Vitamin D deficiency, 25-hydroxyvitamin D less than 50 nmol/L, is common in the US population around 41.6% 1. The main source of vitamin D is sunlight. During winter at latitudes above 40 degree N, people cannot synthesize vitamin D 2; therefore, food becomes the main source of vitamin D. The study presented that vitamin D –fortified milk and bread reduced the decline of vitamin D level during winter in both children and adult and maintained 25(OH)D level in normal level 3.
The research studied the effect of vitamin D-fortified milk and bread on vitamin D level in both children (aged 4-17 yrs.) and adults (aged 18-60 yrs.) during 6 month winter period in Denmark by using 25-hydroxyvitamin (25(OH)D) as an indicator for vitamin D status. In the group receiving vitamin D-fortified milk and bread, 78% of children (median 8.0 μg/day) and 56% of adult (median 5.8 μg/day) met the vitamin D intake recommendation of Nordic Council (7.5 μg/day), but only 2% in the control group consumed vitamin D to meet the requirement. The vitamin D level decreased in both groups (fortified diet and control). The vitamin D fortified milk and bread group showed 25(OH)D level decreased from 73.1 nmol/L to 67.6 nmol/L, and from 71.1 nmol/L to 41.7 nmol/L in the control group.
This study shows strength because it obviously explained the study question, method, and result, for responding the effect of vitamin D fortified milk and bread on vitamin D status. Moreover, the study design is a good model for further study about effect of fortified food with the family and the real-life based design, which decrease dropout rate and increase compliance. However, the weakness of this study is that the research cannot force participants to intake a fortified diet to meet the requirement. The study didn’t include the population with high risk of vitamin D deficiency such as elderly or post-menopausal women. Therefore, this study cannot apply the effect of vitamin D-fortified food on vitamin D status to all population groups.
Previous researches presented the effect of vitamin D-fortified food in milk differently. The study from New Zealand 4 reported that fortified milk with 5 μg /day vitamin D in healthy women reduced the decreased 25(OH)D level in fortified group. The study suggested that vitamin D 5 μg /day was inadequate to prevent the decreased 25(OH)D with the season change and low sunlight exposure. The study about vitamin D-fortified milk in schoolchildren in Mongolia 5 reported that supplement or fortified milk with 300 IU (7.5 μg) per day for 3 months increased 25(OH)D level, but the level is below 50 nmol/L. Furthermore, the research about effect of vitamin D-fortified bread in healthy women for 3 weeks from Denmark6 showed that the group receiving bread fortified with vitamin D 10 μg daily increased 25(OH)D level. The three studies presented that vitamin D-fortified in milk or bread with cholecalciferol (vitamin D3) increased 25(OH)D level the same as this study. Moreover, the different doses of vitamin D-fortified diet in study from Mongolia and Denmark increased the 25(OH)D concentration, but 25(OH)D level is still below 50 nmol/L. Similar outcomes of this study and the study from New Zealand may come from the normal 25(OH)D level at baseline while the 25(OH)D level at baseline in others is below normal level. Moreover, no study can provide the effective amount of vitamin D fortification in diet to prevent the reduction of 25(OH)D level when season changed.
The study showed that participants who intake milk and bread with vitamin D fortification could maintain normal vitamin D level during winter period. Therefore, people who risk to vitamin D deficiency should monitor their vitamin D intake and choose the food product with vitamin D fortification such as milk, yoghurt, cheese, bread, or orange juice. The form of vitamin D in supplement people select should be cholecalciferol (vitamin D3).
- Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res. 2011; 31: 48-54.
- Kimlin MG. Geographic location and vitamin D synthesis. Mol Aspects Med. 2008; 29: 453-61.
- Mitry D, Bunce C, Wormald R, Bowman R. Childhood visual impairment in England: a rising trend. Arch Dis Child. 2013; 98: 378-80.
- Green TJ, Skeaff CM, Rockell JE. Milk fortified with the current adequate intake for vitamin D (5 microg) increases serum 25-hydroxyvitamin D compared to control milk but is not sufficient to prevent a seasonal decline in young women. Asia Pac J Clin Nutr. 2010; 19: 195-9.
- Rich-Edwards JW, Ganmaa D, Kleinman K, et al. Randomized trial of fortified milk and supplements to raise 25-hydroxyvitamin D concentrations in schoolchildren in Mongolia. Am J Clin Nutr. 2011; 94: 578-84.
- Natri AM, Salo P, Vikstedt T, et al. 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.
Reviewed by Emilee Firth