By Stephen Daniells, 10-May-2010
Fortification of orange juice with either vitamin D2 or D3 produces the same increases in blood levels as consuming either vitamin via capsules, says a new study.
Vitamin D in the D2 or D3 form is “equally bioavailable in orange juice and capsules”, according to a study led by Michael Holick from Boston University and funded by the US National Institutes of Health (NIH) and the Beverage Institute for Health & Wellness, a division of Coca-Cola North America.
Several studies have reported that vitamin D2 is between 30 and 50 per cent less effective as the D3 form in maintaining blood levels in humans.
The new study, published in the American Journal of Clinical Nutrition, could challenge this view however. Holick and his co-workers arrived at their conclusion after performing a randomized, placebo-controlled, double-blind study with over 100 health adults.
Vitamin D refers to two biologically inactive precursors – D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former is produced in the skin on exposure to UVB radiation (290 to 320 nm). The latter is derived from plants and only enters the body via the diet.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active ‘storage’ form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
According to Holick and his colleagues, vitamin D is already used to fortify orange juice, and is often added in combination with calcium. “[However,] it is unknown whether vitamin D is as bioavailable from orange juice as it is from supplements,” they said.