficient populations, vitamin D2 is effective at raising plasma levels to healthier levels.