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Nutrition and Aging

Reasonable Estimates of Serum Vitamin E, Vitamin C, and ß-Cryptoxanthin Are Obtained with a Food Frequency Questionnaire in Older Black and White Adults¹

Christy C. Tangney^*,2, Julia L. Bienias^,**, Denis A. Evans^,** and Martha C. Morris^,**

^* Department of Clinical Nutrition, Rush Institute for Healthy Aging, and ^** Department of Internal Medicine, Rush University Medical Center, Chicago, IL 60612

²To whom correspondence should be addressed. E-mail: ctangney{at}rush.edu.

	ABSTRACT

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Few studies provide correlations between different indicators of the dietary intakes of older (65 y) black and white adults. This study compared the usual intakes of vitamin E, vitamin C, and selected carotenoids estimated by a modified Harvard food frequency questionnaire (FFQ) to those estimated by multiple 24-h recalls, and to blood concentrations of components in a randomly selected sample of participants in the Chicago Health and Aging Project (CHAP). Subjects (n = 59) were interviewed to complete multiple 24-h recalls over a year’s time, then completed an FFQ and subsequently provided a fasting blood specimen within 2 mo. Dietary estimates were energy-adjusted separately for men and women. Significant (P < 0.05) correlations between total (diet and supplement) FFQ estimates and serum measures of vitamin E and vitamin C were as follows: 0.49 and 0.39 for blacks, and 0.42 and 0.29 for whites, respectively. The highest correlations between serum and FFQ indicators were for dietary ß-cryptoxanthin (0.46), total -tocopherol (0.46) and total ß-carotene (0.44) among whites; among blacks, the highest correlations were for dietary -carotene (0.81), total -tocopherol (0.53) and total ß-cryptoxanthin (0.50); all were significant (P < 0.05). Further adjustment for age, gender, BMI, and educational level minimally altered these coefficients. These findings indicate that the modified Harvard FFQ provides reasonable estimates of serum levels of vitamin E, vitamin C and ß-cryptoxanthin among CHAP participants.

KEY WORDS: • vitamin E • vitamin C • food frequency questionnaire • serum measures • validation

Few studies of older populations report correlations between nutrient levels obtained from self-administered food frequency questionnaires (FFQs)³ and plasma and/or serum levels (1–4). Even fewer include correlations for black adults, and these focus on antioxidants in middle-aged adults (5–7). Comparisons of blood levels with estimates of food carotenoid intakes are reported with a variety of dietary instruments, including the Block FFQ (3,6–11), the Harvard FFQ (1,4,12–15), multiple diet records (8,10,13,16), and repeated 24-h recalls (5,6,15,17). Three studies (two from the Framingham Heart study with a self-administered FFQ (1,4) and one from the Beaver Dam Eye study with an interviewer administered FFQ (3) were conducted with older subjects, but information on race was not provided.

In the present study we compared the serum concentrations of vitamin E (- and -tocopherol), vitamin C (ascorbic acid), and vitamin A (retinol), and selected carotenoids with the intakes of these dietary components estimated by two instruments, a modified Harvard FFQ and repeated 24-h dietary recalls. Our sample was drawn from the Chicago Health and Aging Project (CHAP), a biracial community study of persons aged 65 y. This study examined whether the usual intakes of these components as measured by the FFQ correlated with blood concentrations in older black and white participants of the CHAP study.

	SUBJECTS AND METHODS

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
    Population. Participants were selected from CHAP, a study of 65-y-old residents of three contiguous neighborhoods on the south side of Chicago. From 1993 to 1997, a door-to-door census identified 8509 age-eligible residents, of whom 6158 participated in in-home interviews about their health and lifestyle. A modified self-administered FFQ was distributed to all study participants at a mean of 1.8 y after the baseline interview; 95% of the survivors (84% of all CHAP participants) completed the assessment. A more detailed description of the original study has been published elsewhere (18). The study was approved by the Rush University Medical Center Institutional Review Board.

    Validation sample selection. A random sample stratified by race was drawn from the larger CHAP population to study the reproducibility and validity of the CHAP FFQ (19). A total of 232 subjects were able and willing to be further interviewed by a trained assistant who conducted in-person 24-h recalls (20) in participants’ homes every 2 mo over the ensuing 12 to 14 mo. Participants also completed the CHAP FFQ at the beginning and the end of that year.

A second random sample stratified by race was drawn from the validation study participants for the collection of a fasting blood sample at the end of the 12-mo period. A total of 63 of the selected 118 participants agreed to provide a blood sample, and 59 participants met the prespecified criteria that blood samples be provided within 2 mo of completing the second FFQ.

    Dietary assessment. The CHAP FFQ was adapted from a Harvard FFQ that was originally developed for self-administration by school-age children (21). The 156-item questionnaire included questions regarding the usual consumption of 139 food items and vitamin and mineral supplements over the past year, plus additional questions about dietary behaviors (22). The interviewers distributed the FFQ at the end of the final dietary recall interview in mo 12. Participants were instructed to complete the FFQ at their convenience and return it by mail, using the stamped, addressed envelope provided.

Trained research assistants conducted 2 to 6 in-home interviews with each participant to obtain 24-h recalls, using computer-assisted interactive software developed by the University of Minnesota [Nutrition Data System, food database version 13A and nutrient database 28; Nutrition Coordinating Center (NCC), University of Minnesota, Minneapolis] (20). The research assistants usually requested in-home interviews for the 24-h recalls only 2 h in advance of the visits, in order to minimize the possibility that participants would alter their dietary intakes. Household measures and the participants’ own dishware were used to estimate portion sizes. Brand names were solicited whenever possible. Recalls were reviewed weekly by specially trained nutritionists who were certified by the NCC. Nearly 40% of these coded recalls were also reviewed and analyzed independently by the NCC staff for quality control.

The validation study began in September 1997 and ended in January 2001. Visits to obtain blood from consenting participants began in December 1998. The 59 subjects completed a mean of 4.1 recalls: 6 subjects completed 2 recalls, 7 completed 3 recalls, 28 completed 4 recalls, 9 completed 5 recalls, and 9 completed all 6 recalls. The primary reason for failing to complete all 6 recalls was illness.

    Laboratory analyses. Fasting blood specimens were collected in the morning by a single trained phlebotomist. Specimens were collected in two vacutainer tubes. The tubes were shielded from daylight and kept in a cool pack until delivery to the laboratory, usually within 2 to 3 h of venepuncture. Blood samples in the EDTA vacutainers were centrifuged at 4°C, and plasma aliquots were obtained for the assessment of plasma cholesterol, triglycerides, and fatty acids in the cholesterol ester fraction. After centrifugation of the second vacutainer (SST vacutainers; Allegiance Healthcare), aliquots were also obtained for retinol, carotenoid, and tocopherol analyses. For the vitamin C assay, aliquots of serum were treated with freshly prepared metaphosphoric acid solution (100 g acid/L). All aliquots were stored at -80°C in cryogenic vials for a maximum of 2 y. Serum ascorbic acid levels are stable for up to 2 y if the protein is precipitated with metaphosphoric acid immediately before freezing (23).

Serum retinol, -tocopherol, -tocopherol, -carotene, ß-cryptoxanthin, ß-carotene, lycopene, and lutein + zeaxanthin levels were quantified by HPLC at Dr. Phyllis Bowen’s laboratory at the University of Illinois at Chicago, under the direction of Dr. Stacewicz-Sapuntakis. This group previously demonstrated stability, reproducibility, and validity of results (24). To make comparisons with the findings of others, we defined total vitamin E concentration as the sum of the -tocopherol and -tocopherol levels; this differs from recent definitions by the Food and Nutrition Board (25). Serum vitamin C concentrations were assayed at Dr. Tangney’s laboratory, using a modification of the Roe and Kuether method used by the second Health and Nutrition Examination Survey (26). Plasma levels of cholesterol, triglycerides, and fatty acids of cholesterol esters were measured using standard enzymatic techniques at Dr. Martha Wilson’s laboratory at Wake Forest School of Medicine, Winston-Salem, NC (27,28).

    Nutrient analyses of diet recalls and FFQs. Nutrient analyses of the 24-h recalls were performed using the University of Minnesota’s Nutrition Data System, version 2.92 (food database version 13A and nutrient database 28). The FFQs were optically scanned and analyzed using the Harvard nutrient database, which is continually updated using the USDA Nutrient Database for Standard Reference series, with additional updates from manufacturers and McCance and Widdowson’s The Composition of Foods (29,30). Additional data on the carotenoid composition of foods were obtained from the USDA–National Cancer Institute carotenoid database (31) and were provided for the FFQ analyses, but not for the recall data. For some of the food items, natural portion sizes (e.g., 1 slice of bread, 1 egg, 1 banana) were used to determine nutrient content. Otherwise, nutrient content was based on the mean portion sizes reported by the oldest participants (65–74 and 75 y) in the National Food Consumption Surveys, 1977–1978 (8,32–34). The daily intake of each dietary component was computed by multiplying the nutrient content of the food item by the reported frequency of intake, and summing over all food items. All dietary values were either log- or square root–transformed for better-fitting normal distributions. All dietary estimates for individual nutrients were energy-adjusted separately for males and females according to the regression residual method of Willett and Stampfer (35). Total intake was defined as the contributions from both food and supplements.

    Other data. Nondietary information was collected at the CHAP baseline population interview. Age was computed from the date of the 12-mo FFQ and the self-reported birthdate. Educational level was based on the response to a question on the highest grade or year of regular schooling. Height was self-reported. Interviewers measured each participant’s weight (without shoes) on a digital free-standing scale placed on a flat surface. The BMI was calculated from these measurements [weight/height² (kg/m²)]. Smoking status was based on the response to a question regarding current smoking. Alcohol use was coded as any reported use (in g) in the past year or none. The Mini-Mental State Examination (36) was administered at the population interview closest in date to the 12-mo FFQ.

    Statistical analyses. All statistical analyses were performed using SAS software (release 8; SAS Institute). An a priori level of significance was set at P = 0.05. Comparisons of dietary estimates by racial group (black or white), gender (female or male), and educational level (12 or >12 y) were made with unadjusted and energy-adjusted transformed values using t tests. For other comparisons of proportions (i.e., supplement use), chi-square tests were used. For each nutrient or dietary component, Pearson correlations were used to estimate associations between the dietary estimate and the serum measure, as well as associations with age, BMI, and education (in y). Either log or square root transformations of dietary estimates and biomarkers were used to improve normality. Where indicated, serum analytes were "lipid-adjusted," whereby the serum biomarker level is the residual obtained from regression models with the crude biomarker regressed on plasma total lipids (sum of plasma cholesterol plus triglycerides levels) (37). We reserved the term crude for biomarker levels that were not lipid-adjusted in this manner.

Correlations were analyzed separately for black and white participants, partialing for gender, educational level, age, and BMI. Similarly, correlations were analyzed for men and women, partialing for race, educational level, and age. Dietary estimates were adjusted for total energy intake using the residual regression method (35).

	RESULTS

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
    Subject characteristics. Participants included 29 black (17 female, 12 male), and 30 white (17 female, 13 male) subjects, ranging in age from 65 to 87 y (11 80 y; Table 1). More than half the participants (n = 33) had 12 y of formal education, and black subjects had markedly fewer years of education than whites in this sample. There were no important differences in age by race, by gender, or by educational level (the latter not shown). There were more smokers among blacks than whites and among men than women, and more men reported using alcohol than did women. Use of the individual vitamins A, E, and C was markedly greater among whites than blacks. Women reported ingesting vitamin A more often than did men, although a higher percentage of men reported using vitamin C and ß-carotene supplements.

	DISCUSSION

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Because short-term memory declines with age, the reliability of multiple 24-h recalls among older adults is often questioned (38). Multiple 24-h recall interviews may burden respondents, contributing to low participation rates and compromising general applicability. The FFQ may provide a more accurate picture of usual intake, because recalling foods frequently consumed may pose less of a challenge to participants than does recalling specific items consumed during the previous 24 h. The FFQ requests a more generic representation of intake (39). Comparison of intakes of key dietary components to sensitive biomarkers provides a criterion-related validation of the FFQ. Biomarkers are subject to error as well (40), but such errors are independent of those inherent in 24-h recalls and FFQs.

Our study was designed to assess the performance of the modified Harvard FFQ with older persons of two races, differing cognitive abilities, and differing educational backgrounds. The literature provides few data regarding this information. The correlations with serum analytes suggest that the CHAP FFQ provides reasonably valid estimates for vitamin E, vitamin C, and ß-cryptoxanthin intakes in black and white older adults. There were also moderately high correlations for total ß-carotene intake among whites and for -carotene intake among blacks. Correlation pairs for total -tocopherol and total vitamin E were similar whether FFQ or multiple recalls were used as the comparison, but these relations were less consistent with respect to vitamin C and ß-carotene.

The correlations reported for individual carotenoids in the CHAP study were in the range reported by other studies (1,3,6,9,14,40). Correlations of total ß-carotene intakes with serum levels in CHAP white adults (Table 4) were slightly higher than those reported by Brady and co-workers (r = 0.21) (3), Ritenbaugh et al. (r = 0.32) (14), and Peng and co-workers (r = 0.35) (9) and considerably higher than those reported for younger Dutch subjects (20 to 70 y; r = -0.14 to 0.17) (41). Moreover, correlations of total ß-carotene intakes with serum levels of CHAP white participants (though not those of CHAP blacks) were similar to those reported for the slightly younger black participants (mean age 43 y, range 18–87 y) in the Eat for Life trial (6). For other carotenoids, there were higher correlations for -carotene (CHAP blacks, r = 0.77 vs. Eat for Life, r = 0.34) and ß-cryptoxanthin (CHAP black adults, r = 0.49 vs. Eat for Life, r = 0.26), whereas both studies poorly captured lycopene intake estimates for blacks, with correlations close to 0. The correlation pairs for ß-carotene, ß-cryptoxanthin, and lycopene in CHAP whites are similar to those in elderly whites in Framingham (1). These correlation coefficients are also consistent with those reported for 162 predominately white men and women in the University of Arizona study (mean age = 57 y) (14).

As in the present study, poor correlations (r = 0.02 to 0.10) between total retinol intakes and serum levels were noted by several groups (9,40,42,43). The racial makeup of the subjects was not identified in any of these studies. As stated earlier, because serum retinol levels are closely regulated (44), stronger correlations were not expected.

With respect to other studies of vitamin E estimates acquired by an FFQ, three groups (2,9,42) reported correlations with serum measures that were slightly lower or similar (r = 0.41 to 0.60) to those reported for either racial group in the present study. The CHAP correlations were considerably higher than those reported by the Dutch group (r = 0.29 and 0.14 for men and women, respectively), in which considerably fewer older adults were represented (41). The CHAP correlations for total vitamin C were lower than those reported by Jacques et al. (42) for men and women 40 to 83 y of age (r = 0.44). Again, no racial information was provided about the participants, and a dietitian administered the FFQ to all participants in the latter study.

In contrast to studies with FFQs and serum biomarkers in older adults, even fewer reports compare estimates from repeated recalls to biological measurements of vitamins E and C and selected carotenoids. Once again, we found that the correlations between total ß-carotene intakes and serum levels in CHAP older blacks (Table 5) were similar to those reported for middle-aged blacks in the Eat for Life trial (r = 0.31) (6). This association is also of similar magnitude to that reported for younger participants of other studies (15,45,46). We found no studies of older adults in which total vitamin C intakes were estimated by repeated 24-h recalls. However, the unadjusted and energy-adjusted correlations for black CHAP participants were akin to those reported for slightly younger black adults (mean age 47 y; r = 0.19). Those for our CHAP white adults were stronger than those reported for the younger white participants (mean age 53 y; r = 0.17) in the Seventh Day Adventists study (5). Two other reports on younger European adults noted stronger relations (r = 0.50 and 0.35, respectively) (45,46). As in the present report, blood levels of vitamin E were highly correlated with total vitamin E intakes estimated from an average of 8 unannounced recalls in the Seventh Day Adventists study (r = 0.52 and 0.47 for blacks and whites, respectively) (5). In other reports using younger subjects and fewer recalls (15,42,43), correlations for vitamin E were much lower (r = 0.15 to 0.36). A lower correlation was also reported for nonsmoking Mediterranean adults (18 to 75 y of age; r = 0.15) (47).

In summary, correlations between the CHAP FFQ and serum levels were highly consistent with those reported by other groups, as were those between recall estimates and biomarkers. In many cases, the correlations exceeded those reported for other younger or similarly aged study subjects (2,3,5,6,9,41,42,47). These findings are particularly compelling because the CHAP FFQ was largely self-administered (only 2 of 59 subjects required interviewer assistance to complete the FFQ). In contrast, in other studies (2,42), dietitians or skilled interviewers administered the FFQ. We found no consistent differences in the magnitude of correlations between the two dietary tools among either racial group. Compared to the potentially higher respondent burden of multiple recalls, the self-administered CHAP FFQ appears to be an excellent method for garnering relative dietary exposures in large surveys of older adults.

The present validation effort has several strengths and several shortcomings. As a strength, the study sample was a random sample from a large biracial community. Second, the CHAP FFQ is largely self-administered. Most large-scale surveys or trials do not have the resources to interview participants. Finally, dietary and serum data represent much needed information about older blacks and whites. However, the desired number of multiple recalls was not acquired from every subject. This limitation reflects the difficulties in performing these assessments in a study population, especially when prior scheduling of the visit is not permitted. Although the in-house interviews may have prevented dropouts across time, this protocol component was also costly. Another major drawback was the small number of participants that provided blood samples. Thus, caution concerning the interpretation of the findings is required, especially among the subgroups.

In conclusion, the CHAP questionnaire appears to provide reasonably valid exposure information about several carotenoids, vitamin E and vitamin C. Further work is needed to confirm and expand our findings concerning the relations between such FFQs and other measures, such as blood serum levels for the subgroups, including the oldest old, the cognitively impaired, and other racial and ethnic groups.

	ACKNOWLEDGMENTS

 
The authors thank Cheryl Bibbs and Pam Aye-Simon for study coordination, Pam Aye-Simon for her technical expertise, Wenqing Fan and Woojeong Bang for programming, and all the CHAP interviewers.

	FOOTNOTES

 
¹ Supported in part through funding from National Institute of Aging grants AG11101 and AG13170.

³ Abbreviations used: CHAP, Chicago Health and Aging Project; FFQ, food frequency questionnaire; NCC, Nutrition Coordinating Center.

Manuscript received 12 September 2003. Initial review completed 24 October 2003. Revision accepted 16 December 2003.

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TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 

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