Vitamin D-deficient rats fed bread made with vitamin D2-rich yeast experienced the same improvements in bone mineral content and bone mineral density as rats fed bread formulated with vitamin D3, according to findings published in the Journal of Agricultural and Food Chemistry.
On the other hand, blood levels of animals fed D3 were higher than the D2-fed animals, report researchers from Purdue University and North Dakota State University.
“Vitamin D-rich foods currently available in the market are not sufficient for most Americans to meet their daily vitamin D requirements,” wrote the researchers, led by Purdue’s Connie Weaver.
“We have demonstrated here that consumption of vitaminD2-rich yeast incorporated into bread results in increased plasma 25OHD status and improved bone quality in growing, vitamin D-deficient rats. This suggests that bread vitamin D made with high vitamin D yeast could be a valuable new source of vitamin D in the diet.
“Because vitamin D2 is naturally produced by yeast in response to UV light, this bread represents a novel, naturally rich food source of vitamin D,” they added.
The vitamin D2-rich yeast used in the study was supplied by Lallemand/American Yeast and the study was supported by the company.
Data on D
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.
One such option is bread, being a staple of many cultures, and according to the results of the new animal study, vitamin D2-rich yeast is bioavailable from bread.
Study details
The researchers investigated the efficacy and bioavailability of vitamin D in an 8 week dose-response study. Bread was made using either vitamin D2-rich yeast (Lallemand Yeast) or vitamin D3. Growing, vitamin D-deficient rats were fed diets formulated to contain 25, 100, 200, or 1000 IU crystalline vitamin D3 or vitamin D2 from D2-rich yeast baked into bread per kilogram diet. A total of eight experimental diets were studied.
Results showed, while both forms of vitamin D increased 25(OH)D levels in the animals, vitamin D3 increased levels to a greater extent than vitamin D2-fed rats.
In terms of bone strength, however, there were no significant differences between animals fd D2 or D3 bread. “Between rats fed the lowest and highest doses of vitamin D2 yeast, there was a 12.5 percent increase in trabecular BMC, a 23.1 percent increase in trabecular BMD, and an 8.8 percent increase in trabecular area,” wrote the researchers. “Between rats fed the lowest and highest doses of vitamin D3, there was a 1.3 percent increase in trabecular BMC, an 8.0 percent increase in trabecular BMD, and a 6.1 percent increase in trabecular area.”
D2 versus D3
There is some debate as to whether vitamin D3 is superior to vitamin D2 for raising blood levels of the sunshine vitamin. Indeed, scientists at Creighton University in Nebraska recently found that vitamin D3 may be 87 percent more potent at raising blood levels of the vitamin than vitamin D2, according to results published in Journal of Clinical Endocrinology & Metabolism.
Commenting on the differences between the types of vitamins, the researchers of the new study add: “We found that rats fed vitamin D2 for eight weeks had lower plasma 25(OH)Dlevels than rats fed vitamin D3, suggesting that in growing rats, vitamin D2 may have a lower capacity to increase and sustain plasma 25OHD levels than vitamin D3.”
Source: Journal of Agricultural and Food Chemistry
2011, Volume 59, Pages 2341-2346, doi: 10.1021/jf104679c
“Bioavailability and Efficacy of Vitamin D2 from UV-Irradiated Yeast in Growing, Vitamin D-Deficient Rats”
Authors: E.E. Hohman, B.R. Martin, P.J. Lachcik, D.T. Gordon, J.C. Fleet, C.M. Weaver