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Jean Mayer U.S. Department of Agriculture Human Nutrition Center on Aging at Tufts University, Boston, MA 02111, a Department of Nutritional Sciences, University of Connecticut, Storrs, CT, 06269 and b Framingham Heart Study, Framingham, MA 01702
| ABSTRACT |
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-carotene
0.33 and 0.18, ß-carotene, 0.36 and 0.25; ß-cryptoxanthin, 0.44 and
0.32; lycopene, 0.35 and 0.21; and lutein + zeaxanthin, 0.27 and
0.10, respectively. Adjustment for age, energy intake, body mass index
(BMI, kg/m2), plasma cholesterol concentrations and smoking
reduced the gender differences, respectively, to the following:
-carotene 0.30 and 0.28; ß-carotene, 0.34 and 0.31;
ß-cryptoxanthin, 0.45 and 0.36; lycopene, 0.36 and 0.31; and
lutein + zeaxanthin, 0.24 and 0.14. Plots of adjusted mean plasma
carotenoid concentration by quintile of respective carotenoid intake
show apparent greater responsiveness among women, compared with men, to
dietary intake of
- and ß-carotene and ß-cryptoxanthin, but
similar blood-diet relationships for lycopene and lutein +
zeaxanthin. Reported daily intake of fruits and vegetables correlated
most strongly with plasma ß-cryptoxanthin and ß-carotene among
women and with plasma
- and ß-carotene among men. With the
exception of lutein + zeaxanthin, this dietary questionnaire does
provide reasonable rankings of carotenoid status among elderly
subjects, with the strongest correlations for ß-cryptoxanthin.
Appropriate adjustment of confounders is necessary to clarify these
associations among men.
KEY WORDS: carotenoids dietary questionnaire humans plasma phytochemicals
| INTRODUCTION |
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-carotene, ß-cryptoxanthin, lycopene and lutein + zeaxanthin. Each of these has hypothetical health effects, making its
individual assessment important. The recent negative results of major
ß-carotene supplementation trials, despite a wealth of studies
showing protective effects of higher plasma ß-carotene concentrations
from dietary intake, demonstrate the need to examine other
phytochemicals that may coexist with ß-carotene in the diet
(Hennekens et al. 1996
Several studies have compared the dietary intake measures of carotene
or ß-carotene equivalents with plasma concentrations of carotene or
total plasma carotenoids (Boeing et al. 1997
, Jacques et al. 1993
,
Jarvinen et al. 1993
, Liu et al. 1992
, Roidt et al. 1988
, Stryker et al. 1988
, Willett et al. 1983
). One report has related general carotene
intake with individual plasma carotenoids (Bingham et al. 1997
); more
recently, several studies have compared the intakes of individual
carotenoids with their respective plasma concentrations (Brady et al. 1996
, Coates et al. 1991
, Forman et al. 1993
, Michaud et al. 1998
, Peng et al. 1995
, Ritenbaugh et al. 1996
Scott et al. 1996
, Yong et al. 1994
). Six of these measured dietary intake of carotenoids with
modified versions of the Block food-frequency questionnaire (Brady et al. 1996
, Coates et al. 1991
, Forman et al. 1993
, Peng et al. 1995
,
Ritenbaugh et al. 1996
, Yong et al. 1994
), and three used diet records
(Forman et al. 1993
, Scott et al. 1996
, Yong et al. 1994
). We are aware
of only one study that used the Willett food-frequency questionnaire
(Michaud et al. 1998
). In this study, we examine the relationship
between intake of individual carotenoids, as measured with the Willett
126-item food-frequency questionnaire (Rimm et al. 1992
, Willett et al. 1987
), and plasma concentrations in a sample of 201 men and 346 women,
aged 6793 y, participating in the Framingham Heart Study.
| METHODS |
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The Framingham Heart Study is a longitudinal cohort study that was
initiated in 1948 to examine risk factors for heart disease.
Approximately 5200 men and women were examined at baseline (Dawber et al. 1951
). At the 20th examination (198889), more than half of the
original cohort had died; 1401 subjects were examined. Of these, a
total of 230 men, aged 6891 y, and 408 women, aged 6793 y, without
diagnosed cardiovascular disease, cerebrovascular disease or cancer
were selected for analysis of plasma carotenoids. These individuals
were selected to avoid potential confounding due to the possible
effects of these chronic diseases on nutrient metabolism. Completed,
usable food-frequency questionnaires were available for 201 men and 346
women; these comprise the sample used here.
Dietary measures.
Usual dietary intake was assessed at the 20th examination with a
semiquantitative 126-item food-frequency questionnaire (Rimm et al. 1992
, Willett et al. 1987
). Questionnaires were mailed to the subjects
before the examination, and they were asked to complete them and bring
them to the exam. This questionnaire instructs subjects to complete
frequency of consumption of individual foods, with the assumption of a
standard portion size, which is provided on the questionnaire for
guidance. For fruits and vegetables, these are usually either one
piece, one-half cup or a small glass of juice. The questionnaire also
includes questions about use of vitamin and mineral supplements and
allows specification of the type of breakfast cereal most frequently
used. This food-frequency questionnaire has been validated for many
nutrients including dietary carotene, and in several populations
against multiple diet records and/or plasma measures, (Ascherio et al. 1992
, Jacques et al. 1993
, Willett et al. 1983
). We know of only one
study that has examined the validity of this questionnaire for
individual carotenoids (Michaud et al. 1998
). Questionnaires resulting
in energy intakes <2.51 or >16.74 MJ (600 and 4000 kcal,
respectively) per day, or with >12 food items left blank were
considered invalid and excluded from further analysis. Of 1068 food
frequencies, 92 (8.6%) were eliminated on the basis of these criteria.
Individual carotenoid intakes were calculated at Harvard University
with a carotenoid database developed for the questionnaire from the
USDA carotenoid database (Mangels et al. 1993
). Reported frequency of
individual fruit and vegetable items were standardized to daily intake
and summed to obtain the average number of reported servings of fruits
and vegetables consumed per day for each person.
Plasma measures.
The methodology for assessing the plasma carotenoids has been described
(Vogel et al. 1997
). Briefly, blood samples were collected from
nonfasting subjects during the 20th examination into vacutainer tubes
containing EDTA (1.5 g/L final concentration); plasma was separated
after centrifugation of blood at 1000 x g for 20 min
at 4°C. Plasma aliquots were stored at -80°C. Carotenoid
concentrations were measured with a reversed-phase HPLC method
described by Barua et al. (1993)
, using ß-apo-8'-carotenyl-myristate
in methanol as an internal standard. The HPLC system included a Model
717 autosampler (Millipore, Milford, MA), and carotenoid data were
monitored with a Varian 2550 detector (Palo Alto, CA), set at 450 nm.
The analyte peaks were identified by retention times and quantified
using standard curves of external standards (Sigma Chemical, St. Louis,
MO) for each analyte.
Total cholesterol and HDL cholesterol were measured in fresh plasma at
the laboratory of the Framingham Heart Study using Abbott cholesterol
reagent and an ABA-200 analyzer (Abbott Diagnostics, Irving, TX)
(McNamara and Schaefer 1987
). Non-HDL cholesterol was calculated as the
difference between total cholesterol and HDL cholesterol.
Statistical analysis.
All statistical analyses were performed using SAS (release 6.12, SAS
Institute, Cary, NC) on a VAX mainframe computer. Descriptive means are
presented in the untransformed scale. Neither the dietary nor the
plasma carotenoid measures were normally distributed, and both sets of
variables were normalized using square-root transformations.
Transformed variables were used for all correlational analyses. We used
Pearson correlations to estimate associations between the dietary and
plasma measures for each carotenoid for men and women separately. For
ß-carotene only, correlations were also estimated for the subset of
subjects not using supplements containing ß-carotene (there were no
supplement users for the other carotenoids). Partial correlations were
used to adjust first for age and total energy intake and then also for
body mass index (BMI), plasma cholesterol concentrations, and smoking
for men and women, respectively. Because intake of most nutrients and
other food constituents correlates with energy intake, adjustment for
this variable allows an assessment of the correlation independent of
sample variation in total energy intake, partially adjusting for
differences in intake that may be due to body size or activity levels,
and for some of the measurement error inherent in the questionnaire
(Willett and Stampfer 1986
). Other adjustment variables have been
previously shown to relate to plasma carotenoid concentrations in this
population (Vogel et al. 1997
).
To estimate the relationship between total number of fruits and vegetables reported as servings consumed per day and each of the carotenoids, we used Pearson correlations to compare the distribution of each plasma carotenoid (square-root transformed for normality) with total number of servings of fruits, vegetables, and combined fruits and vegetables (also square-root transformed for normality). Both the crude and adjusted correlations (as described above) were calculated.
We estimated mean plasma carotenoid concentrations for respective intake quintiles, for women and for men, using the General Linear Models (GLM) procedure, with adjustment for age, energy intake, BMI, plasma HDL and non-HDL cholesterol concentrations, and smoking. These mean values were then plotted along with their 95% confidence intervals, separately for men and women. Finally, we identified and ranked the major food contributors to the intake of each carotenoid.
| RESULTS |
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-carotene, ß-carotene and ß-cryptoxanthin than did the men. Men
had slightly higher lycopene concentrations, although neither these nor
the lutein + zeaxanthin concentrations differed significantly
across gender. In a similar pattern, women reported higher intakes than
did men, for each of the carotenoids, with the exception of lycopene.
They also reported consumption of more total fruits and vegetables than
did men (an average of 5.1 servings per day vs. 4.4).
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and ß-carotene and lutein + zeaxanthin. For men, however,
adjustment for these variables resulted in relatively large increases
in the correlations, particularly for
- and ß-carotene, which
increased from 0.18 to 0.28 and 0.25 to 0.31, respectively, and for
lycopene, which increased from 0.21 to 0.31.
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- and
ß-carotene were more similar across gender, ranging from 0.23 to 0.27
for adjusted values. Correlations between carotenoid concentrations and
fruit intake and vegetable intake, separately, were generally weaker
than with the combined fruit and vegetable intake variable (data not
shown). The only exception was for ß-cryptoxanthin, for which the
crude and fully adjusted correlations with fruit intake alone were 0.34
and 0.36 for women and 0.20 and 0.24 for men, respectively.
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- and ß-carotene, men tended to have
lower intakes, but in addition, for given intake levels, they appeared
to have lower plasma concentrations, particularly for ß-carotene. The
association between diet and plasma appeared to level off at the higher
intake range for
-carotene, but continued a linear trend throughout
the intake range presented here for ß-carotene.
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-carotene, there
appeared to be a plateau in the plasma response at the highest intake
levels.
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-carotene was obtained from carrots, including the
carrots in mixed vegetables. Although still led by carrots (37%),
sources of ß-carotene were more diverse, and included cantaloupe
(9%), spinach (8%) and sweet potatoes (7%). Intake of
ß-cryptoxanthin was overwhelmingly from orange juice and oranges
(79%), with an additional 14% from peaches. Lycopene was also a
predominantly one-food carotenoid, with more than 80% from tomatoes or
tomato products. Lutein + zeaxanthin had more diverse sources, but
>43% (53% if broccoli is included) came from green leafy vegetables,
mainly spinach.
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| DISCUSSION |
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At least six studies have examined individual associations between
dietary carotenoids, as measured by the Block food-frequency
questionnaire, and plasma carotenoid concentrations (Brady et al. 1996
,
Coates et al. 1991
, Forman et al. 1993
, Peng et al. 1995
, Ritenbaugh et al. 1996
, Yong et al. 1994
). The earliest of these studies used a
database developed specifically for the Block questionnaire, based on
limited analytic data and extrapolation of values for similar foods
(Coates et al. 1991
). The more recent studies have used the database
developed by the USDA and the National Cancer Institute (Mangels et al. 1993
). These databases have been compared and shown to yield different
quantitative estimates, but similar correlations with blood
concentrations (Ritenbaugh et al. 1996
, Vandenlangenberg et al. 1996
).
Correlations reported by these studies range from 0.240.51 for
-carotene; 0.210.58 for ß-carotene; 0.360.46 for
ß-cryptoxanthin; 00.37 for lycopene; and 0.090.45 for
lutein + zeaxanthin. Our findings for each of these carotenoids
fall within these ranges and are higher than those reported by most of
these studies for lycopene and ß-cryptoxanthin, but lower for
lutein + zeaxanthin.
We were able to identify only one study that has examined the
association between individual carotenoid intakes, as measured by the
Willett food-frequency questionnaire, and corresponding plasma
carotenoid concentrations (Michaud et al. 1998
). Looking only at
nonsmokers, Michaud et al. (1998)
reported higher correlations for
-carotene than those reported here for both men and women (0.47 vs.
our 0.28 for men, and 0.48 vs. our 0.30 for women). Among men, their
correlations were higher than those seen here for ß-cryptoxanthin
(0.43 vs. our 0.36), lycopene (0.47 vs. our 0.31) and lutein (0.40 vs.
our 0.14). Conversely, our correlations for ß-cryptoxanthin and
lycopene were higher for women than theirs (0.45 vs. 0.32 and 0.36 vs.
0.21, respectively).
Other studies have compared intake of total carotenoids from the
Willett questionnaire to plasma carotenoid concentrations. Willett et al. (1983)
reported a correlation of 0.29 for this association, which
increased to 0.35 when fully adjusted for age, gender, energy intake
and blood lipid concentrations. Jacques et al. (1993)
found that this
association was much stronger for women (r = 0.49,
P < 0.001) than for men (r = 0.19, not
significant). In this study, we also found higher unadjusted
correlations among women than among men for
-carotene (0.33 vs. 0.18
for women and men, respectively), and ß-carotene (0.36 vs. 0.25).
However, the gender differences closed considerably with adjustment for
total energy intake, age, BMI, plasma cholesterol concentrations and
smoking status. This suggests that the carotenoid diet-plasma
association is confounded by one or more of these variables and that
they should be adjusted in studies that examine these associations.
Willett et al. (1983)
found a significant negative association between
BMI and plasma carotene concentration and a significant positive
association between plasma cholesterol and plasma carotene
concentration (smoking was not included in that study). Several others
(Albanes et al. 1997
, Marangon et al. 1998
, Pamuk et al. 1994
)
demonstrated the negative effect of smoking on plasma carotene
concentrations. We have shown previously (Vogel et al. 1997
) that BMI
was negatively associated with of all the individual carotenoid
concentrations except for lycopene in this sample, and that smoking was
negatively associated with
- and ß-carotene and ß-cryptoxanthin
concentrations, but not with lycopene and lutein + zeaxanthin.
We found that correlations were greatest for ß-cryptoxanthin, which
is found primarily in only a few foods, mainly orange juice and oranges
(79%) and peaches (14%). This was followed by lycopene, found mostly
in tomatoes and tomato products (81%). Correlations were also
reasonably high for
- and ß-carotene, both found mainly in carrots
(77 and 37%, respectively). Correlations were lowest (and not even
significant for the male subset) for lutein + zeaxanthin, which is
found primarily in green leafy vegetables, but with significant
contributions from a much wider variety of foods. Although not
completely consistent, the other studies that have examined these have
tended to report greater correlations for ß-cryptoxanthin and/or
-
and ß-carotene than for lycopene or lutein (Brady et al. 1996
, Coates et al. 1991
, Forman et al. 1993
, Michaud et al. 1998
, Peng et al. 1995
,
Ritenbaugh et al. 1996
, Yong et al. 1994
). The ability of the
questionnaire to capture intake with a few well-defined food items
reduces error of estimate and associated misclassification of dietary
intake. In addition to limitations of the questionnaire, these
differences in correlation strength may be due to several factors,
including the day-to-day variability of the plasma measure of the
nutrient, or issues related to the bioavailability of individual
carotenoids.
The differences across men and women are important and suggest that the
questionnaire performs better among women for these carotenoids. Men
may report their fruit and vegetable intake less accurately than do
women. However, the observation that men generally have lower plasma
concentrations than women of
- and ß-carotene and
ß-cryptoxanthin, but not of lycopene or lutein + zeaxanthin for
the same level of dietary intake, along with the large improvement in
the men's correlations seen with adjustment for BMI, cholesterol
concentrations and smoking, suggest that other mechanisms may be
operating.
Correlations between fruit and vegetable intake and plasma carotenoids
were, not surprisingly, lower than those comparing individual
carotenoid intake with respective plasma concentrations. However, for
- and ß-carotene in both men and women, and for ß-cryptoxanthin
in women, simply measuring total fruit and vegetable intake appears to
provide a reasonable ranking, with correlations ranging from 0.23 to
0.34. On the other hand, fruit and vegetable intake does not appear to
adequately serve as an indicator of lycopene or lutein +
zeaxanthin intake. Further exploration of specific food intakes,
particularly of tomatoes, may prove to be more useful for lycopene
intake. Few studies have compared fruit and vegetable intake directly
with individual plasma carotenoid concentrations. For each of the
carotenoids (except for lycopene for which their correlation was
negative), Polsinelli et al. (1998)
found higher correlations than
those seen in our study. Their correlations, with just 20 adult women,
ranged from 0.31 for ß-cryptoxanthin to 0.73 for
-carotene.
However, they were comparing 7-d food records with blood that was drawn
immediately after the record days. Similar to our results, they found
that combined fruit and vegetable intake yielded the highest
correlations, compared with intake of either fruits or vegetables
alone, except for ß-cryptoxanthin, which is stronger when compared
with fruit intake alone.
In conclusion, correlations for lutein + zeaxanthin suggest that the Willett 126-item questionnaire does not provide a reliable estimate of lutein + zeaxanthin status. Further work to either improve specification of foods containing these carotenoids or in understanding the reasons for the low correlation is needed. On the other hand, this questionnaire does appear to provide reasonably valid and useful information about other individual carotenoids, particularly ß-cryptoxanthin, lycopene and ß-carotene.
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| FOOTNOTES |
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1 Supported in part by federal funds from the U.S.
Department of Agriculture under contract number 533K065-10, the
National Institutes of Health grant number R01 AR/AG 41398, NIH/NHLBI
contract number NO1-HC-38038, and by the Storrs Agricultural Experiment
Station. ![]()
2 The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked ''advertisement'' in accordance with 18 USC section 1734 solely to indicate this fact. ![]()
3 Current address: Department of Medicine, College
of Physicians and Surgeons of Columbia University, New York, NY. ![]()
Manuscript received August 5, 1998. Initial review completed September 4, 1998. Revision accepted October 22, 1998.
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