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To assess the influence of infant breast feeding on C reactive protein (CRP), a marker of low grade inflammation associated with cardiovascular mortality independent of serum cholesterol concentrations.
Serum CRP, total cholesterol, anthropometric, and blood pressure measurements were performed along with assessment of infant breast feeding duration, birth weight, smoking status, adult socioeconomic status, number of health problems, and hormonal contraceptive use.
A New Zealand predominantly European descent community birth cohort.
822 men and women aged 26 years.
There was a significant linear relation (p<0.001) between duration of breast feeding and adult CRP level in women. The geometric means (IQR) for CRP were 2.22 (1, 4) mg/l for women breast fed for six months or more and 3.95 (2, 8) mg/l for women not breast fed (ratio, 95% confidence interval (CI): 0.69 (0.55 to 0.87). The linear association between cholesterol and breast feeding was also significant (p=0.01), the geometric mean (IQR) total cholesterol levels being 4.62 (4.10, 5.10) for those breast fed for six months or more and 5.04 (4.5, 5.80) for those not breast fed (ratio, 95% CI: 0.92 (0.87, 0.98). There was no relation between CRP or total cholesterol and duration of breast feeding in men.
The findings of lower CRP with an increased duration of breast feeding in women suggest early postnatal nutrition may influence long term cardiovascular risk.
C reactive protein (CRP), a marker of longstanding low grade inflammation, has recently been shown to predict cardiovascular mortality independent of serum low density lipoprotein cholesterol concentrations.1 A relation has been reported between infant breast feeding, adult cholesterol levels, and cardiovascular mortality.2,3,4 These findings suggest early childhood nutrition is an important determinant of adult cardiovascular risk.
Few studies investigate the influence of early childhood feeding on markers of low grade inflammation such as CRP. Recently, a randomised study of adolescents born before term has reported that those randomised to breast milk feeding had lower CRP concentration and low density to high density lipoprotein ratio.5 It is not known whether these findings apply to a broader population of children assessed in adulthood. We addressed this question in a well characterised community cohort of young adults.
Participants were members of the Dunedin multidisciplinary health and development study, a longitudinal investigation of health and behaviour in a birth cohort. The study members (n=1037) were born in Dunedin, New Zealand between April 1972 and March 1973, and represent the full range of socioeconomic status in the general population of New Zealand's South Island. They are primarily of European descent. Follow ups have been carried out at ages 3, 5, 7, 9, 11, 13, 15, 18, 21, and most recently at age 26 years when we assessed 980 (96%) of the 1019 study members still alive.
The study was approved by the Otago ethics committee and participants gave written informed consent. At the age 26 assessment venepuncture was performed between 4.15 to 4.45 pm. Ninety per cent (n=882) consented to venepuncture, with complete results available for 866 participants. Pregnant women, those who had low BMI (<18.5), and those who refused anthropometry (total n=44) were excluded from the analysis, leaving complete observations for 822 participants. Non‐fasting serum CRP (Boehringer Mannheim immunoturbidimetric assay, lower detection limit 1 mg/l), total cholesterol (homogenous enzymatic colorimetric assay), anthropometric, and blood pressure measurements were performed along with assessment of smoking status (those who had smoked daily for a month or more during the previous year were considered smokers), adult socioeconomic status (SES) using the Elley‐Irving scale,6 number of health problems during the previous five years (anaemia, arthritis, cancer, diabetes, epilepsy, heart trouble, kidney/bladder infections, and major surgery), and current hormonal contraceptive use.
Participants were categorised by the duration of breast feeding as; none (bottle fed), 0–3 months, 3–6 months, or 6 months or more using data collected by interviewing the mother at the 3 year old assessment (response rate 99.8%). These maternal reports were validated against prospective records made by Plunket nurses who completed regular home visits between birth and age 3 years.7 Because of the skewed nature of the distribution, data for CRP were log transformed after adding 1 to each value. Geometric means and the interquartile range are reported for CRP and cholesterol for each category of breast feeding. Multiple regression analysis, adjusting for birth weight, adult waist circumference, SES, smoking status, and oral contraceptive use, with an interaction term between sex and breast feeding was used to compare the relation between CRP and cholesterol with duration of breast feeding in men and women. Significance for all analyses was defined as p<0.05.
Table 11 details the characteristics of the study participants. Women had higher CRP levels than men but similar levels of serum cholesterol. There were no differences in adult waist girth, systolic and diastolic blood pressures for men or women breast fed for six months or more compared with the remainder of the sample.
There was no relation between infant breast feeding and CRP levels in men. In contrast there was a strong relation between duration of breast feeding for three or more months and lower CRP levels in women (table 22).). A multivariate analysis adjusting for, birth weight, adult waist girth, smoking, adult SES, number of health problems, and hormonal contraceptive use showed infant breast feeding was independently associated with adult CRP levels in women. Waist girth and oral contraceptive use were also associated with CRP.
Women breast fed for six months or more had lower total cholesterol levels compared with women not breast fed, ratio 0.92, (95% confidence interval (CI): 0.87 to 0.98). Total cholesterol levels in men breast fed for six months or more were similar to the remainder of the study sample, ratio 0.99 (95% CI: 0.93, 1.04). The sex interaction for trend was not significant (p=0.07).
The 822 participants did not differ from the remainder of the sample for sex, birth weight, being before term (less than 37 weeks gestation), small for gestational age, SES at birth, or for the breast feeding categories used in this study. Differences in waist, systolic, and diastolic blood pressure at age 26 years were not statistically significant between this sample and those not included.
These results underscore the importance of infant nutrition as an influence on cardiovascular risk factors in adult life. Our findings confirm a previous study showing a relation between adult total cholesterol level and duration of breast feeding in women.2 Furthermore, we have shown that duration of infant breast feeding in women seems to favourably influence adult levels of CRP, a marker of low grade longstanding inflammation and predictor of long term cardiovascular risk.1 These findings extend those of previous reports where CRP concentration in adolescence was influenced by breast milk feeding in before term infants.5
It is unclear why the duration of breast milk feeding seemed to influence CRP levels in women and not men. The results do not seem to be influenced by differences in abdominal obesity as our analysis controlled for waist measurement. Similarly we controlled for serum cholesterol and other known influences of CRP levels. A potential explanation for the findings may relate to either the different hormonal milieu in adult men or women or alternatively different sensitivities to constituents of breast milk during early infancy. A limitation of the study was the use of a low sensitivity CRP assay and the absence of adjustment for a family history of cardiovascular disease or physical activity.
Our findings suggest infant breast feeding should be encouraged to improve long term cardiovascular risk.
There is evidence that early postnatal nutrition can influence long term cardiovascular risk factors and the propensity for developing cardiovascular disease.1,2,3,4,5 It has been hypothesised that accelerated early growth may explain the adverse long term cardiovascular effects of a nutrient enriched diet in infancy.8 Breast fed infants have slower early growth and subsequently have a lower risk of multiple cardiovascular risk factors than formula fed infants.8 Our findings of lower CRP with an increased duration of breast feeding in women are consistent with the growth acceleration hypothesis.
Funding: data collection was supported by grants from the National Heart Foundation of New Zealand, the University of Otago (Otago Research Grant), NIMH Grants MH45070 and MH49414, and the WT Grant Foundation. The funding sources had no involvement in the performance of the study or the writing of the manuscript.
Competing interests: none declared