Introduction
The World Health Organization (WHO) recommends exclusive breastfeeding from birth to 6 months, the introduction of nutritious complementary foods at 6 months and continued breastfeeding for 52 years. 1 Breastfeeding reduces morbidity and mortality from infection during infancy, and the timely introduction of nutritious complementary foods prevents stunting. 2, 3 Optimal infant feeding may also have longterm benefits. Adults and children who were breastfed have lower blood pressure (BP) and lower rates of obesity and type 2 diabetes than those who were bottle-fed, [4] [5] [6] [7] [8] with benefit proportionate to the duration of breastfeeding. [9] [10] [11] [12] [13] [14] This has been attributed to better appetite regulation and/or lower weight gain in breastfed infants, and/or effects of nutrients or bioactive constituents in breast milk. 6 Fewer studies have investigated long-term associations with the timing of initiation of complementary feeding, but lower rates of childhood obesity have been reported among those who started complementary foods later. [15] [16] [17] A limitation of the published evidence linking breastfeeding to later health is reliance on maternal recall of infant-feeding practices, sometimes many years later. [6] [7] [8] [9] [10] [11] [12] [13] [14] Few studies had data on duration of breastfeeding, and almost none had information on complementary feeding. The majority were conducted in high-income countries, where mothers who follow prescribed infant-feeding guidelines tend to be from higher socio-economic and more educated groups. 18, 19 Associations of infant feeding with later adiposity and other risk factors are usually attenuated after adjusting for these confounding factors, suggesting that generally healthier family lifestyles, rather than infant feeding, explain the lower disease risk.
Introduction
In low-and middle-income countries (LMICs), breastfeeding tends to be the norm, but many mothers introduce complementary foods and stop breastfeeding too early. 2 Obesity, diabetes and cardiovascular disease are rising rapidly in these countries. 20 Promoting optimal infant-feeding practices could be a low-cost intervention to improve lifelong health. Data from LMICs may help address confounding issues, because relationships between infant-feeding practices and social class differ from those in high-income settings. The current study analyses data from the COHORTS collaboration (Consortium on Health Orientated Research in Transitional Societies) 21 comprising birth-cohort studies in five LMICs. Our objective was to test the hypothesis that initial breastfeeding, longer duration of breastfeeding and later introduction of complementary foods are associated with lower adult BP, glucose concentrations and adiposity.
Methods

Description of the cohorts
The collaboration among the five cohorts (Table 1) was originally established to contribute a paper for a Lancet Series on Maternal and Child Nutrition. 22 One author (C.G.V.) approached the principal investigators of all follow-up studies in LMICs with 1000 or more subjects aged 515 years; all agreed to participate. The cohorts include the 1982 Pelotas (Brazil) Birth Cohort; 23 the Institute of Nutrition of Central America and Panama Nutrition Trial Cohort (INTCS, Guatemala); 24 the New Delhi (India) Birth Cohort Study; 25 the Cebu (Philippines) Longitudinal Health and Nutrition Survey (CLHNS) 26 and the Birth to Twenty (BTT-South Africa) cohort. 27 The Guatemala cohort was based on a randomized controlled trial of protein-energy supplementation for the pregnant mothers of the cohort members, and for the cohort themselves as young children; 24 the others were observational studies. All studies were approved by institutional research ethics committees, and participants gave informed consent.
Feeding data
The methods used to collect infant-feeding data varied among the cohorts (Table 1) . We defined complementary foods as semi-solid or solid foods. Variables used in the analysis were (i) whether an individual was ever breastfed (yes/no), available for all five cohorts; (ii) total duration of breastfeeding (nine categories from 0 to 424 months), available for all cohorts except India and (iii) age at which complementary foods were introduced (six categories In Brazil and the Philippines, the number included in this analysis exceeds the number of participants in the last follow-up study, because some data (e.g. height) was utilised from previous follow-up rounds.
Feeding data
from <3 to 418 months), available for all cohorts except Guatemala.
Adult outcomes
Except for the South African participants who were adolescents (mean age 15 years), all others were young adults. For simplicity, these measures are referred to as 'adult' outcomes. Systolic BP (SBP) and diastolic BP (DBP) were measured by aneroid sphygmomanometer in Brazil, mercury sphygmomanometer in the Philippines and digital devices elsewhere (Guatemala: UA-767, A&D Medical; India: Omron 711; South Africa: Omron M6), using appropriate cuff sizes, after 5-10 min of being seated. The average of two or three measurements was used. 21 Hypertension was defined as SBP 5140 mmHg or DBP 590 mmHg and pre-hypertension as SBP 5130 mmHg or DBP 580 mmHg. In South Africa, we defined pre-hypertension as SBP or DBP 590th percentile of age-, sex-and height-specific cut-off points.
Adult outcomes
28 Across all cohorts, <0.5% of participants were on anti-hypertensive medication.
Adult outcomes
Fasting glucose concentrations were measured in venous plasma (India and South Africa) or capillary plasma (Guatemala) using standard laboratory enzymatic methods, and in venous whole blood (Philippines) using a glucometer ('One Touch', Johnson & Johnson Ltd). In Brazil, random fingerprick capillary whole blood glucose was measured by glucometer (Accu-Check Advantage, Roche Ltd); values were adjusted for time since the last meal. 29 Glucometers overestimate glucose concentrations in whole venous blood compared with standard laboratory methods; 30, 31 we subtracted 0.97 mmol/l from the Philippine values. 30 Diabetes was defined as a glucose concentration 57.0 mmol/l, and impaired fasting glucose (IFG) as a concentration 56.1 and <7.0 mmol/l. . 33 Percentage body fat was estimated in Brazil using bioimpedance and a Deuterium-validated equation; 34 in Guatemala, using weight, height and waist circumference with an equation developed using hydrostatic weighing; 35 in India and the Philippines, using skinfold equations validated for Asian populations; 36, 37 and in South Africa, using dual-energy X-ray absorptiometry (Hologic Delphi).
Confounding variables
Earlier research in these cohorts [38] [39] [40] [41] [42] indicated that the following should be considered as possible confounding factors: maternal socio-economic status (SES), education, age, smoking, rural/urban residence and race and infant birth weight. For SES at birth, a five-level variable was created for each cohort (1 ¼ least and 5 ¼ most advantaged), using a principal components analysis of household income and/or assets and services (Brazil, Guatemala, Philippines and South Africa) or the father's occupation (India). Information on maternal smoking was not available for Guatemala and India, where maternal smoking was almost non-existent at that time; we assumed all were non-smokers. Brazil and South Africa had racial/skin colour subgroups; we created variables for white, black, mixed-race and Asian groups. The Brazil, India and South Africa cohorts were urban, and the Guatemala cohort rural; in the mixed rural and urban Philippine cohort, an 'urbanicity index' was used. 43 Missing data and final analysis sample There was minimal missing data in Brazil, the Philippines and South Africa ( Table 2 ). In the Guatemala cohort, age of introduction of complementary foods was not recorded, and duration of breastfeeding was missing for 48% of the participants. Missing data arose from the study design; recruitment included pregnant women and children 47 years at baseline; infant feeding was not recorded for children 415 months of robertkeller@example.net. Participants with missing data were older, more adipose and more likely to have diabetes or hypertension. In India, duration of breastfeeding was not recorded, and age of introduction of complementary foods was missing for 61% of the participants. Those with missing data were younger and less adipose.
Confounding variables
The analysis sample (n ¼ 10 912) included participants with data on at least one of the three infant-feeding variables and at least one adult outcome (BP, glucose concentration or body composition), and excluded women who were pregnant at the time of the outcome measurements.
Statistical methods
Variables with skewed distributions were log transformed (glucose concentrations, skinfolds). Associations among feeding variables, potential confounders and adult outcomes were assessed within each cohort and in pooled data, using linear or logistic regression or chi-square tests. Categorized duration of breastfeeding and age at introduction of complementary foods were treated as continuous variables in linear regression models, and non-linear associations were tested using quadratic terms. Models were initially adjusted for age and sex only, and then for the set of confounding variables, adult BMI (not done for the adiposity outcomes) and height. Parameter estimates given in the text are fully adjusted. All pooled models were adjusted for cohort location and included interaction terms between cohort location and each confounding variable. We tested for heterogeneity of associations across the five sites by using (for continuous variables) F-tests from nested linear regression models and (for binary outcomes) chi-square tests based on the difference in deviance between nested models; where there was significant heterogeneity (P < 0.05), we present data separately for each site. Sex differences were tested using interaction terms.
Results
The number of participants included in this analysis, as a percentage of the original live births in each cohort, ranged from 19% in India to 75% in Brazil (Table 1) . More than 90% of babies in all cohorts were initially breastfed ( Table 2 ). The most frequent duration of breastfeeding was 1-3 months in Brazil, 12-18 months in Guatemala and the Philippines and 42 years in South Africa, and the most frequent age at introduction of complementary foods was 0-3 months in Brazil and South Africa, 3-6 months in the Philippines and 9-12 months in India.
Predictors of infant-feeding variables
Associations between the confounding variables and infant-feeding variables are presented in Supplementary Tables A-G; Supplementary data are available at IJE online. To summarize these data: in Brazil, women of lower SES/education were less likely to initiate breastfeeding, and tended to breastfeed for either a short or long duration (Supplementary Tables A and  B ; Supplementary data are available at IJE online). In the Philippines and South Africa, women of lower SES/education were more likely to initiate breastfeeding and breastfed for longer. In Brazil, India and the Philippines, more affluent/educated mothers introduced complementary foods earlier. In Brazil and Guatemala, women who breastfed for longer tended to be older (Supplementary Table C Mean age at adult follow-up ranged from 16 years (South Africa) to 32 years (Guatemala) ( Table 3 ). The prevalence of hypertension ranged from 1% (Philippines, females) to 17% (Brazil, males), of diabetes from <1% (Philippines and South Africa) to 4% (Brazil and India, males) and of obesity from 1% (Philippines, females) to 25% (Guatemala, females).
Ever vs never breastfed
In the pooled data, there were no differences in BP, glucose or body-composition outcomes between participants who were initially breastfed compared with those not breastfed (Tables 4 and 5 ). There was heterogeneity between sites for DBP (Table 4) ; in Brazil, DBP was lower among participants who were breastfed [À1.5 mmHg, 95% confidence interval (CI) À2.7 to À0.3], whereas in the Philippines and South Africa there was a trend in the opposite direction (Philippines: 1.3 mmHg, 95% CI À0.5 to 3.1; South Africa: 1.4 mmHg, 95% CI 0.6-2.2). There was also heterogeneity between sites for prevalence of overweight (Table 5) 
Breastfeeding duration
In the pooled data, there were U-shaped associations between breastfeeding duration and all the BP outcomes (Table 4, Figure 1 ). For SBP and hypertension, these remained after adjustment for confounding factors, adult BMI and height. The lowest mean BPs were observed among participants who had been breastfed for 3-6 months; there was a difference of $2 mmHg between the lowest and highest mean values (Figure 1) . Several of these U-shaped associations showed borderline heterogeneity across the cohorts (Table 4) . A U-shaped association was clear only in Brazil ( Figure 1) ; there was an upward trend in Guatemala, and no apparent trends with duration of breastfeeding in the Philippines and South Africa. After excluding the Brazil data, there were no linear or U-shaped associations between breastfeeding duration and any BP outcome.
Breastfeeding duration
There was no heterogeneity among the cohorts for glucose or body-composition outcomes. There was a U-shaped association between breastfeeding duration and IFG þ diabetes mellitus (DM) ( Table 4) , and an inverse association between breastfeeding duration and adult skinfold thickness (Table 5) . However, these associations were attenuated after adjusting for confounding variables.
Breastfeeding duration
There were no changes in the findings if the Guatemala cohort, in which duration of breastfeeding was missing for 48% of participants, was excluded from the analysis. In the Guatemala data, there was an interaction between intervention group and duration of breastfeeding for only one outcome (adult BMI); there were no changes in the findings when the two intervention groups were considered as separate populations.
Introduction of complementary foods
The age at introduction of complementary foods was unrelated to the BP and glucose outcomes (Table 4) . There was no significant heterogeneity among the cohorts.
Introduction of complementary foods
Later introduction of complementary foods was associated with lower adult BMI, waist circumference and percentage body fat, thinner skinfolds, and a lower risk of overweight/obesity (Table 5, Figure 2) . The findings were similar after excluding the India cohort, which had a higher mean age at introduction of complementary foods, and in which data were missing for 61% of participants. Inverse associations were still present for BMI, waist circumference and subscapular skinfolds, which fell by 0.19 kg/m 2 (95% CI 0.01-0.37), 0.45 cm (95% CI 0.02-0.88) and 3.1% (95% CI 0.6-5.4; the percentage change in skinfolds is cited here rather than the change in millimetres, because the skinfold values were logged for analysis), respectively, per category increase in age of introduction of complementary foods. When the analysis was limited to the period up to 6 post-natal months, these associations were attenuated; BMI, waist circumference and subscapular skinfold thickness fell by 0.21 (95% CI À0.03 to 0.45), 0.45 cm (95% CI À0.11 to 1.01) and 2.6% (95% CI À0.9 to 6.1), respectively, per 3-month category.
Introduction of complementary foods
Earlier introduction of complementary foods was associated with higher infant weight at 2 years (Supplementary Table H ; Supplementary data are available at IJE online). After adjusting for 2-year weight, the inverse associations between age of introduction of complementary feeds and adult adiposity were no longer present.
Introduction of complementary foods
There was no consistent evidence of differences according to sex, or the age at which outcomes were measured, in any of the associations described. 123 (14) 111 (13) 117 (11) 108 (131) 118 (11) 107 (11) 112 (11) 99 (10) 118 (13) 111 (12) DBP (mmHg) 76 (12) 72 (11) 72 (9) 70 (9) 78 (10) 73 (9) 76 (10) 68 (9) 68 (10) 69 (9) Hypertension (%) 
Discussion
We combined data from five birth cohorts in LMICs, to examine associations between infant feeding and risk factors for cardiovascular disease (BP, glucose concentrations and adiposity) in 410 000 young Data were analysed using linear regression (continuous outcomes, B is the regression coefficient) or logistic regression (dichotomous outcomes, OR). Model 1 adjusted for subject's age and sex only; Model 2 further adjusted for confounders (maternal SES, education, age, smoking, race, rural/urban residence and birth weight) and adult BMI and height; p-het is the test for heterogeneity of the coefficient across studies in Model 2.
Discussion
a Categories are as indicated in Table 2 . There were no non-linear associations with age at introduction of complementary foods, and these data have been omitted.
INFANT-FEEDING PATTERNS AND CARDIOVASCULAR RISK FACTORS
adults. There were no differences in risk factors between participants who were initially breastfed compared to those who were never breastfed. There were U-shaped associations between duration of breastfeeding and adult BP, with the lowest mean SBP among those breastfed for 3-6 months; however, these were small and inconsistent effects. After adjusting for confounding factors, there were no associations between duration of breastfeeding and adult glucose concentrations, DM þ IFG or body composition. Participants who started complementary foods later in infancy were less adipose and overweight in adult life. These associations were robust to adjustment for the set of confounding variables, but attenuated by adjustment for 2-year weight. Strengths of the study were that infant-feeding data were collected prospectively, reducing the risk of misclassification due to inaccurate maternal recall, and included duration of breastfeeding and introduction of complementary foods. Limitations were missing infant-feeding data and losses to follow-up in the older Guatemala and India cohorts. Missing data Data were analysed using linear regression (continuous outcomes, B is the regression coefficient) or logistic regression (dichotomous outcomes, OR). Model 1 adjusted for subject's age and sex only; Model 2 further adjusted for confounders (maternal SES, education, age, smoking, race, and rural/urban residence, and birth weight) and adult height; p-het is the test for heterogeneity of the coefficient of Model 2 across studies.
INFANT-FEEDING PATTERNS AND CARDIOVASCULAR RISK FACTORS
a Categories are as indicated in Table 2 . There were no non-linear associations with age at introduction of complementary foods, and these data have been omitted.
INFANT-FEEDING PATTERNS AND CARDIOVASCULAR RISK FACTORS
would influence population means and prevalence values for both exposures and outcomes, but the within-cohort associations of interest, between infant feeding and adult outcomes, would be less vulnerable to bias. Associations of duration of breastfeeding and age of introduction of complementary foods were little changed if the Guatemala and India cohorts were excluded from the relevant analyses. A further limitation of the study was heterogeneity among the cohorts in the methods for recording infant-feeding data. This reduced the number of exposures we could include (e.g. exclusive breastfeeding and predominant breastfeeding were definable in only one and three of the cohorts, respectively, and were not included), and we defined introduction of complementary foods as the introduction of solids rather than nutritious liquids and solids, the more generally used definition. The different methods would tend to reduce the precision of the exposure variables and thus attenuate any estimates of association with adult outcomes. The methods used for measuring adult outcomes also varied among the cohorts, although are all accepted techniques for epidemiological studies. BP was measured using a variety of devices, all of which perform to international standards, although systematic under-or overestimation of BP is recognized. [44] [45] [46] [47] Blood glucose was measured using standard laboratory assays or by glucometers, and although the latter are not recommended for clinical diagnosis of individual patients, their use in epidemiological studies is accepted. 48 Four studies measured fasting glucose; the Pelotas study used random glucose, adjusted for time since the last meal. 29 Adiposity was measured using similar anthropometric protocols in all studies, and percentage body fat was measured using a variety of techniques that have been validated in appropriate populations. Different techniques would influence the precision of measurements, which could obscure associations but is unlikely to create spurious associations. Systematic over-/underestimation of (say) BP or the prevalence of hypertension would not affect the ranking of the participants, and would not, therefore, substantially change the associations of interest. A consistent finding was that later introduction of complementary foods was associated with lower adult adiposity. Previous literature on this topic is mixed; some studies have reported findings similar to ours. [15] [16] [17] Others have reported no association 4, 49, 50 or an opposite association. 51 In our pooled data, there was a linear decrease in adult adiposity across the range of ages at which complementary foods were started (<3 months to 418 months; Figure 2) . Introduction of complementary foods 46 months is associated with nutritional inadequacy and growth faltering 1, 2 and cannot be recommended. However, in our data, there was a downward trend in adiposity with later introduction of complementary foods even in the first 6 post-natal months (Figure 2 ), although this was very small and likely to be of limited health significance. Earlier introduction of complementary foods is associated with greater infant weight gain, 52 and our results, showing no association after adjusting for 2-year weight, suggest that this could be a mediating factor.
INFANT-FEEDING PATTERNS AND CARDIOVASCULAR RISK FACTORS
There were no differences in outcomes between 'ever' vs 'never' breastfed groups. This contrasts with results from meta-analyses of observational studies, mainly in high-income settings, which have shown lower SBP (approximately À1 mmHg) and DBP (less than À0.5 mmHg), a 30-40% lower risk of type 2 diabetes and a 20% lower risk of overweight or obesity in children or adults who were breastfed. [6] [7] [8] [9] Possible explanations for our negative findings are that initiation of breastfeeding was almost universal in these cohorts (hence reducing power), and/or that the associations in the above studies result from residual confounding, not seen in our cohorts because of the different relationships between infant feeding and maternal SES.
INFANT-FEEDING PATTERNS AND CARDIOVASCULAR RISK FACTORS
There were U-shaped associations between duration of breastfeeding and BP outcomes. These trends were inconsistent among the five cohorts (Figure 1) . Overall, there was no evidence that longer duration of breastfeeding protects against the later development of hypertension or diabetes. Again, these findings differ from those reported from high-income settings, where most studies, 9, 10, 12, 53, 54 although not all, 55, 56 found lower BP and/or a lower risk of type 2 diabetes in children or adults who were breastfed for longer. Explanations could be, again, residual confounding in high-income populations; imprecision in the exposure measure due to different data-collection methods; or differences in other post-natal factors related to the adult outcomes, e.g. childhood growth, between low-and high-income populations.
INFANT-FEEDING PATTERNS AND CARDIOVASCULAR RISK FACTORS
A recent systematic review of studies in children and adults found a linear inverse association between duration of breastfeeding and risk of overweight/obesity in about half the studies. 14 The associations were diminished after adjusting for confounders, but remained in some studies. We found that participants who were breastfed for longer in infancy had thinner skinfolds, but the associations were attenuated by adjusting for confounding variables. Confounding has been a major limitation of studies linking infant feeding to later health. The ultimate solution to this problem would be randomized controlled trials, but it is not possible to randomize healthy babies into breastfed and non-breastfed groups. Helpful data will come from a large randomized trial of breastfeeding promotion, in Belarus, which greatly increased initiation rates and duration of breastfeeding. 57 In this trial, there were no differences in BP or adiposity between children from the intervention and control groups at 9 years. In another trial, among pre-term newborns, there was no difference in BP in childhood between those randomized to receive breast milk or formula, 58 but BP was lower in the breast-milk group in adolescence. 59 We know of no randomized trials of early vs late introduction of complementary foods.
INFANT-FEEDING PATTERNS AND CARDIOVASCULAR RISK FACTORS
In conclusion, in five high-quality birth cohorts in LMICs, we found no evidence that initial breastfeeding, or longer duration of breastfeeding, were protective against adult hypertension, diabetes or overweight/obesity. There are many proven benefits of breastfeeding, but the evidence that it reduces the risk of adult chronic disease is not compelling, at least in LMICs. We were not, however, able to examine 'exclusive breastfeeding' as an exposure, since this was available for only one of the cohorts. There was a consistent linear inverse association between age of introduction of complementary foods and adult adiposity. Our data suggest there may be modest protection against adult adiposity from delaying the introduction of complementary foods to the recommended 6 months. This association should be examined in other studies.
Supplementary Data
Supplementary data are available at IJE online.
Funding
on Alternative Development and the Anglo American Chairman's Fund. All authors/researchers are independent of the funding bodies.

{'paper_id': '14381853', 'title': 'Infant-feeding patterns and cardiovascular risk factors in young adulthood: data from five cohorts in low- and middle-income countries', 's2_url': 'https://api.semanticscholar.org/CorpusID:14381853', 'source': 'S2ORC'}