Contributions of Dietary Vitamin D, Weight Status, and Skin Color to Vitamin D Status and Adherence to Vitamin D Supplements in At-Risk Youth.
Abstract: Vitamin D
is an essential nutrient for bone growth and development in children. In addition to its
skeletal effects, vitamin D may also reduce risks for a variety of diseases that can
affect children, including upper respiratory infections, autoimmune diseases, and
cardiometabolic diseases. Most circulating 25-hydroxyvitamin D (25OHD) comes from
exposure to UVB rays in natural ... read moresunlight. However, excess adiposity, dark skin
pigmentation, and other factors can impair this process. Under such circumstances,
dietary vitamin D becomes critically important for maintaining an adequate serum
concentration of this vitamin. The overall objectives of this dissertation were to
determine how vitamin D is affected by weight status, race/ethnicity, and skin
pigmentation and to understand the factors that promote adherence to vitamin D
supplementation in children who are at risk of deficiency. Specifically, the following
three Study Aims were addressed: 1) to examine the influences of weight status and
race/ethnicity on the association of total vitamin D intake with serum 25OHD in U.S.
children; 2) to determine the extent to which differences in skin color explain
racial/ethnic differences in serum 25OHD among schoolchildren; and 3) to examine the
determinants of adherence to vitamin D supplementation in schoolchildren at-risk for
deficiency. These associations were examined cross-sectionally through data collected
from that National Health and Nutrition Examination Survey (NHANES) 2005-2006 and the
Daily D Health Study (DDHS), a vitamin D supplementation study of 4th-8th grade
schoolchildren from racially diverse communities in the northeastern U.S. For Study Aim
1, vitamin D intakes and serum 25OHD were estimated in a national sample of 3,310
children and adolescents (ages 1-18 years) from the 2005-2006 NHANES. The majority (75%)
of U.S. children failed to meet current Estimated Average Requirements (EAR).
Overweight/obese children who failed to meet the EAR were five times more likely to be
at risk for inadequate 25OHD than children who met it (P<0.001). Black children with
intakes below the EAR were nearly four times more likely to be at risk for inadequate
25OHD than children who met the EAR (P<0.01). Study Aim 2 explored the relationship
between race/ethnicity and genetic skin color with serum 25OHD in a sample of 307
children (ages 9-15 years) from the DDHS. Race/ethnicity and skin color were similarly
predictive of 25OHD; however race/ethnicity explained additional variability in 25OHD
beyond skin color in this population (P=0.03). Study Aim 3 examined the determinants of
adherence to vitamin D supplementation in a sub-sample of 256 child and parent pairs
from the DDHS. Adherence was higher when parents took vitamin D-containing supplements
(7% higher, P=0.008) and also with combined child and parent administration of the
supplement compared to child only (9% higher, P=0.03), but was largely unrelated to
specific health beliefs. In conclusion, overweight/obese and black U.S. children who
were not consuming the EAR were more likely to be at risk for inadequate 25OHD. Our
findings also provide the first evidence that race/ethnicity captures additional
variability in 25OHD beyond genetic skin color. Finally, promoting parental involvement
may be a practical solution for health professionals aiming to improve supplement
adherence in at-risk youth.
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Food Policy & Applied Nutrition.
Advisor: Jennifer Sacheck.
Committee: Susan Harris, Johanna Dwyer, and Paul Jacques.
Keywords: Nutrition, and Epidemiology.read less