A recent study published in The Journal of Nutrition found that D2 administered in supplemental form or as part of a meal containing mushrooms increased blood levels of D2 but simultaneously decreased blood levels of D3.
Stephensen CB, Zerofsky M, Burnett DJ, Lin YP, Hammock BD, Hall LM, McHugh T. Ergocalciferol from mushrooms or supplements consumed with a standard meal increases 25-hydroxyergocalciferol but decreases 25-hydroxycholecalciferol in the serum of healthy adults. J Nutr. 2012 Jul;142(7):1246-52. Epub 2012 May 23.
This double-blind, randomized feeding trial sought to determine if consuming UV-treated mushrooms is an efficacious way to raise blood levels of D2 and total vitamin D [25(OH)D]. 38 participants were divided into four groups:
Each group received a lunch at the study site for six weeks that contained a serving of the mushroom they had been randomized to along with the corresponding capsule. They were provided with meals to take home for weekend lunches.
All the treatment groups experienced statistically significant elevations in D2 levels, but these gains were negated by an almost equal decrease in their D3 levels. Interestingly, the more vitamin D2 participants received, the more their D3 levels dropped. A significant negative association was calculated, such that for every .4 ng/mL increase in D2 levels, there was a .3 ng/mL decrease in D3 levels. At the end of the study, none of the treatment groups experienced statistically significant increases in total vitamin D [25(OH)D] status.
Similar studies conducted previously saw significant increases in total 25(OH)D status after D2 supplementation, but two key differences may explain this. Participants in the current study had higher baseline levels of total 25(OH)D ( >20 ng/mL) than other studies and presumably higher levels of D3 from sun exposure due to latitudinal and seasonal differences more favorable to vitamin D production.
The authors offered three possible explanations for the decreases seen in D3 levels as a result of D2 supplementation:
1. The first is the possibility that increased intake of D2 accelerates the breakdown of D3 by increasing the activity of the 24-hydroxylase, the enzyme responsible for the catabolism of D3. However, compounds involved in this breakdown were measured in this study and there were no significant elevations, meaning that there wasn’t increased activity.
2. Another possibility is that a negative reaction might occur between D2 and D3 in the liver, where increased D2 consumption could inhibit 25(OH)D production in general, so the body doesn’t more readily convert D3 into 25(OH)D.
3. Lastly, there could be competition between D2 and D3 for absorption in the gut, although unlikely since most D3 would have been from skin production in this study.
In conclusion, previous studies have shown increases in total 25(OH)D in deficient participants receiving D2 rich mushrooms, but these results were not replicated in participants with higher baseline levels of 25(OH)D. The concurrent decrease in D3 levels seen with an increase of D2 levels was such that no significant rise in total vitamin D serum was seen in any of the treatment groups. Due to unresolved concerns regarding the ability of D2 supplementation to favorably impact 25(OH)D status, supplemental D3 is still recommended at this time.