2012 Annual Report
1a.Objectives (from AD-416):
Objective 1: Determine the absorption of dietary calcium, magnesium, iron and zinc in children and the influence of other nutrients and dietary factors on the absorption.
Sub-objective 1.A: Evaluate the effects of supplemental vitamin D in enhancing calcium absorption in healthy children 4 to 8 yrs of age.
Sub-objective 1.B: Assess the absorption of magnesium and zinc in healthy children 4 to 8 yrs of age.
Sub-objective 1.C: Determine the effects of a diet lacking in meat (lacto-ovo vegetarian diet) on iron status in small children using a highly precise stable isotope method to measure iron status as determined by absorption of iron (reference dose).
Objective 2: Determine the effect of dietary components on the upregulation of intestinal iron transporter genes in human models.
Sub-objective 2.A: Test the quantity of a food component that must be provided and the duration of exposure to the Caco-2 cells that is needed to obtain a change in expression of the divalent metal transporter (DMT1) and the brush border ferrireductase (Dcytb) genes involved in iron absorption.
Sub-objective 2.B: Apply micro-array technology, once the appropriate conditions have been determined, to identify other intestinal genes that are affected by dietary components.
Sub-objective 2.C. Evaluate foods that contain the food component(s) in question to assess if the food component is able to alter gene expression in a food matrix. This would indicate that the digestion procedure is able to release the food component(s).
Objective 3: Evaluate multiple roles of Vitamin C and ocido-reductases in molecular regulation.
Objective 3: Characterize dynamic indices of bone formation by quantitative histomorphometry and micro computed tomography in 7 mouse models developed in our laboratory.
Objective 4: Quantitate specific gene expression by qRT-PCR in calvarial osteoblasts derived from appropriate models to clarify the specific roles of each knockout gene.
Objective 5: Determine the effects of castration, iron loading, ASC feeding and plant derived antioxidants on bone parameters in vivo.
1b.Approach (from AD-416):
The goal of our research is to provide data to enhance the development of nutritional guidelines, especially as related to mineral nutrition, in children. Using both human experimentation and cell culture models, we are studying methods of delivering the key minerals of calcium, zinc, and iron in the diet so as to optimize health outcomes. This is done by evaluating enhancers of mineral absorption, such as ascorbic acid, prebiotic fibers, and vitamin D and by considering nutrient:nutrient interactions that may limit mineral absorption such as an excess in the zinc:copper intake ratio. We will conduct a controlled trial of vitamin D supplementation to assess the effects of vitamin D status on calcium absorption in small children. We will evaluate different types of whole diets (lacto-ovo vegetarian) on iron status and the effects of differing intakes of zinc on zinc and copper absorption. We will determine if benefits previously seen for prebiotic fibers in enhancing calcium absorption also occur for iron absorption. These studies will utilize stable isotope techniques so as to provide accurate, practically applicable information that may be obtained from the study populations in a safe manner. In vitro studies will seek to identify genetic basis for mineral absorption and to develop appropriate models for evaluation of mineral absorption. Taken together, this project will provide novel information directly useful to government, industry, and the consumer related to dietary requirements. These data will have global application and provide a strong basis for evidence-based nutritional recommendations to be developed. Additional studies will explore the roles of aldose reductase and aldehyde reductase in modulating oxidative stress in cells, as well as their separate role in providing the starting substrates for the ascorbate synthesis pathway in mice. As a result we will have a better understanding of the role and importance of vitamin C in our diet.
During the year for Objective 1 we completed, analyzed, and presented at a major national meeting our research into the effects of vitamin D supplementation in 4- to 8-year old children. Our work this year included completing stable isotope studies of calcium absorption, as well as measurements of magnesium and zinc absorption in these children. These studies have been fully analyzed using mass spectrometry, and we are completing our interpretation of the research results.
Related to the calcium and vitamin D aspect of the study, we found that calcium absorption was not affected by providing either a placebo or a 1000 IU/day supplement to the children for about 2 months. This means that the recommended daily amounts (RDA) of 600 IU/day is likely more than adequate, as the dietary intake in these children was only about 200 IU/day.
Bone mineral content studies also were performed at baseline in these children. Of interest is that there was an apparent relationship between bone mineralization and magnesium, but not calcium or vitamin D intake in these subjects. Further analysis of this information is ongoing.
During this past year, we have also begun our study of iron absorption in vegetarian children. These studies will be completed entirely by this fall, and analysis and interpretation of the studies will then be conducted.
For Objective 2, studies with a human cell culture model were continued to more fully understand how different food components affected the expression of iron absorption related genes. Studies with different iron concentration treatments were continued from the previous year. Problems with analytical techniques slowed our progress and allowed only partial completion of our current year's milestones to fully characterize the effects of different food components on gene expression in our cell system.
This year, we conducted an extensive literature review of in vitro bioaccessibility and bioavailability methods for iron, other required minerals, and vitamins, as well as for various health-beneficial dietary polyphenols. We developed and submitted a review article, with an emphasis on the use of cell culture models, which assessed how these cell-based models could be applied to generate a better understanding of nutrient uptake parameters. This understanding will be valuable as we continue to move forward with our gene expression studies.
Effects of vitamin D supplementation in children. The importance of vitamin D for ensuring the health of children has long been understood. Over time, however, dietary recommendations for vitamin D intake have varied, with some eras seeing higher levels recommended and some lower. Researchers at the Children's Nutrition Research Center in Houston, Texas, analyzed data and have shown conclusively that giving healthy children an extra 1000 IU/day of vitamin D, although likely safe, has no benefit to calcium absorption and therefore cannot be advocated on bone health grounds. This means that caregivers do not need to emphasize the use of high-dose supplements above the recommended daily amounts (RDA) for children. This information has benefits to the dairy industry whose products are key in providing adequate, but not excessive, vitamin D for children.