Very poor bioavailability of vitamin D2 from bread made with UV-irradiated yeast has implications for its ability to improve vitamin D status:  new data from an ODIN RCT.

There is a considerable mismatch between current intakes of vitamin D by many European populations and recommended target intakes for the vitamin [1]. While traditional fortification of milk and other dairy products remains important in tackling inadequate intake, additional strategic approaches to fortification, including biofortification, of a wider range of foods, have the potential to increase vitamin D intakes in the population [2]. The potential to fortify bread with synthetic vitamin D3 has been known for some time, and fortified bread has been shown to increase vitamin D status as effectively as vitamin D supplements in adult women [3]. The process of treating baker’s yeast with UV light enriches it in vitamin D2 and thus opens up major potential for vitamin D2-enhanced bread and other appropriate baked products. This vitamin D2-enriched UV-treated baker’s yeast was assessed by the EFSA Dietetic Products, Nutrition and Allergies (NDA) Panel in 2014 and was considered safe for use in yeast-leavened bread, rolls, fine pastry and food supplements [4]. Bread using this vitamin D-enriched UV-treated baker’s yeast has already made its way onto the market in some countries [5].  Data demonstrating that the vitamin D2 in bread made from this UV-treated baker’s yeast can increase vitamin D status has only come from a study in rats [6] thus far.  One of the aims of the ODIN project was to investigate the bioavailability of vitamin D2 from UV-irradiated yeast present in bread in an 8-week randomized controlled trial in healthy young adult women during winter. 

In an 8-week randomized controlled trial (called BreaD) by Itkonen and colleagues [7] at the University of Helsinki, Finland under the direction of Professor Christel Lamberg-Allardt, thirty-three healthy young adult women (aged 20–37 years) during winter (February–April) 2014 were divided into four study groups.  The groups were given different study products, either:

  • A placebo pill and regular bread  (providing 0 μg vitamin D2 or D3 per day);
  • A vitamin D2 supplement and regular bread (providing 25 μg vitamin D2 per day);
  • A vitamin D3 supplement and regular bread (providing 25 μg vitamin D3/d);
  • Or a placebo pill and vitamin D2-fortified bread (made with UV yeast) (providing 25 μg D2/d)

Serum 25-hydroxyvitamin D concentration (the indicator of vitamin D status) was measured at baseline, midpoint (week 4) and endpoint (week 8) using a CDC-certified liquid chromatography tandem mass spectrometry method at the Cork Centre of Vitamin D and Nutrition Research at University College Cork.  The mean baseline serum 25-hydroxyvitamin D concentration of the group of women was 65.1 nmol/L.  

The study showed that consumption of the UV yeast-vitamin D2-fortified bread did not affect serum 25-hydroxyvitamin D concentration (See Figure 1).  This was despite the fact that the bread, even following the baking process, was analysed and shown to actually contain the 25 μg vitamin D2.  The group receiving no additional vitamin D (placebo) likewise had no change in serum 25-hydroxyvitamin D concentration; whereas both the vitamin D2 and, even more so, the vitamin D3 supplement groups had significant increases in serum 25-hydroxyvitamin D concentration (by 9.6 and 17.0 nmol/L, respectively) [7].  Thus, this new data suggests that vitamin D2 from UV-irradiated yeast in bread, despite being present post baking, was not bioavailable in humans.

Click here to for the link to the full paper describing the full study and other interesting findings:

Figure 1.  Response of serum 25-hydroxyvitamin D concentration to 25 μg vitamin D per day in the form of UV yeast-D2-bread or vitamin D2 or D3 supplements over the eight-week study period. Time-points are at 4-week intervals, representing mean values at each time-point, error bars represent standard errors [7].



  1. Kiely M, Black LJ. Dietary strategies to maintain adequacy of circulating 25 hydroxyvitamin D concentrations. Scand J Clin Lab Invest Suppl. 2012;243:14-23.
  2. Cashman KD, Kiely M. Tackling inadequate vitamin D intakes within the population: fortification of dairy products with vitamin D may not be enough. Endocrine. 2016;51:38-46.
  3. Natri AM, Salo P, Vikstedt T, Palssa A, Huttunen M, Kärkkäinen MU, Salovaara H, Piironen V, Jakobsen J, Lamberg-Allardt CJ. Bread fortified with cholecalciferol increases the serum 25-hydroxyvitamin D concentration in women as effectively as a cholecalciferol supplement. J Nutr. 2006;136:123-7.
  4. Scientific Opinion on the safety of vitamin D-enriched UV-treated baker’s yeast.  EFSA Journal 2014;12(1):3520 [19 pp.].
  6. Hohman EE, Martin BR, Lachlik PJ, et al.  Bioavailability and efficacy of vitamin D2 from UV-irradiated yeast in growing, vitamin D-deficient rats. J Agric Food Chem 2011; 59: 2341-2346.