This study reports food sources of vitamin D among a large sample of African-American and white girls (ages 9–18) during 1987–1997 and the characteristics of girls that predicted individual differences in total daily vitamin D intake. Overall, total vitamin D intake was highly concentrated in milk and dairy products and fortified foods. There were age- and race-related differences in food sources of vitamin D with lower Vitamin D consumption by African-American girls at all visits. Breakfast consumption predicted higher vitamin D intake among all groups.
Very few foods contain vitamin D in its natural form and those that are the richest natural source of vitamin D (fatty fish and its oil) [33
] are not frequently consumed [40
], thus fortified foods (milk, margarine, cereals) can assist with vitamin D intake [33
]. In the NGHS, fortified milk and milk products were the most common food sources of vitamin D; milk provided over 42% of all vitamin D at all visits. These findings are in accord with national data [16
] demonstrating the important contribution of fortified milk to vitamin D intake in adolescence.
Meats (primarily fatty fish, pork) and beans (meat alternatives) provided the distant second richest supply of vitamin D, across all NGHS visits. Consistent with past research [43
] naturally rich sources of vitamin D in the meat and beans group (particularly fatty fish) were consumed by a small percentage of girls in the NGHS.
RTE fortified cereal, combining all brands, contributed approximately 9% of the mean vitamin D intake in the NGHS, comparable with the 5%–10% documented by the 1999–2000 National Health and Nutrition Examination Survey (NHANES) [34
]. Since milk and RTE cereal are often consumed together, these foods provide over half of the vitamin D intake from foods. Previous studies reported that for both African-American and white females [24
], consumption of fortified food sources of vitamin D [milk and cereal] was associated reduced the occurrence of vitamin D insufficiency.
Ethnicity, breakfast consumption, age (represented by visit), and energy intake were factors that predicted differences in total vitamin D intake in girls in the NGHS. The current and previous NGHS findings [45
] add to the growing evidence that racial disparities exist in vitamin D intake [31
]. In agreement with past studies [37
] African American girls consumed less fortified milk compared with their white counterparts, perhaps partly attributed to lactose intolerance known to be common in this ethnic group [31
]. White girls more often consumed lower-fat milks whereas African-American girls more often obtained vitamin D from higher fat milks, higher fat meats and meat alternatives (sausage, ground beef, eggs), and margarine. Improving vitamin D intake from low saturated fat and cholesterol sources, especially lowfat/nonfat milk, dairy products and possibly other fortified foods such as margarine and soymilk, may be especially helpful [44
] among African Americans who are at higher cardiovascular risk but often avoid these foods [48
All girls reduced milk and dairy intake with age, suggested as possibly being associated with decreased family influence on dietary habits [50
]. Milk is increasingly displaced with soft drinks, fruit juices, and/or fruit drinks as children age [52
]. Increased frequency of breakfast skipping also occurs in adolescence [55
], especially among African-American girls [55
Few girls in NGHS used supplements and their use decreased over time ranging from approximately 10% to 7% from mid- to late-adolescence, respectively. Approximately one-third of adolescent girls in the 1999–2000 National Health and Nutrition Examination Survey and one-quarter of the 2,761 adolescents surveyed in the 2001–2002 Child and Adolescent Trial for Cardiovascular Health Study [59
] reported using multi-vitamin, multi-mineral supplements Whether supplements should be recommended to improve vitamin D insufficiency requires further investigation.
Study limitations include the absence of data regarding sunlight exposure and the self-reported dietary intake data subject to recall errors and underreporting [60
]. Also NGHS did not report serum levels of 25-hydroxyvitamin D that could further help to differentiate bioavailability of these self-reported dietary sources.
Strengths, including the longitudinal nature of this study, a high follow-up rate and detailed dietary intake data enhance the value of this study. Diet assessment was performed by trained and certified dietitians using validated three-day food records, including a weekend day and two week days. The longitudinal study design reduces both between and within-subject variability and implicitly controlled the seasonal component of dietary intake [61
], because recruitment into the study and dietary recall collection occurred throughout the year.
Findings from the National Heart, Lung and Blood Institute Growth and Health Study document that milk and dairy products provided the majority of vitamin D intake with sources differing by race. African-American girls [33
] reported a significantly lower intake of vitamin D from both food sources and supplements, compared with white girls. Given the important function of vitamin D in skeletal health and its emerging role in the prevention of chronic diseases [32
], food and nutrition professionals should renew efforts to educate adolescents, especially African Americans, to consume a healthful diet by choosing a wide variety of nutrient-dense foods and beverages, especially those that provide vitamin D.