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Journal of the American College of Nutrition, Vol. 24, No. 3, 217-226 (2005)
Published by the American College of Nutrition

Plasma Carotenoid and Vitamins A and E Concentrations in Older African American Women after Wheat Bran Supplementation: Effects of Age, Body Mass and Smoking History

Boyd R. Switzer, PhD, Jan R. Atwood, RN, PhD, FAAN, Aliza H. Stark, PhD, John W. Hatch, DrPH, Rebecca Travis, MPH, RD, Fred Ullrich, BS, Elizabeth R. Lyden, MS, Xiumei Wu, PhD, RN, Yulanda Chiu, PhD, RN and Jan L. Smith, MPH, RN

University of North Carolina at Chapel Hill, North Carolina (B.R.S., A.H.S., J.W.H., R.T., X.W., Y.C., J.L.S.)
University of Nebraska Medical Center at Omaha, Nebraska (J.R.A., F.U., E.R.L.)

Address reprint requests to: Boyd R. Switzer, Ph.D., Dept. of Nutrition, University of North Carolina-Chapel Hill, Chapel Hill, NC 27599-7461. E-mail: boyd_switzer{at}unc.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 CONCLUSIONS
 ACKNOWLEDGMENTS
 REFERENCES
 
Objective: This study investigated the relationships of plasma vitamins A, E, and carotenoids with age, BMI and former/non-smoking history after adjusting for wheat bran supplementation.

Methods: All 39 African American women in the church-based, volunteer sample, 40–70 years old, supplemented their daily diets for 5–6 wks. with 1/2 cup of a riboflavin-spiked wheat bran cereal.

Results: Urinary riboflavin concentrations increased from 0.8 ± 0.1 mg/day at baseline to 7.5 ± 0.5 mg/day after supplementation, confirming the 99.2 ± 10.5% self-reported adherence. Plasma nutrient concentrations did not change significantly with supplementation nor was never/former smoking history related to diet. Plasma retinol and serum cholesterol were significantly higher (p < 0.0002) in persons older than 55 years compared to younger adults. Plasma retinol (µg/dL) but not serum cholesterol was associated significantly with menopausal status and hormone replacement therapy (HRT; p = 0.05); progressive increases in retinol concentrations were found in the women after adjusting for pre/post supplementation: lowest in pre-menopause (47.7 ± 4.8); intermediate concentrations in post-menopause on HRT (54.6 ± 3.0); highest level in post-menopause without HRT (61.1 ± 3.0). Similarly, a progressive increase was found in lipid-unadjusted {alpha}-tocopherol concentrations and menopausal status with or without HRT. Vitamin A and cholesterol intakes were not significantly different by age group. Plasma carotenoids were not significantly different by age or fiber supplementation, but {alpha}- and ß-carotene and ß-cryptoxanthin were significantly lower with BMI ≥ 30. In contrast to carotenoids, both plasma levels of {gamma}-tocopherol and lipid-adjusted {gamma}-tocopherol were significantly higher with obesity compared to those with BMI < 30.

Conclusion: Plasma {alpha}- and ß-carotene and ß-cryptoxanthin were negatively associated with obesity, whereas {gamma}-tocopherol measures were consistently elevated with high BMI. The increase in age-associated plasma retinol in postmenopausal women was likely related to decreased estrogen concentrations in the African American women. Smoking history was not influential in this study.

Key words: African American, women, vitamin A, vitamin E, age, BMI

Abbreviations: BMI = body mass index • HRT = menopausal status/hormone replacement therapy • AFFQ = Arizona Food Frequency Questionnaire • SE = standard error • NHANES III = National Health and Nutrition Examination Survey


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 CONCLUSIONS
 ACKNOWLEDGMENTS
 REFERENCES
 
Diets high in dietary fiber are considered part of a healthy food consumption pattern. Major sources of dietary fiber are whole-grains, fruits, and vegetables. Whole grains and wheat bran, contain predominantly insoluble fiber whereas fruits and vegetables contain predominantly soluble fiber [1]. These two types of dietary fiber provide many physiological benefits, such as a flattening of the peak absorption of postprandial glucose, decreased absorption of cholesterol, binding and dilution of carcinogenic agents from foods, water-holding and bulking of feces to decrease constipation, and a modification of bacterial flora so that fewer harmful mutagenic compounds are produced [2,3]. The effect of a specific type of fiber, such as found in wheat bran, on plasma carotenoids and vitamins A and E has not been carefully studied in humans.

In addition to dietary fiber, age, body mass and smoking are important factors affecting the level of plasma vitamins and antioxidant nutrient status. From ages 14 to 70 years, retinol concentrations steadily increase in men and in women [4]. Higher plasma concentrations of retinol and {alpha}-tocopherol appear to be associated with longevity. For example, healthy centenarians have been shown to have plasma retinol concentrations about 2 fold higher and {alpha}-tocopherol concentrations about 1.3 fold higher than adults ranging between 60 years and 99 years [5].

Serum concentrations of ß-carotene and {alpha}-tocopherol are positively associated with diet and serum cholesterol. In addition, serum ß-carotene concentration is positively associated with dietary fiber in both men and women, whereas it is negatively associated with the amount of tobacco smoked only in men. Serum ß-carotene is negatively associated with obesity in men and women [6].

Epidemiologic evidence reveals that cigarette smokers have significantly lower plasma concentrations of antioxidant nutrients, especially vitamin C, {alpha}-carotene and ß-carotene [7–10]. Alberg et al. [11] observes lower serum concentrations of {alpha}-carotene, ß-carotene, and ß-cryptoxanthin in both current and former active and passive smokers compared with non-smokers; no significant differences are found in retinol, {alpha}- and {gamma}-tocopherol (not lipid-adjusted) and other carotenoids in the same group comparisons. Exposure of human plasma to cigarette smoke in vitro is capable of destroying the carotenoids and tocopherols while retinol appears the most resistant to destruction [12,13]. Although the ethnic backgrounds of the populations were not reported, the ethnicity was most likely white. In addition, the relationship between age and plasma vitamin A has been explored with regard to menopausal status in very few studies and none in African American women, to our knowledge.

Data collected from participants in a Wheat Bran Fiber intervention were used to explore the relationship between age and smoking with plasma vitamins A, E, carotenoids and cholesterol. This study of older, African American women adds new data on dietary and plasma concentrations of carotenoids and other nutrients that have been reported previously for primarily white, non-Hispanic populations. Our study clarifies the relationship of plasma retinol concentrations and cholesterol that is confounded by age. This research also enhances our understanding of the linkage between plasma retinol concentrations and menopausal status with or without hormone replacement therapy (HRT). Age and hormone status must be considered when interpreting plasma concentrations of retinol.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 CONCLUSIONS
 ACKNOWLEDGMENTS
 REFERENCES
 
Study Population and Design
Eligible subjects were 39 healthy African American women, aged 40–70 years, recruited from members and friends of churches in Durham, NC. Eligibility was determined at baseline on the basis of the absence of serious co-morbidities (e.g., non-insulin-dependent diabetes) and adequate nutritional status (e.g., dietary intake within normal ranges). All participants gave informed consent according to federal and University of North Carolina Human Subjects Committee guidelines. Participants enrolled in the NIH-funded project "Fiber Adherence and Marker Development in Black Churches", completed a general physical examination, dietary intake assessment, medical questionnaire, and instruction on collection of 24-hour urine specimens. Individuals consuming greater than 30 g/day of dietary fiber at baseline were excluded from the intervention because they could not likely benefit from the fiber intervention. These high fiber consumers were included, however, in the educational sessions. Participants averaged 57.4 ± 1.4 years of age, (mean ± se), 49% (n = 19) were married, and on average were well educated (14.4 ± 0.3 years). Ten percent (n = 4) had household incomes under $20,000 (median income $40,000) and 56% were still employed and not retired (Table 1).


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  		Table 1. Descriptive Characteristics of the African American Womena

 
A correlational descriptive design was used in this community-based study. After collecting baseline dietary, medical, urine and blood samples, all participants did a one to two week run-in period to work up to a full dose of fiber (35 g of wheat bran cereal containing 11.6 g of dietary fiber and 28 mg of riboflavin marker). Participants made weekly visits to the study site to receive education on better eating habits, their weekly fiber supplement and to report their previous week’s supplement consumption with the goal of adherence levels of 75% or better [14,15]. After successful completion of five to six weeks in the study depending on weather, vacations and clinic schedules, post-intervention dietary intake, anthropometric measures, blood, and urine samples were collected. Self-reported adherence level was 99.2 ± 10.5% [16]. Urinary riboflavin concentrations increased from 0.8 ± 0.1 mg/day (mean ± se) at baseline to 7.5 ± 0.5 mg/day after supplementation, validating the high self-reported adherence (p < 0.0001) (Table 2 footnote g). In a previous dose-response clinical research study [17], urinary riboflavin excretion was highly correlated with the dose of wheat bran supplement intake (r = 0.96, p < 0.001).


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  		Table 2. Plasma Concentration of Metabolites by Age Group, Pre- and Post-interventiona

 
Dietary Assessment
Nutrient intake was assessed via the 1990 computer scannable version of the Arizona Food Frequency Questionnaire [18], both pre and post wheat bran intervention. The AFFQ is a self-report questionnaire, eliciting responses to both how often a food is eaten and what serving size is consumed, tapping over 100 food descriptors, plus validity checks on each food group. The range of foods was expanded from the Block [19] Questionnaire to be suitable to Southwestern US diets [18] and well tested for research use [20]. Estimates of energy intake from the AFFQ were validated recently with doubly-labeled water [21]. The appropriateness of the food choices was validated specifically for Southern African Americans for this study [16]. In addition, respondents were explicitly instructed to claim grits under the appropriate cereal option, even though grits are often eaten with lunch and dinner rather than with breakfast. Plastic food models of the serving sizes for liquids, cereals, meats and vegetables were in the respondents’ sight during AFFQ completion. They completed the questionnaire only after receiving a short training session to promote accuracy of reporting. In addition to food frequency, the AFFQ queries fat sources (e.g., chicken with skin, kinds of fat used), vitamin and mineral intake, special diet usage, weight change, and smoking behavior (never, previous smoker, how much currently smoked). The forms were double-checked for completeness before being sent to the University of Arizona Cancer Center for data entry and food analysis. Double-entry scanning to 100% accuracy promoted data entry precision. The food analysis database produced nutrient summaries (Univ. of Arizona), which seemed accurate when cross-checked with the data collectors.

Sample Collection, Storage and Laboratory Analyses
After an overnight fast of 12 hours, two blood samples, one for plasma and one for serum, were collected in the University of North Carolina Clinical Research Center and then transported within an hour of collection to the laboratory at 4°C. The blood was centrifuged at 200 x g for 15 min at 4°C. The plasma and serum were separated and placed in 2 ml labeled cryostat tubes. The plasma samples were immediately placed in a –20°C freezer and then later transferred to an –80°C freezer. The sera were sent to a standardized clinical laboratory for enzymatic analysis of total cholesterol. The chilled 24-hour collections of urine in brown 2 liter bottles containing 5 ml of glacial acetic acid were transported to the laboratory. The total volume was measured and recorded. Urinary creatinine was measured to confirm completeness of collection, which in some cases required a second 24-hour collection. A portion of the urine was acidified with HCl and stored frozen at –20°C. Urinary riboflavin excretion/day was determined using the method of Chastain & McCormick [22] as previously described [18,23]. For the vitamin and carotenoid measurements, plasma samples were thawed and the determination of retinol, tocopherols and carotenoids was conducted using the HPLC method of Sowell et al. [24]. Purified standards were obtained from the following sources: retinol, {alpha}-tocopherol, {gamma}-tocopherol, lycopene, {alpha}-carotene and ß-carotene from Sigma Chemical Co. (St. Louis, MO); lutein/zeaxanthin and ß-cryptoxanthin from Hoffmann-LaRoche, Inc. (Nutley, NJ). Each plasma sample was spiked with 108 µg of {alpha}-tocopherol acetate as the internal standard and data were adjusted appropriately. Standard reference sera were obtained from the National Institute of Standards and Technology, (Gaithersburg, MD) and external pool control sera were used from the Centers of Disease Control and Prevention, (Atlanta, GA).

Factors for converting plasma and urinary nutrients from weight to molar units are as follows: retinol, x0.03491 µM; {alpha}-tocopherol, x0.02322 µM; {gamma}-tocopherol, x0.024 µM; {alpha}-carotene, ß-carotene & lycopene, x0.01863 µM; lutein, x0.01758 µM; ß-cryptoxanthin, x0.01809 µM; cholesterol, x0.02586 µM; and riboflavin, x2.657 µmoles/day.

Statistical Analyses
All analyses were performed using SAS version 8.2 [25]. A detailed survey of supplement intake was used to adjust the plasma concentrations of {alpha}-tocopherol. Differences among mean values were tested by two-way general linear regression models with and without interaction terms of independent variables with significance set at p < 0.05. When an interaction was found, separate group analyses were performed. When interactions were not present, least-square-mean analyses were conducted to describe the effect of a significant independent variable while adjusting for pre/post intervention. Also, Duncan’s multiple comparison analyses were applied.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
CONCLUSIONS
 ACKNOWLEDGMENTS
 REFERENCES
 
Plasma/Dietary Nutrients by Age and Pre/Post-Treatment
At baseline, women age >55 (n = 24) as compared to those younger (n = 15) had higher mean (± se) plasma retinol (57.9 ± 4.1 vs. 46.6 ± 2.0 µg/dL, Table 2, p = 0.045), {alpha}-tocopherol (1260 ± 110 vs. 980 ± 74 µg/dL, p = 0.039) and total serum cholesterol (224 ± 4 vs. 200 ± 8 mg/dL, p = 0.016) concentrations. However, the {alpha}-tocopherol adjusted for lipid/vitamin supplement was not significantly associated with age group. At post-intervention, retinol concentrations were significantly higher also in persons over 55 years old (65.6 ± 3.4 vs. 47.0 ± 2.4, p = 0.0004). The post-intervention serum cholesterol concentrations of participants in the older group as compared to the younger group were consistently higher in both pre- and post-intervention groups as expected (p = 0.004). After adjusting for pre/post intervention (no significant interaction of intervention with age) and BMI in a separate analysis, plasma retinol (61.7 ± 2.2 vs. 46.6 ± 2.9 µg/dL, p < 0.0001) and serum cholesterol (227 ± 4 vs. 200 ± 6 mg/dL; p < 0.0002; Table 2 footnote b) still tested significantly higher in persons older than 55 years as compared to younger adults. The self-reported, daily cholesterol intake of older participants at pre- and post-intervention (239 ± 30 mg/day and 188 ± 26 mg/day) was not significantly different from that of younger participants (203 ± 17 mg/day and 194 ± 23 mg/day, p = 0.56; data not shown). In a similar manner, the vitamin A intake of older participants at pre- and post-intervention (11470 ± 1355 IU/day and 9045 ± 831 IU/day) was not significantly different from that of younger participants (11606 ± 1082 IU/day and 9696 ± 959 IU/day, p = 0.73).

Menopause/Hormone Status and Plasma Nutrients
The plasma retinol values were significantly associated with menopausal status and hormone replacement therapy (p = 0.05, Table 3, Fig. 1. The lowest plasma retinol values were observed in pre-menopausal women (45.9 µg/dL at post intervention) and the highest values were seen in post-menopausal women without hormone replacement therapy (65.0 µg/dL at post intervention). {alpha}-Tocopherol (unadjusted) showed a similar significant relationship as retinol with menopausal/hormone replacement therapy (HRT). However, when {alpha}-tocopherol was adjusted for lipid/vitamin supplement, this relationship was not significant (Table 3). After adjusting for pre/post intervention in a separate analysis (no significant interaction of intervention with HRT; Table 3 footnote b), plasma retinol (µg/dL) and not serum cholesterol was associated significantly with menopausal status and hormone replacement therapy with a progressive increase in concentrations from the lowest in pre-menopausal women (47.7 ± 4.8 µg/dL) to intermediate concentrations in post-menopausal women on HRT (54.6 ± 3.0 µg/dL) to the highest level in post-menopausal without HRT (61.1 ± 3.0 µg/dL). {alpha}-Tocopherol has a relationship with age and hormone status similar to that of retinol unless the plasma tocopherol concentrations are adjusted for serum cholesterol and vitamin supplement use.


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  		Table 3. Plasma Metabolite Concentrations of Women by Menopausal Status/Hormone Replacement Therapy (HRT) and by Pre/post Interventiona

 


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  		Fig. 1. Mean plasma retinol concentrations (µg/dL) of women by pre/post fiber supplementation and by menopausal status with or without hormone replacement therapy (±HRT; p = 0.05).

 
Plasma Vitamins and Carotenoids by BMI and Smoking History
Plasma {gamma}-tocopherol was significantly associated with obesity when defined as BMI ≥ 30 (Table 2 & 4). After adjusting for pre/post wheat bran intervention and smoking history, higher plasma {gamma}-tocopherol and lipid-adjusted {gamma}-tocopherol levels were positively associated with obesity as compared to those with BMI <30 (Table 4 footnote). Plasma retinol or unadjusted {alpha}-tocopherol concentrations were not associated with BMI. Plasma carotenoids, especially {alpha}-carotene and ß-carotene and ß-cryptoxanthin were inversely and significantly associated with BMI. An inverse trend was found between lutein and BMI. No relationship of plasma lycopene and BMI was observed either when age group or smoking history was included along with pre/post intervention in the regression analyses.


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  		Table 4. Plasma Concentration of Metabolites by Smoking History, Pre- and Post-interventiona

 
With regard to smoking history, there were no significant differences observed by smoking history in plasma carotenoids or vitamins (Table 4). The mean daily nutrient intakes were not significantly different among African Americans by smoking history (never smoked or, former smokers abstinent for >6 months; data not shown). The daily intake of energy, protein, carbohydrate, fat and cholesterol was not significantly different among participants at pre versus post intervention. However, the daily nutrient intakes reported by participants were lower at post- versus pre-intervention [vitamin A (p = 0.04), {alpha}-carotene (p = 0.003), ß-carotene (p = 0.009), and ß-cryptoxanthin (p = 0.007). Lutein intake had an interaction with smoking history by intervention, which required separate group analyses. No significant difference in mean lutein intakes was found between pre- and post-intervention times for non-smokers. Among former smokers, however, lutein intake at post intervention was significantly less than at pre intervention (p = 0.001).

A lower intake of vitamin A and some carotenoids were reported by participants after 5–6 weeks of wheat bran supplementation, which is confirmed by the higher dietary fiber and by the higher riboflavin marker at post intervention in both smoking-history groups (dietary fiber in g/day: 28 ± 2 vs. 18 ± 1 or 27 ± 3 vs. 23 ± 2, p < 0.0001; riboflavin in mg/day: 30.2 ± 0.7 vs. 1.6 ± 0.1 or 29.3 ± 0.1 vs. 1.8 ± 0.2, p < 0.0001). After completing the intervention of wheat bran supplementation, the participants reported decreased intake of carotenoids, which reflected lower consumption of yellow/orange vegetables. Also, all participants reported lower intake of ß-cryptoxanthin, which suggested lower consumption of fruits such as oranges. Only the former smokers reported significantly lower intake of lutein concentrations (p = 0.001), which likely reflected lower consumption of green vegetables.


   DISCUSSION
 
We observed no significant overall change in concentrations of plasma retinol, {alpha}- or {gamma}-tocopherol, carotenoids and serum cholesterol with validated significantly-increased wheat bran supplementation. Also, never/former smoking history was not a significant confounder. Since wheat bran contains mostly insoluble fiber, we did not find a change in serum cholesterol, which is consistent with most research studies [26–28]. Insoluble fiber appears not to change plasma concentrations of retinol in these African American women, which is also consistent with one report [29]. However, previous studies reported that serum vitamin A concentrations were significantly reduced in both normal healthy subjects consuming 40 g unprocessed wheat bran with vitamin A tablet for 3 weeks [30] and non-insulin-dependent diabetics consuming 5 g of guar gum or wheat bran three times per day for 10 months [31]. In contrast, Kasper et al. [32] reported significantly higher areas under serum vitamin A concentration curves in 11 normal women, ages 19–22 years, consuming 15g of either wheat bran, apple pectin or guar flour as compared to the control group taking milk formula without any fiber during a 9-hour postprandial period. The apparent inconsistent reports may be in part due to comparison of different types of dietary fiber and to measurement of total serum vitamin A versus specific molecules, such as retinol and retinyl esters.

Plasma Vitamin A and Age
Concentrations of plasma retinol and serum cholesterol were significantly higher in older participants than younger ones (Table 2), which is consistent with Ballew’s recent findings [4]. Kark et al. observed in 1981 [33] that serum vitamin A was highly correlated with cholesterol in a mostly white southern population. Our findings confirm the results of these two studies [4,34], indicating that serum retinol concentrations are positively associated with age and total cholesterol. Up to age 13 years, retinol concentrations were indistinguishable between U.S. males and females [2813 white or 1524 non-Hispanic black participants in the third National Health and Nutrition Examination Survey (NHANES III, 4)]. After age 13, retinol concentrations of males continued to rise to about 58 µg/dL, whereas retinol concentrations of non-pregnant females remained in the mid to upper 40s µg/dL from age 14 to 50 years. After 51 years of age, the non-pregnant females’ retinol concentrations increased dramatically and approached those observed in males.

The positive relationship reported here of fasting plasma retinol with increasing age may be a separate phenomenon from that of postprandial retinyl esters with age. Krasinski et al. [35] reported that among non-vitamin supplement users, men (116 elderly and 57 young) had nearly the same fasting plasma retinol concentrations, whereas elderly women had significantly lower fasting retinol concentrations than the men. Young women had the lowest fasting retinol concentrations. Fasting retinol concentrations were not related to supplemental vitamin A intake for either gender. However, fasting plasma retinyl ester concentrations were significantly increased with supplement use and the mean level was a significant 1.5-fold higher among elderly as compared to young adults. In another study [36] of 86 healthy men and women, aged 19–76 years, supplemental vitamin A appearing in the plasma as retinyl esters was cleared significantly more slowly in elderly adults than in younger subjects. Thus, from previous studies, elderly men and women cleared retinyl esters carried by chylomicrons from plasma more slowly than younger people on the same dietary sources of vitamin A. Our findings in African-American women extended prior understandings by showing that fasting plasma retinol concentrations rise when estrogen concentrations decrease after menopause and with age (Tables 2 & 3). In women, a separate mechanism affects plasma retinol concentrations. That is, we propose that the higher level of estrogen present in young women or pregnant women either limits the release of retinol with retinol binding protein (RBP) from the liver or increases the uptake of retinol from RBP into tissues. Further research will be needed to determine which mechanism explains our observations. Therefore, age and hormone status must be considered when interpreting plasma concentrations of retinol.

Plasma Vitamin A & E and Hormone Replacement Therapy
The current study also observed that plasma concentrations of {alpha}-tocopherol in African Americans were significantly associated with menopausal status and age. Similarly, Rock et al. [34] reported that plasma {alpha}-tocopherol was significantly related to age, serum cholesterol and dietary intake support, mostly among white Americans. They reported that 62% of the variance of serum {alpha}-tocopherol (lipid-unadjusted) was explained by serum cholesterol, age and dietary {alpha}-tocopherol with serum cholesterol exerting the strongest effect. In our study, the association of {alpha}-tocopherol with age disappeared after adjusting for serum cholesterol and dietary intake (Table 2). However, plasma retinol concentrations were significantly related to the menopausal status/hormone replacement therapy while serum cholesterol did not show any association (Table 3).

Our study (Table 3) suggests that the estrogen concentrations during pre-menopausal years blunt the rise in plasma retinol concentrations by one of the two mechanisms suggested above. Pre-menopausal women younger than 55 years had the lowest plasma retinol concentrations of 46–50 µg/dL, whereas post-menopausal women not on hormone replacement therapy had the highest plasma retinol concentrations of 57–65 µg/dL. High estrogen concentrations in women were associated with suppressed plasma vitamin A, which was supported by observed concentrations of 42 µg/dL in pregnant women at 12–23 weeks of gestation before hemo-dilution had become a major issue [37]. It should be noted that plasma vitamin A decreased dramatically by 36–39 weeks of pregnancy to 25 µg/dL. In a study of middle-aged women in rural China [38], plasma retinol was increased 10% in the first 2 years of menopause (p = 0.028). Recently, a study of 38 menopausal women in Turkey [39] reported that serum vitamin A and lipid-unadjusted vitamin E significantly increased after hormone replacement therapy as compared to measures at baseline. Our findings are consistent with both of these studies. Thus, high estrogen concentrations in women are associated with suppressed plasma retinol concentrations, possibly in a dose related manner.

Vitamin E and Carotenoids with BMI
Our study shows that plasma {alpha}-tocopherol was higher in older versus younger women and after adjustment for cholesterol, there was no age effect. This was similarly reported among French women [40]. Serum {alpha}-tocopherol was negatively associated with BMI in two studies [6,41] and not associated in two other studies [40,42]. In contrast to {alpha}-tocopherol, serum {gamma}-tocopherol was positively associated with BMI in one study [41] other than our study.

Our study shows that plasma {alpha}- and ß-carotene and ß-cryptoxanthin were negatively and significantly associated with BMI ≥ 30, whereas plasma lycopene had no relationship with BMI. At least one study [40] reported that plasma lycopene was inversely correlated (r = –0.38) with BMI, whereas plasma {alpha}- and ß-carotene and ß-cryptoxanthin were not correlated with any anthropometric variable. However, like ours, most other reports [6,41] among females consistently showed serum ß-carotene was negatively associated with BMI and all other measures of obesity.

The high educational level of our participants may help to explain why we did not observe any difference in daily intake of vitamin A and carotenoids between never-smokers and former smokers. Most studies report lower intake of carotenoids, especially ß-carotene, in smokers compared to non-smokers [43–45]. In our study, both groups of non- and former smokers reported significantly lowering their mean intake of vitamin A, {alpha}-carotene, ß-carotene, lutein/zeaxanthin and ß-cryptoxanthin (no change in lycopene) at 6 weeks compared to baseline data collection. This lower post intake of nutrients suggests all of the participants either systematically estimated smaller portion sizes or less frequent consumption of dark green or yellow/orange vegetables and fruits on the second food frequency questionnaire.

Limitations of Study
Statistical relationships of plasma nutrients with age and smoking history were tested to the extent possible with a small sample size of 39 African American women in the church-based study. Our population provided insights into the inter-relationships of fasting retinol, serum cholesterol, estrogens, age and BMI. This study did not permit analyses focusing on current smokers.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 CONCLUSIONS
ACKNOWLEDGMENTS
 REFERENCES
 
This study found that both plasma retinol and serum cholesterol concentrations rose significantly with age (p < 0.001). Among the women in our sample, the rise of plasma retinol with age was associated with menopausal status/hormone replacement therapy (p = 0.05). The highest plasma concentrations of retinol were observed when estrogen concentrations declined in postmenopausal women without hormone replacement therapy. Serum cholesterol concentrations were not associated with menopausal status/hormone replacement therapy. Plasma concentrations of retinol, {alpha}-tocopherol, {gamma}-tocopherol, and carotenoids did not significantly change from baseline in African Americans after wheat bran supplementation for 5–6 weeks. Plasma {gamma}-tocopherol was positively associated with BMI (p ≤ 0.05), whereas plasma {alpha}- and ß-carotene and ß-cryptoxanthin were negatively associated with BMI ≥ 30 (p < 0.05).


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 CONCLUSIONS
 ACKNOWLEDGMENTS
REFERENCES
 
We are indebted to the participants of the Fiber is Fine project staff (Fiber Adherence and Marker Development in Black Churches) for their dedication and informed partnership. We wish to acknowledge Kellogg’s generous provision of the wheat bran supplement spiked with 28 mg of riboflavin/0.5 cup serving. ß-Cryptoxanthin was graciously provided by Hoffmann-LaRoche, Inc. This study was supported in part by NIH, National Institute of Nursing Research, R01 NR03552, NIH GCRCRR00046, by awards from University of NC-Chapel Hill Lineberger Comprehensive Cancer Center, and University of Nebraska Medical Center, College of Nursing and the UNMC/Eppley Cancer Center.

Received December 29, 2002. Accepted December 6, 2004.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 CONCLUSIONS
 ACKNOWLEDGMENTS
 REFERENCES
 

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