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Journal of the American College of Nutrition, Vol. 18, No. 6, 582-590 (1999)
Published by the American College of Nutrition

Original Research

Intakes of Vitamin C, Vegetables and Fruits: Which Schoolchildren Are at Risk?

Jeffrey S Hampl, PhD, RD, Christopher A. Taylor and Carol S. Johnston, PhD, RD, FACN

Graduate Program in Human Nutrition, Arizona State University, Tempe, Arizona

Address reprint requests to: Jeffrey S Hampl, PhD, RD, Graduate Program in Human Nutrition, Arizona State University, Box 872502, Tempe, AZ 85287-2502


   ABSTRACT
TOP
 FOOTNOTES
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 CONCLUSION
 REFERENCES
 
Objective: The purpose of this study was to determine vitamin C intakes among American schoolchildren. We investigated the leading sources of vitamin C in children’s diets, the leading vegetables and fruits consumed by children and differences in dietary intake associated with vitamin C consumption.

Methods: Data from 1,350 7- to 12-year-old and 908 13- to 18-year-old schoolchildren were obtained from the 1994–1996 Continuing Survey of Food Intakes by Individuals (CSFII). The children were stratified by age and gender and then split into three vitamin C consumption groups based upon two 24-hour recalls: low (0 to 30.0 mg), marginal (30.1 to 59.9 mg), and desirable (>60.0 mg). Data were analyzed by tabulation and by ANOVA followed by post hoc Scheffe’s test. Outcome measures included food groups and energy-adjusted intakes of micro- and macronutrients.

Results: Among the 7- to 12-year-olds, 12% of boys and 13% of girls had mean vitamin C intakes that were less than 30 mg/day, and, among 13- to 18-year-olds, 14% of boys and 20% of girls had low vitamin C intakes. In addition to consuming significantly more vitamin C, children with desirable vitamin C intakes also consumed significantly more (p <0.001) energy-adjusted folate and vitamin B6; children with low vitamin C intakes tended to have significantly greater (p <0.001) energy-adjusted intakes of fat and saturated fat. Children with desirable vitamin C intakes consumed significantly more (p <0.006) high-vitamin C fruit juice, low-vitamin C vegetables and whole milk. Children with low vitamin C intakes on average consumed two daily servings of vegetables and fruits, of which less than 1/5 of a serving was citrus, while children with desirable vitamin C intakes consumed an average of one daily serving of citrus.

Conclusions: A considerable number of children drastically under-consumed vitamin C and total vegetables and fruits. Overall, children with desirable vitamin C intakes had healthier diets, including more milk and vegetables, than did their peers with low vitamin C intakes. Health care professionals should continue to promote at least five daily servings of vegetables and fruits and should advise parents that at least one of these should be rich in vitamin C.

Key words: children, vitamin C, food consumption surveys, diet


   INTRODUCTION
TOP
 FOOTNOTES
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 CONCLUSION
 REFERENCES
 
Overt scurvy is not a common diagnosis in the United States or other industrialized countries [1]. Nevertheless, a review of the clinical literature reveals that scurvy may be resurgent, notably among children [2–5]. Brought on by low intakes of vitamin C, scurvy’s primary symptom is weakened collagenous tissue, which results in petechiae, bruising and hemorrhaging. Because of rapid development, children with scurvy also exhibit pathological changes in their bones, including osteoporosis, cortical thinning and epiphysiolysis [4].

Low intakes of vitamin C are no longer considered a national priority, and medical and allied health curricula typically teach that scurvy is a disease of the past or is found only in specific subgroups (e.g., alcoholics, institutionalized elderly) [2]. As a result, health care professionals are not trained to identify scurvy in the clinical setting [6]. Patients who present with scurvy generally are misdiagnosed with vasculitis, but they also may be diagnosed inappropriately with blood dyscrasias, ulcerative gingivitis or rheumatic disorders [5,6].

When plasma concentrations of vitamin C are marginal (0.2 to 0.5 mg/dL [11 to 28 µmol/L]), the body’s pool of vitamin C is depleted, and subclinical scurvy results [7]. Compared to overt scurvy, subclinical scurvy may be diagnosed even less readily because its symptoms are non-specific [1]. For example, marginal vitamin C status results in vague symptoms such as fatigue, irritability and impaired lung function [8,9]. Among adults, 25% of male non-smokers have marginal plasma vitamin C [7], but recent data regarding plasma and tissue levels of vitamin C in children are missing.

Previous research has reported children’s vitamin C intakes and consumption of vegetables and fruits [7,10–16]. However, studies that examine children’s vitamin C intake typically do not reveal which foods are their dietary sources of vitamin C. Those that do discuss dietary sources of vitamin C tend to use broad food group categories (e.g., vegetables), which fail to identify the important and rich sources of vitamin C in children’s diets [17]. Because so few foods actually are rich in vitamin C, knowing the contribution of these foods to total vitamin C intake is important for nutrition education and diet planning. This study was conducted to identify the foods that contribute to schoolchildren’s vitamin C intake and also to examine dietary trends among children who under-consume vitamin C.


   METHODS
TOP
 FOOTNOTES
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 CONCLUSION
 REFERENCES
 
The 1994–1996 Continuing Survey of Food Intakes by Individuals (CSFII) provided the study sample. These surveys, organized by the United States Department of Agriculture (USDA), were conducted as separate twelve-month surveys, which were then combined as one large data set and released on CD-ROM. All three years were used for these analyses. Trained interviewers under contract with USDA gathered household composition and demographic data from non-institutionalized men, women and children residing in all 50 states and Washington, DC. Methods used to conduct these multistage, stratified area surveys have been documented [18]. The overall response rate for individuals providing two dietary recalls was 76.1%.

Our study included data from 696 boys and 654 girls between the ages of seven and twelve years and 457 boys and 451 girls between the ages of 13 and 18 years. All participants were students (i.e., twelfth grade and below), and each provided two non-consecutive, multiple-pass 24-hour recalls as part of USDA’s data collection design [18,19]. The second 24-hour recall was completed between three to ten days after the initial 24-hour recall; CSFII protocol called for the second recall to be completed on a different day of the week than the first recall.

All children provided their own dietary intake data, but seven- to eleven-years-olds were assisted by the adult household member who was primarily responsible for preparing the child’s meals (generally, the child’s mother). If the child or primary caregiver could not provide suitable recall data, more detailed data regarding the child’s dietary intake were sought from another caregiver, such as a babysitter or from school foodservice personnel. The CSFII protocol permitted any number of caregivers to contribute to a child’s 24-hour recall so that complete dietary data could be obtained.

The USDA assigned a 7-digit code number to each food and beverage item reported as consumed and provided food groups to categorize them; however, the food groups were too broad for the purposes of this investigation because they did not readily identify high-vitamin C foods. Instead, each food and beverage item in the CSFII data base was re-coded and re-categorized into 48 discrete food groups using previous research as a guide [20]. Food groups were created to identify different sources of vitamin C and to differentiate between vitamin C-containing foods in a category. For example, we defined high-vitamin C fruits as fruits that provided at least 60mg of vitamin C per serving, while low-vitamin C fruits provided no more than 30mg per serving. Also, high-fiber and low-fiber grains were distinguished so that the nutrient density of the diet could be more carefully evaluated. Mixed dishes were classified according to their primary ingredient (e.g., macaroni and cheese was placed in the pasta category). Data involving the nutrient content of each food and beverage item were included in the CSFII data base when released by USDA.

The sample was stratified by gender and by age so that seven- to twelve-year-olds could be examined separately from 13- to 18-year-olds. The sample was then separated into groups based upon each individual’s daily vitamin C intake, averaged from the two 24-hour recalls: low (0 to 30.0 mg), marginal (30.1 to 59.9 mg) and desirable (>60.0 mg). The Recommended Dietary Allowance (RDA) for vitamin C ranges from 45 to 60 mg per day for seven- to 18-year-olds [21]. We chose to use a threshold of 60mg as a desirable intake for all children. The Panel on Dietary Antioxidants and Related Compounds of the Food and Nutrition Board is now in the process of determining the Dietary Reference Intake (DRI) for vitamin C [22,23], and there is ample evidence to support a dietary recommendation that takes into consideration not only vitamin C’s antiscorbutic activity but also its role in antioxidant defense and immune function [22,24].

The contribution to total vitamin C by each food group was determined using the following formula [25]: ({Sigma} total vitamin C mg from all foods in a group) ÷ ({Sigma} total vitamin C mg from all foods). To establish which vegetables and fruits were most frequently eaten, we used frequency analyses, which determined the number of times a serving of each food or beverage item was reported as consumed. The number of servings of vegetables, fruits and citrus fruits consumed by the children was obtained from a record type within the CSFII that sorts foods and beverages into the food groups of the Food Guide Pyramid [26].

Analysis of variance (ANOVA) followed by post hoc Scheffe’s analyses was used to compare food group and nutrient intakes by vitamin C consumption group. Energy-adjusted means of each individual’s two 24-hour recalls were used for analyses. Because the consumption of total nutrient intake is at least partially dependent on total energy intake and because the nutrient density of the diets is (in this instance) more relevant than actual gross intake, we adjusted for energy intake by computing nutrient intakes per 1,000kcal. Statistical comparisons were made for energy-adjusted carbohydrate, fiber, fat, cholesterol and sodium, as well as for each nutrient that has an established RDA or other DRI [21], with the exceptions of vitamins D and K, selenium and iodide, which were not included in the CSFII data base. The Statistical Package for the Social Sciences (SPSS 7.0, SPSS, Inc., Chicago, IL) was used for all analyses.


   RESULTS
TOP
 FOOTNOTES
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
CONCLUSION
 REFERENCES
 
The children were mostly white (72%) or black (16%), with the remaining children Native American, Asian or Pacific Islander or not specified. One third (33%) of the children lived below 150% of the federal poverty level and 37% lived in households with incomes that exceeded 300% of the federal poverty level. The CSFII did not collect data regarding cigarette use from children younger than 11 years of age, but among the 13- to 18-year-olds, 4% of boys and 7% of girls were current smokers.

Our analyses revealed that a considerable number of children had low intakes of vitamin C. Among the seven- to twelve-year-olds, 12% of boys and 13% of girls had mean vitamin C intakes that were less than 30mg/day. Among 13- to 18-year-olds, 14% of boys and 20% of girls consumed less than 30mg/day vitamin C. An even greater proportion of children had marginal vitamin C intakes. For both age groups, 21% of boys and 27% of girls daily consumed between 30mg and 60mg of vitamin C.

The leading contributors to vitamin C intake are presented in Table 1. The primary contributor to vitamin C intake was high-vitamin C fruit juice for both the seven- to twelve-year-olds (24% of total vitamin C) and the 13- to 18-year-olds (28% of vitamin C). A secondary contributor to vitamin C intake for both age groups was vitamin C-fortified fruit drinks. Together, high-vitamin C fruit juice and fortified fruit drinks provided more than 40% of total vitamin C intake to seven- to twelve-year-olds and more than 50% of total vitamin C intake to 13- to 18-year-olds.


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  		Table 1. Leading Contributors to Vitamin C Intake among Schoolchildren

 
Low-fiber grains were an important contributor to vitamin C intake among the seven- to twelve-year-olds, who derived 10% of their vitamin C intake from these foods. Although not rich in vitamin C, both low-fiber grains and low-vitamin C vegetables were important contributors to total vitamin C intake because they were frequently consumed. Similarly, french fries are not rich in vitamin C, but they did contribute a notable amount (3% to 4%) of vitamin C to the children’s diets.

Table 2 shows overall vegetable and fruit intake. The most commonly consumed vegetable or fruit was lettuce, which accounted for 7% and 11% of all vegetables and fruits consumed by the younger and older children, respectively. Among the seven- to twelve-year-olds, raw apples and bottled orange juice were commonly consumed, and each accounted for 6% of all vegetables and fruits consumed. Other leading vegetables and fruits consumed by the younger children were raw bananas, carrots, and tomatoes (each representing 4% of all vegetables and fruits consumed). Among the 13- to 18-year-olds, raw tomatoes and bottled orange juice were frequently consumed (each accounting for 8% of all vegetables and fruits). Secondary vegetables and fruits for the older children included raw apples, carrots and onions (representing 4%, 3% and 3% of all vegetables and fruits consumed, respectively).


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  		Table 2. Most Frequently Reported Vegetables and Fruits Consumed by Schoolchildren

 
Tables 3 and 4 present significant differences in energy-adjusted nutrient intakes found between the vitamin C-consumption groups. In addition to significantly higher energy-adjusted vitamin C intakes, children with desirable vitamin C intakes also consumed significantly more energy-adjusted folate and vitamin B6 (p <0.001), regardless of age or gender category. For seven- to twelve-year-old boys and girls, energy-adjusted intakes of total fat and saturated fat were significantly greater (p <0.001) among those with low vitamin C intakes. Furthermore, young girls with low vitamin C intake consumed significantly more energy-adjusted monounsaturated fat, phosphorus and protein (p <0.01). The 13- to 18-year-old girls—but not boys—with low vitamin C intakes had significantly higher energy-adjusted intakes of total fat (p <0.001).


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  		Table 3. Mean (± Standard Deviation) Daily Intake of Energy-Adjusted Nutrients by 7- to 12-Year-Olds

 

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  		Table 4. Mean (±Standard Deviation) Daily Intake of Energy-Adjusted Nutrients by 13- to 18-Year-Olds

 
Differences in food intakes based upon vitamin C-consumption category were also found, particularly among boys (Tables 5 and 6). In addition to high-vitamin C fruits and fruit juice, seven- to twelve-year-old boys with desirable vitamin C intake consumed significantly more low-vitamin C vegetables (p=0.003) and whole milk (p=0.006) than boys with low-vitamin C intakes. Young girls with desirable vitamin C intake consumed significantly more high-vitamin C fruits (p=0.012), high-vitamin C fruit juice (p=0.002) and whole milk (p=0.008).


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  		Table 5. Food Group Intakes among 7- to 12-Year-Olds

 

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  		Table 6. Food Group Intakes among 13- to 18-Year-Olds

 
Among the 13- to 18-year-olds, boys with low vitamin C intakes consumed significantly more whole chocolate milk (p=0.002), coffee or tea (p=0.01) and soft drinks (p=0.001) and less high-vitamin C fruit juice (p=0.005) than boys with desirable vitamin C intake. Older girls who consumed a desirable amount of vitamin C consumed significantly more high-vitamin C fruit juice (p=0.003) and low-vitamin C vegetables (p=0.001) than girls with low-vitamin C intakes.

The mean daily servings of vegetables and fruits consumed by the children are presented in Table 7. On average, the children daily consumed four servings of vegetables and fruits; however, on the continuum of vitamin C intake, children with low vitamin C intake had the lowest intakes of vegetables and fruits, with group means ranging from 1.99 to 2.54 daily servings. In contrast, the children with desirable vitamin C intakes had greater vegetable and fruit intakes, and group means ranged from 4.45 to 6.04 daily servings. There was a consistent relationship between intake of citrus fruits and vitamin C consumption. Those with desirable vitamin C intake consumed about one serving of citrus fruit per day. Children in the low and marginal vitamin C intake categories daily consumed less than 1/5 of a serving of citrus fruit.


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  		Table 7. Mean Number of Servings of Vegetables and Fruits Consumed Daily by Children

 

   DISCUSSION
 
In industrialized countries, mean and median intakes of vitamin C tend to be high and exceed the United States RDA. For example, Crawford et al. [14] and Roma-Giannikou et al. [15] reported mean intakes greater than 75 mg for eight- to eleven-year-old children, and Ballew et al. [10] reported mean intakes of vitamin C of 170 mg for 12- to 19-year-old Navajo participants. However, high average intakes obscure the fact that a considerable number of children under-consume vitamin C. By dividing our sample into three discrete vitamin C consumption groups, we were able to show distinct dietary differences associated with vitamin C intake.

Using the 1987–1988 Nationwide Food Consumption Survey (NFCS), Johnson et al. [13] reported that 11% of seven- to ten-year-olds consumed less than 77% of the RDA (45mg) of vitamin C. Although we used a threshold of 60mg of vitamin C as a desirable intake, we similarly found that 12% to 13% of children daily consumed less than 30mg of vitamin C. Our results are also similar to those of Ballew et al. [10], who reported that the 15th percentile of vitamin C intake among 12- to 19-year-olds was 20mg—far below the RDA. And Crawford et al. [14] reported that 13% to 16% of their sample members did not meet the RDA (45mg) for seven- to ten-year-old children.

In a Scottish study, McNeill et al. [12] used duplicate-diet analyses to determine the nutrient intakes of 12-year-old students. Interestingly, girls’ daily mean intake of vitamin C ranged from 22mg to 40mg (average for the week=30mg). The boys fared somewhat better with a mean intake of 47mg. Their sample size was small (n=36) because of the burden of keeping duplicate diets; nevertheless, most of these students would be classified as having low vitamin C intakes. The United Kingdom’s recommendation for vitamin C intake ranges from 30mg to 40mg for children and adults [27]. These amounts are considerably lower than those of the United States and—similar to our own—do not take into account vitamin C’s antioxidant activity. Possibly, the children’s low intakes of vitamin C are a reflection of their national standard, which does not encourage high intakes.

We found that high-vitamin C fruit juices and vitamin C-fortified fruit drinks were the leading contributors to vitamin C intake for children. All of the children in this study who consumed a desirable amount of vitamin C had significantly greater intakes of high-vitamin C juices than did their peers. These results are not surprising, given that vitamin C intakes correlate strongly (r=0.69, p<0.0001) with consumption of citrus juice [28]. Vitamin C-containing juices and drinks are popular, and they make important contributions to daily vitamin C intake; however, whether health professionals should recommend fruit juices as an important part of children’s diets is debatable [29].

Because of fears of obesity and short stature, health professionals have criticized the frequent consumption of fruit juice and juice drinks, warning parents to limit their children’s intake of these beverages to no more than twelve fluid ounces per day [30,31]. However, Skinner et al. [29] recently showed in a sample of young children that there were no significant associations between short stature or obesity and high juice intakes. They also noted an additional benefit of high fruit juice consumption. Children who drank more than twelve fluid ounces per day of fruit juice consumed 50% more vitamin C than children who consumed fewer than twelve fluid ounces per day, although children in both juice-consumption categories had vitamin C intakes that exceeded the current RDA.

Similarly to our findings, Skinner et al. [29] showed that most children were not indulging in fruit juice and that children consumed much more milk and soft drinks than fruit juice. Although fruit juice may not contribute to obesity and may not replace milk in the diet, there are other reasons to limit fruit juice consumption. Among American children and adults, fruit intake is low; of the fruit servings that are consumed, between one third and one half actually are fruit juice and not whole fruits [28,30]. Both fruit juices and fruit drinks have a high concentration of simple sugars and readily can lead to tooth decay; in contrast, whole fruits have low cariogenicity due to their low carbohydrate and high water content [32]. In addition to vitamin C, whole fruits contain other nutrients such as dietary fiber, which frequently is lacking in children’s diets.

An important source of both dietary fiber and vitamin C in children’s diets is low-fiber cereals [33]. Our category of low-fiber grains included sugary, ready-to-eat cereals, which often are fortified to provide less than 15mg vitamin C per serving. As noted by Subar et al. [11], ready-to-eat cereals provide vitamin C and other nutrients that would not occur naturally and therefore could be considered a dietary supplement. Any food that contributes to nutrient intakes should not be disparaged; despite their high-sugar content, low-fiber, ready-to-eat cereals do provide notable amounts of essential nutrients to children’s diets. Nevertheless, parents should encourage their children to try whole-grain cereals that provide less sugar and more complex carbohydrates in addition to vitamins and minerals.

We showed that children who had desirable vitamin C intakes consumed significantly greater amounts of energy-adjusted folate and vitamin B6, in addition to vitamin C, while those with low vitamin C intakes tended to consume significantly more energy-adjusted fat. Tonstad and Siversten [16] reported an inverse relationship between dietary vitamin C and fat, which they associated with an increase in vegetables and fruits as various dietary sources of fat decreased. This pattern also is conclusive for folate, which is found predominantly in vegetables and fruits. The fact that energy-adjusted intakes of fat were associated with low-vitamin C diets prompts some concern for these children’s long-term health. The current leading causes of death in the United States are cardiovascular disease and cancer [34]; both of these have been linked to dietary intake and may have their origin in childhood [35]. Because food preferences and eating habits may be established during childhood [36], parents should emphasize high-vitamin C vegetables and fruits when planning their children’s meals and snacks.

Interestingly, our results showed that seven- to twelve-year-old boys with desirable vitamin C intake consumed significantly more beef and ground beef dishes, accompanied by significantly greater intakes of vitamin B6. We did not expect vitamin B6 to be associated with high-vitamin C diets. This vitamin generally is coupled with dietary protein, and requirements for vitamin B6 rise as dietary protein increases [21]. These results imply that children are consuming vitamin C-containing foods as "camouflaged" foods. For example, Krebs-Smith et al. [37] reported that children often consume vegetables and fruits as part of mixed dishes (e.g., tomato sauce on pizza). In our study, low-vitamin C vegetables such as lettuce and onions used as condiments on hamburgers or sandwiches appear to contribute to vitamin C intake, and, evidently, these condiments contribute a great deal of vitamin C to children’s diets. We showed that the most commonly consumed vegetables and fruits included lettuce, tomatoes and onions—each of which is used as a condiment on sandwiches.

In a study of the vitamin C status of college students, Johnston et al. [38] found that 12% to 16% of students had marginal plasma concentrations of vitamin C. The students’ precarious vitamin C status was accompanied by a low intake of vegetables and fruits, which averaged about 2.5 daily servings. Their intake of vegetables and fruits was not much more than that of students with deficient plasma vitamin C, who consumed an average of one daily serving of vegetable or fruit. Our results showed that children’s mean intakes of vegetables and fruits are low, especially among children with low vitamin C intakes who averaged two daily servings of vegetables and fruits per day.

The National "5 A Day" Campaign and the Food Guide Pyramid recommend five to nine daily servings of vegetables and fruits [26,39]; however, neither of these prioritizes which vegetables and fruits should be consumed. Lettuce, onions, apples and bananas—some of the most frequently consumed vegetables and fruits reported here—are not rich in vitamin C. Children with desirable vitamin C intakes, on average, consumed one daily serving of citrus fruits, and we found that the only high-vitamin C "fruit" frequently consumed by the children was orange juice.

Citrus fruits are among the few foods that are rich sources of vitamin C, and parents should ensure that their children consume at least one high-vitamin C fruit as part of their "5 A Day." As a water-soluble vitamin, vitamin C is not retained well by the body. Johnston and Corte [40] recently showed that plasma vitamin C levels drop into the deficient or depleted range within one to three weeks when high-vitamin C vegetables and fruits are removed from the otherwise healthy diets of human subjects.

The number of smokers in our sample was too small for further statistical analyses; however, we did determine the prevalence of cigarette use because smoking during childhood and adolescence is a major public health issue. Similar to current demographic trends [41], we found that a greater proportion of girls than boys were current cigarette users, but our figures were considerably less than the estimated 32% of American adolescents who use tobacco products [42]. This may be a result of sampling bias because our sample included only schoolchildren, who are less likely to smoke than are delinquent or truant children [43]. Furthermore, CSFII data were collected from all household members, and teenagers in this sample may not have been willing to admit a smoking habit if their parents were present. Alternatively, some sample members may not have yet smoked 100 cigarettes during their lifetime; CSFII protocol, therefore, would not permit further questions to determine current smoking habits.

Approximately 3,000 children begin smoking every day in the United States [43], imposing additional exogenous oxidative stress on their bodies. Every puff of cigarette smoke contains 1014 low-molecular-weight free radicals [44]. Antioxidants such as vitamin C may have a protective effect against oxidative damage by scavenging oxidants in blood plasma and in tissues. Serum concentrations of vitamin C among smokers are about 25% lower than those of non-smokers [45,46], and Kallner et al. [47] reported that metabolic turnover of vitamin C was 40% higher among smokers than non-smokers. Children and adolescents who use tobacco products place themselves at risk for vitamin C hypovitaminosis and have the greatest need for dietary intervention.


   CONCLUSION
TOP
 FOOTNOTES
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 CONCLUSION
REFERENCES
 
Using recent food consumption data collected by USDA, we showed that a considerable number of children are drastically under-consuming vitamin C and total vegetables and fruits. Children with desirable vitamin C intakes consumed a single serving of citrus fruit per day; in contrast, children with low or marginal vitamin C consumed less than 1/5 of a serving of citrus daily. Overall, children with desirable vitamin C intakes had healthier diets and consumed more milk and vegetables than their peers with low vitamin C intakes. Health professionals should continue to recommend five to nine daily servings of vegetables and fruits; furthermore, the vegetables and fruits promoted should include at least one whole vegetable or fruit (not just juice) that is rich in vitamin C.


   FOOTNOTES
TOP
 FOOTNOTES
ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 CONCLUSION
 REFERENCES
 
This work was presented, in part, at the annual meeting of the Federation of American Societies for Experimental Biology, Washington, DC, April 19, 1999.

Received May 1, 1999. Accepted July 1, 1999.


   REFERENCES
TOP
 FOOTNOTES
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 CONCLUSION
 REFERENCES
 

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