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C P M Leeson a Medical
Research Council Childhood Nutrition Research Centre, Institute of
Child Health, London WC1N 1EH, b Vascular Physiology Unit, Great Ormond Street Hospital for
Children, London WC1N 3JH
Correspondence to: C P M Leeson cpm_leeson{at}hotmail.com
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Abstract |
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Objectives:
To test the hypothesis that duration of
breast feeding is related to changes in vascular function relevant to the development of cardiovascular disease.
Nutrition in early postnatal life may have major, long term
"programming" effects on the physiology, metabolism, and clinical outcome of animals and humans.1-3 Coronary artery disease
is one outcome in humans linked to early growth and nutrition. Although breast feeding has been associated with a lower risk of cardiovascular disease, men born earlier this century who had still been breast fed
aged 1 year had higher rates of ischaemic heart disease 60-70 years
later compared with the expected rate for men of that
age.2 If this observation were causal, it would raise an
important question about the optimal duration of breast feeding.
Although observational evidence linking early nutrition to later
cardiovascular disease might be subject to confounding, experimental evidence also exists linking atherosclerosis and breast feeding in
non-human primates. Studies in baboons that were breast fed or formula
fed throughout infancy and then placed on a Western style diet, high in
saturated fats, showed that those previously breast fed had an abnormal
lipid profile and more arterial fatty streaks in
adulthood.1 One hypothesis was that breast feeding programmed baboons to be conservative with cholesterol We studied a UK population to test further the hypothesis that duration
of breast feeding might influence later emergence of vascular disease.
To minimise potential influences of other lifestyle factors throughout
adulthood we studied a young cohort. This was feasible because early
pathophysiological changes in the artery, relevant to the development
of atherosclerosis, can now be measured early in life with non-invasive
imaging techniques.
4 5
Our group has already shown links
between vascular dysfunction and growth and nutrition during
childhood.
6 7
In this study, we measured arterial
distensibility, a measure of vessel wall stiffness, in a large cohort
of adults in their 20s and related it to duration of breast feeding.
Study design
Measurement of cardiovascular risk factors
Vascular study measurements
Statistical analysis
We sent invitations to 1526 people, of whom 420 (28%) agreed to
participate, 229 (15%) declined, and 877 (57%) did not reply. In all,
344 (23%) subjects were able to attend for vascular investigations. Full details of vascular function, risk factors, and infant feeding practice were available for 331 (96%) of these (table 1). The study group had similar body size, body mass index, blood pressure, and
smoking rates to young adults generally in the United
Kingdom.11
Table 1.
Design:
Population based observational study.
Setting:
Cambridge.
Participants:
331 adults (171 women, 160 men) aged
between 20 and 28 years, born in Cambridge Maternity Hospital.
Main outcome measures:
Distensibility of brachial
artery, type and duration of infant feeding, current lipid profile, and
other cardiovascular risk factors.
Results:
The longer the period of breast feeding the less distensible the artery wall in early adult life, with no sex
differences (regression coefficient =
3.93 µm/month, 95% confidence interval
7.29 to
0.57, P=0.02). However, in those breast fed for less than four months, arterial distensibility was not
significantly reduced compared with an exclusively formula fed group.
The vascular changes observed were not explained by alterations in
plasma cholesterol concentration in adult life.
Conclusions:
Breast feeding in infancy is related to
reduced arterial function 20 years later. These data should not alter current recommendations in favour of breast feeding, which has several
benefits for infant health. Further work is needed, however, to explore
the optimal duration of breast feeding in relation to cardiovascular outcomes.
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Introduction
Top
Abstract
Introduction
Participants and methods
Results
Discussion
References
perhaps appropriately for their natural diet
but when they consumed a Western
diet this programming led to arterial disease. Were these findings
supported in humans, it would have implications for infants weaned on
to a Western diet.
![]()
Participants and methods
Top
Abstract
Introduction
Participants and methods
Results
Discussion
References
We studied 331 subjects (160 men; 171 women) aged 20 to 28 years
born in Cambridge Maternity Hospital. We invited random samples of
those born between 1969 and 1975 to attend a clinic for evaluation of
cardiovascular risk profile by venepuncture, questionnaire, physical
measurements, and vascular studies. Invitations were sent until the
planned sample size was reached. Ethical approval and informed consent
were obtained. To determine possible biases in the study sample, we
compared the distribution of risk factors in this group to that in the
United Kingdom and to data obtained in our questionnaire from a
subgroup of people who initially declined to participate.
We analysed a fasting venous blood sample for insulin, glucose,
and lipid profile using routine methods. Weight, height, blood
pressure, and smoking history were recorded. We assessed social
influences by attained education level and socioeconomic
groupings.8 Before attending, participants collected information from their mothers on how they had been fed as an infant.
We grouped them as either only bottle fed or having received breast
milk. For those who had been breast fed, we recorded how long breast
feeding had continued.9
Distension of the brachial artery during the cardiac cycle was
measured as described previously.
7 10
Briefly, the artery
was imaged with an Acuson 128XP/10 and movement of the arterial walls
recorded with an automated wall tracking system (Ingenious Medical
Systems, Arnhem, Netherlands). By relating change in diameter over the
cardiac cycle to pulse pressure, "stiffness" of the vessel wall can
be quantified.
We assessed continuous relations between explanatory variables and
arterial distensibility using multiple regression. Variables were
related to absolute distension with pulse pressure, age, sex, and
vessel size as independent variables.7 Further models
examined adjustment for other factors. To investigate the effect of
duration of breast feeding further, the group was dichotomised around
the median duration of breast feeding. We then assessed differences
between these divisions, as well as other groups (such as breast fed
compared with bottle fed), using t tests. Distensibility was represented as a coefficient (change in arterial cross sectional area between diastole and systole relative to the area at diastole, divided by pulse pressure).
5 7
![]()
Results
Top
Abstract
Introduction
Participants and methods
Results
Discussion
References
Arterial distensibility
The distensibility coefficient was 0.129 mm Hg-1 in men and 0.145 mm
Hg-1 in women (95% confidence interval for
difference
0.032 to
0.002, P=0.04). There was no variation with
age (regression coefficient=
1.6, 95% confidence interval
4.9 to
1.8, P=0.36). As expected, reduced distensibility was related to
increased total serum cholesterol concentration and systolic blood
pressure (table 2).7 Social class and smoking were
unrelated to arterial function. Arterial distensibility was not related
to birthweight or weight in infancy.
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3.93 µm/month, 95% confidence interval
7.29 to
0.57, P=0.02)
(figure). The regression coefficient was negative in men (
2.9) and
women (
4.3) analysed separately, although because of reduced sample size the result was significant only in women. There was no interaction between sex and duration of breast feeding, and we therefore conducted further analyses on the combined cohort. Participants who had been
exclusively breast fed for less than four months had similar distensibility to those who had never been breast fed (distensibility in bottle fed=0.1388 mm Hg-1 and breast fed less
than four months=0.1457 mm Hg-1, mean
difference=0.007 mm Hg-1, 95% confidence
interval
0.026 to 0.012, P=0.46). Those who had been breast fed for
four months or more had significantly lower distensibility than those
who had been breast fed for less than four months (distensibility for
those breast fed for four months or more=0.1200 mm
Hg-1, mean difference from those breast fed for
less than four months=
0.026 mm Hg-1,
0.038
to
0.048, P=0.02).
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Relation of duration of breast feeding to cardiovascular risk
factors and other variables
Duration of breast feeding was unrelated to lipid profile,
body size, body mass index, smoking patterns, blood pressure, social
class, birthweight, or prevalence of premature cardiovascular disease
in relatives (regression coefficient between duration of breast feeding
and cholesterol concentration=
0.16 months/mmol/l, 95% confidence
interval
0.49 to 0.17, P=0.4). The strength of the association
between duration of breast feeding and distensibility was unaffected by
inclusion of current lipid profile, body mass index, height, weight, or
social class in the regression model (table 3).
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Discussion |
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We found that distensibility of the brachial artery in young adults was related to the duration of breast feeding in infancy. Longer duration of breast feeding was associated with stiffer arteries. As we studied young adults, our results are less likely to be confounded by the effects of other cardiovascular risk factors that are present in older cohorts. The results suggest that the effect of breast feeding on cardiovascular risk occurs early in life.
Possible explanations for the effect
Breast feeding evolved in mammals over millions of years and is
generally considered optimal for humans. The commonly cited advantages
over formula feeding include reduced infection and atopy and increased
cognitive development.12 The optimal duration of breast
feeding remains inadequately researched. We found an apparent adverse
outcome in people who had had prolonged breast feeding. This finding is
consistent with the results of an observational study in which men who
had been breast fed at 1 year had an increased risk of ischaemic heart
disease 60 years later.2 This finding was suggested to be
due to programming of cholesterol metabolism in response to the unique
lipid or hormone contents of breast milk. These factors might alter
expression of hepatic enzymes or low density lipoprotein receptors,
changing the response to a high fat diet later in
life.13-16 This hypothesis is consistent with the
experimental studies in primates, where breastfed baboons given a
Western style high saturated fat diet had more early atherosclerotic
changes in adulthood than formula fed animals.
Relevance of arterial distensibility
Arterial distensibility is known to diminish with age in relation
to cardiovascular risk factors and is reduced in subjects with frank
coronary disease.
22 23
Indeed, the potential impact of
such risk factors is apparent in this study, which showed reduced
arterial distensibility in young adults with higher blood pressure,
cholesterol, or body mass index. Although further investigation is
needed, it seems likely that arterial distensibility is related to risk
of vascular disease.
Implications
We emphasise that our observational data do not establish a causal
relation between length of breast feeding and cardiovascular disease.
Nevertheless, our findings are supported by previous human and
experimental animal data.
1 2
We tried to minimise
confounding by studying a young cohort and adjusted for potential
influences on distensibility that might also relate to duration of
breast feeding. Further confounding should be explored in future studies.
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What is already known on this topic
No data exist on the optimal duration of breast feeding One study found that men who had been breast fed at 1 year had higher rates of ischaemic heart disease What this study addsArterial distensibility (a marker of early cardiovascular disease) in adults aged 20-28 decreased with increasing duration of breast feeding No difference in distensibility was found between participants who had been bottle fed and those breast fed for less than four months Duration of breast feeding was not related to cholesterol concentration in adulthood Any effect of breast feeding on cardiovascular risk probably occurs in infancy |
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Acknowledgments |
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We thank Ian Merryweather, Sarah Jones, and Tristan Cope for help with data collection and laboratory analysis and Dr David Muller for coordinating the biochemical work.
Contributors: CPML and AL designed the study, analysed and interpreted the data, and wrote the paper. MK and JED contributed to the design of the study and revision of the paper. CPML and MK managed the study and data collection. CPML and AL will act as guarantors.
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Footnotes |
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Funding: The work was funded by the Medical Research Council. All work in the Institute of Child Health and Great Ormond Street Hospital also benefits from NHS research and development funding.
Competing interests: The centre has collaborated with the infant food industry for its outcome studies on nutrition.
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References |
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(Accepted 15 December 2000)
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