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2
Departments of
*
Nutrition and
Epidemiology, Harvard School of Public Health, Boston, MA 02115 and
**
Harvard Institute for International Development, Cambridge, MA
2To whom correspondence should be addressed.
| ABSTRACT |
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KEY WORDS: vitamin A tomato children diarrhea respiratory infection Sudan
| INTRODUCTION |
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Although the role of dietary factors in chronic diseases has been
extensively examined in the past few years, much less is known about
their contribution to infectious diseases. In numerous studies, the
consumption of fruits and vegetables was associated with a reduced
occurrence of cancer and cardiovascular disease (Willett 1994
). The consumption of tomatoes, tomato sauce and pizza was
associated with a reduced risk of prostate cancer among men in the
United States (Giovannucci et al. 1995
). In a study from
Italy, the consumption of raw tomatoes was inversely associated with
the occurrence of digestive tract cancers (Francheschi et al. 1994
). In a recent review of the literature, 72 studies
examined the intake of tomatoes, tomato-based products and lycopene
in relation to cancer at various anatomic sites, with a majority
reporting protective associations (Giovannucci 1999
).
The presumed protective effect of fruits and vegetables, including
tomatoes, may be due to their high concentration of antioxidants.
Antioxidants may counteract the adverse effects of oxidative stress and
lead to improved immune function and reduced risk of infectious disease
(Bendich 1988
, Khaled 1994
). Free
radicals are products of the inflammatory response to infections, can
damage healthy cells in the process of fighting pathogens and have been
proposed as important in the pathogenesis of malaria among other
infections (Levander and Ager 1995
) and malnutrition
(Golden and Ramdath 1987
). Antioxidant nutrients,
including lycopene and other carotenoids, neutralize the adverse
effects of these molecules. Hence the balance between free radicals and
antioxidants is important for maintaining healthy body systems,
including the immune system.
Tomatoes are fruits that are rich in lycopene, an antioxidant with
immunostimulatory properties, and contain moderate amounts of
- and
ß-carotene and vitamin C. In a recent study among healthy men, a 2-wk
low carotenoid diet was associated with a significant decrease in
immune function (Watzl et al. 1999
). However, 2 wk of
ingestion of tomato juice resulted in a significant increase in
lycopene levels, as well an increase in T-lymphocyte function, as
measured by mitogen-stimulated lymphocyte proliferation and
interleukin-2 production. In another study (Periquet et al. 1995
), human immunodeficiency viruspositive children had
significantly lower plasma lycopene levels compared with healthy
controls; among positive children, lycopene levels were significantly
correlated with CD4 cell counts (correlation coefficient = 0.57,
P < 0.001). Plasma lycopene levels were also
significantly low in malnourished children from Morocco
(Houssaini et al. 1997
) and Nigeria (Becker et al. 1994
). Other antioxidants found in tomatoes have also been
related to immune function in numerous human and animal studies
(Bendich 1988
).
In this report, we prospectively examined the relationship between the consumption of tomatoes and mortality and diarrheal and respiratory morbidity rates among children in the Sudan.
| MATERIALS AND METHODS |
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After enrollment (round 1), each household was visited every 6 mo for a maximum of three visits (rounds 24). Follow-up rates were 92% at round 2, 87% at round 3 and 84% at round 4. All children available at the last round received 200,000 IU of vitamin A. Children who had evidence of xerophthalmia (night blindness assessed by questioning the mother, Bitots spots, corneal ulcers or corneal scars) at any round were given vitamin A capsules (200,000 IU) and dropped from further follow-up.
Deaths were ascertained from the mother or relatives at a follow-up visit. Children who were not available at home at the time of a visit were not followed further, but their survival status was assessed at that round and at subsequent rounds by questioning relatives and neighbors; in this way, we were able to determine the survival status of 99.5% of all children. Information was obtained about any illness in the week preceding death; mothers were asked about which signs occurred in the period preceding death: diarrhea, breathlessness, fever, rash or convulsions.
We assessed morbidity status at each round by asking the mother
whether, in the preceding 7 d, the child had diarrhea (three or
more loose or watery motions in a 24-h period), cough (lasting
24 h),
fever or measles. We grouped these signs as the following six mutually
exclusive end points: diarrhea alone, diarrhea with fever, cough alone,
cough with fever and/or diarrhea, fever alone and measles regardless of
signs associated with it.
Information on potential risk factors for death was collected at
baseline, including household wealth as assessed by the interviewers on
a four-point scale, availability of water in the house, maternal
literacy and region of residence. We found that each of the latter
three variables was highly correlated with household wealth and
therefore used the four variables as indicators of socioeconomic
status. At each round, the anthropometers measured each childs height
and weight. We assessed the nutritional status of a child at a
particular round using the CASP anthropometric software developed by
the U.S. Centers for Disease Control and Prevention (Hamill et al. 1977
). We considered as abnormal all values below -2
Z scores of the reference value of weight-for-height or
height-for-age.
Tomato consumption, either raw or as part of a cooked meal, was assessed at each round as part of a dietary questionnaire that was administered to mothers. This entailed recalling whether a child had consumed each of a list of vitamin Acontaining foods in the previous 24 h. In this report, events (death or complications) reported at round 2 were allocated according to the tomato intake at round 1, whereas events reported at rounds 3 and 4 were allocated according to the number of days that tomato was eaten in the first two and the first three rounds, respectively. The occurrence of an event among children who ate tomatoes on 1, 2 or 3 d of assessment was compared with that among children who did not consume tomatoes on any of the 3 d. A test for trend in the relationship between intake and mortality or morbidity rates over an increasing number of days was computed by modeling intake as a continuous variable.
Children who were lost to follow-up or who were excluded from further follow-up because they developed xerophthalmia were considered censored for the remainder of the study because their dietary exposure status was not available for the rounds after their exclusion from the study. Thus, each child who did not have xerophthalmia at the beginn-ing of a round and who received a trial capsule contributed one child-period, a period of 6 mo. We considered each child to be a new observation conditional on having survived to the beginning of the next round and updated the exposure variables accordingly.
Incident rates for a given exposure were calculated by dividing the number of events by the cumulated child-periods of follow up. The relative risk of mortality was computed as the rate among children in a certain number of days of tomato intake relative to the lowest category (0 d). Multivariate logistic regression was used to estimate relative risks and 95% confidence intervals (CIs)3 . We adjusted for age, sex, capsule and socioeconomic variables. In separate models, we also adjusted for nutritional and morbidity status in the previous round and used the calendar month of each visit to control for seasonality. A P-value of <0.05 was used to denote statistical significance. Data were analyzed using Statistical Analysis System (SAS) Version 6.12.
The study was approved by the Committee on the Use of Human Subjects in Research of the Harvard School of Public Health, the Director General of Primary Health Care of the Ministry of Health in the Sudan and both Directors of Health for Khartoum and Central Regions.
| RESULTS |
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1 d were at an
increasingly reduced risk of death (P for trend < 0.0001) (Table 2
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To examine the relationship between child mortality rates and tomato consumption independent of its vitamin A content, we added total dietary vitamin A intake to the multivariate model that also included age, sex and socioeconomic variables. The association between tomato use and death remained significant (P for trend = 0.004), although the measures of association were attenuated: compared with children who did not consume tomatoes on any of the 3 d, those who consumed tomatoes for 1 d had a relative risk of 0.64 for death (95% CI, 0.440.92), those who consumed tomatoes for 2 d had a relative risk of 0.61 (95% CI, 0.341.08), and children who consumed tomatoes for all 3 d had a multivariate relative risk of 0.21 (95% CI, 0.050.89).
We also calculated a partial score of caloric intake from the same list of foods in this study. As expected, tomato intake was significantly associated with energy intake. However, on further adjustment for this caloric score, the association between tomatoes and death was only slightly attenuated. Energy intake per se was not associated with death (P = 0.69).
Of 232 deaths, there were 101 (43.5%) associated with diarrhea in the
week preceding death, 63 (27.2%) associated with fever and 23 (9.9%)
associated with difficulty in breathing; the remainder were due to
other causes, including body rashes, convulsions and accidents. We
examined the relationship between the number of days of tomato intake
(modeled as a continuous variable) and cause-specific death. With
each additional day that a child consumed tomatoes,
diarrhea-related mortality rates were reduced by
45%, with
adjustment for age, sex and socioeconomic variables (0.55; 0.350.86;
P = 0.009). Tomato intake was also associated with a
reduced risk of death associated with fever (multivariate relative risk
= 0.65; 0.440.97; P = 0.04) but was not related
to death associated with difficulty in breathing.
The intake of tomatoes was also inversely associated with the
occurrence of diarrhea, and an even stronger relationship with the risk
of diarrhea with fever was noted (multivariate P for trend
for both <0.0001) (Table 3
). Compared with children who did not consume tomatoes at all, those who
ate tomatoes on all 3 d were at a 17% reduced risk of diarrhea
alone (multivariate relative risk = 0.83; 95% CI, 0.710.97) and
a 50% reduction in the risk of diarrhea with fever (0.50; 0.330.86).
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When we added total vitamin A intake to each of the above multivariate models, the intake of tomatoes was still significantly associated with the risks of diarrhea alone (P < 0.0001), diarrhea with fever (P < 0.0001), cough with fever (P < 0.0001) and measles (P = 0.05) but also with increased occurrence of cough (P < 0.0001). The relative risks were slightly attenuated compared with the results that were not adjusted for vitamin A intake. For example, compared with children who did not consume tomatoes on any of the 3 d of assessment, those who consumed tomatoes on all 3 d were 0.52 times as likely to have diarrhea with fever (95% CI, 0.340.79) and 0.54 times as likely to have cough with fever (95% CI, 0.430.68).
| DISCUSSION |
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In the same study population, we previously reported that total dietary
vitamin intake was associated with large and significant reductions in
child mortality rates (Fawzi et al. 1994
) and diarrheal
and respiratory infections (Fawzi et al. 1994
). We also
examined the relationships between these end points and the consumption
of six foods (other than tomatoes) that were selected because they
contributed 97% of the between-person variability in total vitamin
A intake. Protective relationships were noted with the following four
plant sources of vitamin A: Jews mallow, garden rocket (both green
leafy vegetables), mango and pumpkin. The two foods of animal origin
(eggs and fresh milk) were not related to any of the outcomes. The
relationships with Jews mallow and garden rocket were particularly
significant: the multivariate relative risk per day of use of Jews
mallow was 0.32 (1.140.72), whereas for garden rocket, it was 0.58
(0.350.96) (Fawzi et al. 1994
). However, when we
adjusted the relationships between tomato intake and child mortality
rates for these two foods simultaneously, the associations were only
slightly attenuated and remained significant, suggesting that the
findings for tomato are independent of the intake of the other foods.
These results also did not differ with further adjustment for caloric
score. As reported earlier, energy intake itself was not associated
with death. This is not unexpected because the study population was not
severely undernourished and energy intake probably was not a limiting
nutrient. Finally, as in all observational dietary studies, tomato
intake may be a proxy for vegetable intake overall; hence, the
protective relationships observed in this study may be an indicator of
a healthy food pattern (that includes relatively high amounts of
vegetables and fruits) and not necessarily be due to tomato intake per
se.
Tomato intake was associated with a reduction in the risk of severe
diarrhea as shown by the reduced occurrence of diarrhea-related
deaths and diarrheal morbidity among children in the higher categories
of intake. The vitamin A content of tomatoes may explain, at least in
part, the protective associations with tomato intake. Tomatoes contain
moderate amounts of provitamin A carotenoids, mainly
- and
ß-carotene (Beecher 1998
). In several large trials,
vitamin A supplementation resulted in significant reductions in
mortality rates associated with fatal and (presumably severe) diarrhea
(Beaton et al. 1993
; Fawzi et al. 1993
).
Vitamin A supplementation was also associated with a reduction in the
duration (or severity) of diarrheal episodes among hospitalized
patients with measles (Beaton et al. 1993
). Vitamin A
deficiency may contribute to gastrointestinal infection in a number of
ways. It adversely affects the epithelial lining of the
gastrointestinal tract (Wolbach and Howe 1925
), leading
to decreased mucus secretion and weakened local barriers to infection.
In comparison with normal mice, vitamin Adeficient mice had more
severe mucosal changes when infected with rotavirus (Ahmed et al. 1990
), which is an important cause of diarrhea in children.
Vitamin A deficiency also adversely affects humoral and cellular immune
functions (Nauss 1986
).
We also found that children who consumed more tomatoes were more likely
to present with cough. The occurrence of cough may indicate a more
competent respiratory epithelium. Tomato consumption was inversely
related to the risk of "cough with fever." In several
placebo-controlled trials, however, large doses of vitamin A were
not associated with a reduction in the severity of respiratory
infection (Fawzi et al. 1998
; Kjolhede et al. 1995
), suggesting that the observed protective relationship
with tomato intake may be attributed to nutrients in tomatoes other
than vitamin A. Tomato intake was also associated with a reduced risk
of measles, similar to findings for total dietary vitamin A with this
end point (Fawzi et al. 1995
). Because all study
children are likely to have acquired the measles virus at some point in
time, the reduced incidence of measles we report here probably
represents reduced severity of the disease. These findings are in
accord with a reduction in the risk of measles-related mortality
rates associated with periodic vitamin A supplementation in community
trials carried out among healthy children who were hospitalized
with measles (Beaton et al. 1993
; Fawzi et al. 1993
). Although our results were not controlled for the
possible confounding by measles immunization, we adjusted for
socioeconomic variables and other factors that are known to be
important predictors of immunization. Hence, it is unlikely that
residual confounding by this variable would entirely explain the
observed strong protective association.
When we adjusted the relationship between tomato intake and morbidity
or mortality rates for total vitamin A intake, children in the higher
categories of tomato consumption were still at significantly reduced
risks for these adverse outcomes. This finding suggests that the
observed protective relationships may be explained by nutrients in
tomatoes other than vitamin A. Tomatoes are a rich source of
antioxidants, including lycopene,
- and ß-carotene and vitamin C.
Lycopene, a nonprovitamin A carotenoid, has an exceptionally high
capacity for scavenging free radicals (DiMascio et al. 1989
). It is responsible for the red color of tomatoes and is
available in tomatoes in concentrations that are 3040 times those of
ß-carotene (Beecher 1998
). The inverse relationships
between tomato consumption and the risks of cancer and cardiovascular
disease (Francheschi et al. 1994
, Giovannucci 1999
, Giovannucci et al. 1995
) have been
attributed to its high content of antioxidant substances including
carotenoids, mainly lycopene. Oxidative stress may also contribute to
the occurrence of diarrheal disease and malnutrition among children
(Khaled 1994
), and antioxidants, including lycopene, may
be beneficial in reducing the risk of these adverse conditions.
Lycopene may be associated with enhanced immunity and reduced risks of
infectious disease. In a study among healthy men, 2 wk of ingestion of
tomato juice resulted in a significant increase in lycopene levels, as
well an increase in T-lymphocyte function (Watzl et al. 1999
). Plasma lycopene levels were also significantly low in
malnourished children from Morocco (Houssaini et al. 1997
) and Nigeria (Becker et al. 1994
) and among
human immunodeficiency virusinfected children (Periquet et al. 1995
). In animal studies, intraperitoneal or intravenous
injection of lycopene prolonged the survival of bacterially infected
mice (Lingen et al. 1959
). In two inflammatory
conditions associated with oxidative stress, cystic fibrosis and septic
shock, patients were reported to have low levels of antioxidants
compared with controls (Goode et al. 1995
,
McGrath et al. 1999
). Other antioxidants in tomatoes,
including
- and ß-carotene and vitamin C, are associated with
protective effects on the immune system and have been associated with a
reduced risk of infection (Gaby and Singh 1991
,
Garland and Fawzi 1999
, Hemila 1997
).
Tomatoes are widely consumed in many parts of the world. In
sub-Saharan Africa, where child mortality, morbidity and
malnutrition rates are particularly high, tomatoes are consumed as raw
fruit but also as processed paste or sauce that is added to food during
cooking, which incidentally improves the bioavailability of lycopene
and other carotenoids (Tonucci et al. 1995
). To our
knowledge, this is the first study that examined the relationship of
tomato intake and infectious disease and mortality rates in childhood.
Additional data on this subject are needed. Nonetheless, our data
emphasize the importance of considering food-based approaches to
the prevention of micronutrient malnutrition and reduction in child
morbidity and mortality rates in developing countries.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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3 Abbreviation used: CI, confidence interval. ![]()
Manuscript received March 22, 2000. Initial review completed April 28, 2000. Revision accepted June 27, 2000.
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