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Social and biological determinants of lactation

Salvador Villalpando, Samuel Flores-Huerta, Mardia López-Alarcón, and Ignacia Cisneros-Silva


During the last decades breastfeeding rates have fallen to such a level that at least one

million infant deaths annually have been attributed to the replacement of breastfeeding by formula-feeding. After the recent World Summit for Children, unprecedented efforts were targeted to reverse this trend. The evolution of breastfeeding patterns and related practices in Mexico is presented as a case study. Before the Baby-Friendly Hospital initiative, the rate of breastfeeding initiation and the average breastfeeding duration in Mexico were among the lowest in developing countries. The use of formula in hospitals was common. Knowledge about breastfeeding and awareness of its advantages were low among the public and health professionals. The International Code related to breastmilk substitutes became law, and the Baby-Friendly Hospital Initiative was included in the National Plan for Health in 1991. Formula manufacturers decided voluntarily to stop advertising their products. After five years, several surveys show noticeable changes in hospital policies and practices regarding breastfeeding promotion and improvement in the rate of breastfeeding initiation and exclusivity. Total duration of breastfeeding, public awareness, and mothers' knowledge about the basics of breastfeeding are increasing. Despite continued inadequate post-partum support and counselling, and an inconsistent effectiveness in conveying to the public the benefits of breastfeeding, progress has been made in the last five years and will be reflected in improved infant health in the near future.


Humans are the only mammals whose offspring survives without natural lactation. This has been made possible on a worldwide scale by technological developments for modifying and preserving milk from other species [1]. As a result, the breastfeeding rate in developed countries has fallen dramatically. In the mid-1940s, about 50% of infants were breastfed up to three months in England and Australia; by 1971, only 25% of American babies were breastfed. Concerns regarding the negative effects of artificial feeding of infants resulted in the active promotion of breastfeeding as a healthier feeding mode. Currently, up to 80% or more of mothers breastfeed up to six months in some countries, although rates are highly variable [2].

A similar decline in the rate of breastfeeding has occurred in developing countries. It started 20 to 30 years later than in their affluent counterparts. The deadly consequences of such a decline are eloquently summarized by Stephen [3] in his report as a representative of the United States Government to the 34th World Health Assembly. He pointed out that at least one million infant deaths in developing countries are due to diarrhoea and malnutrition associated with formula-feeding. As part of the multinational agreement signed during the World Summit for Children, important national and international efforts were directed towards curbing and reversing the prevalence of formula-feeding in developing countries.

Mexico: A case study

To address the social and biological determinants of lactation establishment, I will present the case study of Mexico as an example, because Mexico lags behind many Latin American countries in improving the frequency and duration of breastfeeding [4]. The social determinants will be classified as (1) the general framework represented by the economy and the pertinent national policies, (2) the organizations acting as health-care purveyors, (3) the training and commitment of health-care professionals, and (4) the individuals participating in the process of lactation.

The magnitude of the problem in Mexico

Before the Baby-Friendly Hospital Initiative started its operation in Mexico in 1991, the frequency of breastfeeding was highly variable in rural, urban, and metropolitan communities. Recently, Pérez-Escamilla reviewed the studies reporting the prevalence of breastfeeding in Mexico from 1953 to 1988 [5]. In these studies the percentage of women initiating breastfeeding ranged between 84% and 99% in rural and urban populations. For the purpose of this article, the data originally categorized as urban by PérezEscamilla were separated into urban and metropolitan, defining metropolitan as cities of more than one million inhabitants during the year the studies were conducted. This distinction is relevant because of differences in rural-tourban migration rates and in the availability and accessibility of health care services. As seen in table 1, breastfeeding prevalences at birth varied widely among rural (73% to 99%), urban (79% to 94%), and metropolitan (59% to 86%) populations. Urban and metropolitan populations tended to have lower prevalences of breastfeeding. The prevalence was progressively lower at three and six months postpartum in the three categories. The most notable reduction occurred in the urban and metropolitan groups. The wide variability in the prevalence might be attributed to differences in the operational definitions of breastfeeding, differences in sampling procedures, and the extreme differences in the sample sizes of the referred series (median, 105 subjects; range, 50 to 5,011).

A more reliable picture might be obtained from three nationwide studies [6-8]. The proportion of never-breastfed infants in the 1986 National Health Survey in the 32 Mexican states [6] ranged from 5% to 34% (median, 21%). Another study, representing all geographic regions and both urban and rural populations, found an overall prevalence of breastfeeding in the first months post-partum varying from 60% among the urban elite to 89% in rural populations [7]. These figures dropped to 18% and 54%, respectively, at six months. The National Nutrition Survey of 1988, based on a probabilistic sample, reported that 13.8% of infants younger than four months never received breastmilk, while 60% were fed breastmilk for at least four months, but only 11.5% were exclusively breastfed for this period. They found significant regional differences in the prevalence of breastfeeding and determined in a hazard analysis that better living conditions (a proxy for socio-economic situation), higher levels of maternal education, introduction of other milks, and living in urban municipalities were detrimental to breastfeeding. Data about exclusive breastfeeding, defined as being fed breastmilk but no other milks or liquids, were available in only two series [7-9]. The prevalence of these feeding categories at one month postpartum was 19% (7) and 23% (8, 9), and at three months, 0% and 3%.

Surveys conducted after the Baby-Friendly Hospital Initiative was launched indicate that the prevalences of breastfeeding and exclusive breastfeeding are increasing. In metropolitan Mexico City, the initiation of breastfeeding was reported as universal [10]. Within the first month postpartum, breastfeeding prevalence was 76%, with an 11% rate of exclusive breastfeeding; at four months post-partum, the rates fell to 57% and 4%, respectively. Preliminary data from a larger study conducted in 36 public and private hospitals in 1994 and 1995 showed that before hospital discharge, the overall prevalence of breastfeeding was 87%, and the prevalence of exclusive breastfeeding was 70% (E. Rios, personal communication, 1995). Another study combining data from mother-infant pairs participating in a breastfeeding promotion programme and data from controls reported a 93% prevalence of breastfeeding at one month post-partum, falling to 74% at four months post-partum. No data on exclusive breastfeeding were available [11].

TABLE 1. Median (range) prevalence of breastfeeding according to residence and age of child in the series reviewed by Pérez-Escamilla and Dewey [5]a

Age Rural Urban Metropolitan
No. series % breastfeeding No. series % breastfeeding No. series % breastfeeding
Birth 13 91
(73 -99)
9 85
5 66
3 mo 2 73.5
6 55
6 54
6 mo 9 77
4 52
6 36

a. The series represent samples or subsamples from individual geographic localities defined by the authors in each article.

Economics and national policies of breastfeeding

The manufacturers of infant formulas are frequently international enterprises. Their market interests go beyond formulas and even beyond specialized products for infants and children. In Mexico one manufacturer controls more than 75% of the infant formula produced within the country and more than 97% of the powdered formula. This almost monopolistic control gives manufacturers a great influence on market regulation [12, 13].

The International Code for Marketing Breastmilk Substitutes was adopted by the Mexican health authorities in 1989. Two years later, the Mexican Congress enacted the code into law. The Ministry of Health included the BabyFriendly Hospital Initiative in the National Plan for Health [14]. As a result, by the end of 1994, 15% of the 532 qualified hospitals in the country were awarded the title of Baby-Friendly Hospitals [15]. Before the Baby-Friendly Hospital Initiative was implemented in Mexico, formula and baby foods were advertised extensively and promoted heavily by hospitals, paediatricians, and nurses. A very high percentage of hospitals received free or reduced-price formula from manufacturers. Only 7 of 59 hospitals purchased all their formula, and only 2 paid full price [12]. Usually, hospitals were supplied by more than one manufacturer. In the majority of cases, hospital officers stated that such donations were unsolicited. In addition, manufacturers were allowed to distribute samples of formula to mothers at the time of hospital discharge. Mothers were approached outside the hospital premises in most cases, thus relieving hospitals from legal responsibility.

In 1993 all companies selling infant formulas in Mexico signed a voluntary landmark agreement committing themselves to stopping these practices. As a result, the report of the US Agency for International Development/Latin American and Caribbean Health and Nutrition Sustainability (USAID/ LACHNS) [16] found that distribution of free samples or gifts to mothers by formula companies almost vanished from the two hospitals surveyed. In a subsequent study of 36 hospitals conducted by Rios et al. (E. Rios, personal communication, 1995), officers from seven hospitals acknowledged accepting free or low-priced formula supplies.

Health-care Institutions

Perhaps the most contradictory aspect of Mexican healthcare institution policy related to maternal and infant health is the mandate by labour laws to provide mothers of infants a free six-month supply of a breastmilk substitute. In the past, conflicts within hospitals between the declared norm and the practice were frequent. In a survey of 59 hospitals in 1991, administrators claimed to have installed facilities and to have adopted routines favourable for breastfeeding. Nevertheless, investigators observed significant deviations from their claims [17]. For instance, none of the hospitals practiced early mother-infant contact. Although most claimed to have facilities for rooming-in, only 5% practiced it systematically. Most hospitals kept newborns in nurseries and provided mothers with portable cribs for the infants during the daily visits of the infants to the mothers' rooms. Infants were fed formula in the nurseries, having very few occasions to suckle at the breast. Only 4% of the hospitals allowed exclusive breastfeeding during the day; almost 16% did so during the night. The hospital schedules for breastfeeding were related more to staff shortages than to intentional policies. About half of the hospitals surveyed provided new mothers with written information about how to feed their babies at discharge. Although material encouraging breastfeeding predominated, it was astonishing to find that 20% of the hospitals provided information encouraging bottle feeding [17].

Preliminary data obtained by the follow-up study in 36 hospitals by the Nestle Infant Formula Audit Commission conducted by Rios from 1994 to 1995 (E. Rios, personal communication, 1995) provide evidence of a substantial improvement in those policies and practices. About half the mothers suckled their babies in their own beds, though only a small percentage were allowed to suckle within the first 30 minutes post-partum. About 80% of breastfeeding women had proper facilities in the hospital that enabled them to feed their infants throughout the day. At discharge 40% of the mothers reported they had participated in educational activities about breastfeeding, and 4% had received information exclusively about formula-feeding. The USAID/LACHNS report [16] found that elimination of infant formula from hospitals was a widespread practice, probably because breastfeeding is less time-consuming and produces substantial savings. In contrast, the implementation of other policies had less success. In two hospitals with full rooming-in, 40% to 60% of the infants were fed before the initiation of breastfeeding, most of them with oral glucose solutions. The funding for educational activities and counselling was low, and the intended educational messages were not conveyed efficiently.

A recent survey compared the performances of 14 public hospitals in Mexico City. Half were certified as Baby-Friendly Hospitals [18]. The evaluation was based on interviews with mothers on discharge from the hospital. The questionnaires explored the hospitals' policies related to the "Ten Steps to Successful Breastfeeding" [19]. Certified hospitals scored significantly better than noncertified hospitals in many areas: pre- and postpartum instructions on infant feeding, the numbers of infants suckled within the first 30 minutes of life, rooming-in, exclusive breastfeeding, non-use of feeding bottles, and availability of support groups. Encouragement from the health team to breastfeed was similar in both types of hospitals. Formula was prescribed for a negligible proportion of mothers. It must be underlined that despite the differences described, the non-certified hospitals have had a good level of compliance with the policies of the Baby-Friendly Hospital Initiative. The effect of rooming-in on the initiation of breastfeeding was compared in a cohort of 15,574 mother-infant pairs [20]. Sixty-eight per cent of the infants in the rooming-in programme breastfed within six hours after birth, and all were breastfeeding at discharge. None of the infants in the traditional wards did so. In spite of the shortcomings described, active breastfeeding programmes have a clear and positive impact on breastfeeding prevalence.

Another problem is the high proportion of Caesarean deliveries, which might interfere with the decision of women to breastfeed. A longitudinal study by our group [11] found that almost 30% of the women in a cohort delivered by Caesarean section. These figures are consistent with many other reports. Although women giving birth vaginally breastfed more frequently than those delivering by Caesarean section, breastfeeding rate differences vanished by 60 days post-partum, making it evident that rooming-in stimulates the initiation but does not lengthen the duration of breastfeeding.

Health professionals

There is a general notion that physicians and allied professionals in Mexico lack adequate skills to advise lactating women about initiating and sustaining lactation. Such a notion is based on the evidence that their knowledge of nutrition is very superficial [21]. Nutrition is not included in the curricula of medical schools as an individual discipline. The principles of infant feeding are taught in courses of paediatrics. The most popular textbooks of paediatrics have 3 to 6 pages of information on human lactation and 9 to 25 pages of information on artificial feeding, and comparable amounts of classroom time are devoted to these topics.

In a recent study more than 500 medical students and more than 170 residents from different Mexican universities answered a questionnaire exploring their knowledge of the basics of nutrition [22]. The critical grade for an appropriate level of knowledge was 4.3, which was higher than the average grade of the medical students and residents. In 1992 the National Centre for Maternal Lactation launched a programme to train health professionals in infant nutrition and breastfeeding. The Centre produced educational materials to support the future educational activities of those graduating from the Centre. There has been no published evaluation of this programme.

Individual beliefs

The multiple social factors that are important to the establishment of lactation vary among cultures. In Mexico regional differences often encompass significant cultural diversity. Such differences will be illustrated by data gathered from two independent cohorts of 346 urban and 216 rural mother infant pairs.

Communities studied

The rural setting is the Otomi Indian village of San Mateo Capulhuac north-west of Mexico City (n = 216). The 5,000 inhabitants live mostly from subsistence agriculture, with maize the main staple. There is little consumption of animal products. The diet of lactating women is marginal in energy and protein and low in fat. The level of physical activity is high [23].

The urban setting is represented by two neighbourhoods of Mexico City: Iztapalapa in the southeast (n = 170) and Tizapan in the south-west (n = 176). Both are densely populated by families of low-income workers living in small apartments. The diet of urban lactating women is closer to the Recommended Dietary Allowances [24] in energy and protein than that of rural women. Their lifestyle tends to be sedentary.

Besides the geographic differences, the two groups have significant differences in level of poverty, education, and accessibility to a paying job. There are also differences in sanitary facilities in the home. Although piped water was available in most rural households, it was not chlorinated, and fecal contamination was the norm (table 2).

In the rural community, 99% of the infants were predominantly breastfed in the first two weeks (other liquids could be provided except for non human milk). These high rates prevailed up to six months (table 3). None of the mothers failed to breastfeed their previous children, and all mothers reported being breastfed as infants. Formula was not commercially available in the village at the time of the study, although feeding bottles were present. The price of one can of formula in the nearest town was equivalent to one day's salary. The high prevalence of breastfeeding seems to have very strong cultural support, while formula-feeding was not practised for economic reasons. The breastfeeding rate was also high (93%) immediately after delivery in the urban group. It declined progressively in the post-partum period. By the third month fewer than threequarters of the women were providing any breastmilk to their infants, and only 40% of the mothers were predominantly breastfeeding. At the end of the sixth month, 52% of the mothers were feeding their infants any breastmilk, and only 25% were feeding breastmilk without additional nonhuman milk (table 3).

TABLE 2. Socio-economic characteristics of the communities

Characteristic Rural
(n = 216)
(n = 346)
Poverty level of the communitya 4 2
Household characteristics
piped water 93% 92%
flush toilet 6% 87%
dirt floor 64% 11%
refrigerator 5% 60%
crowdingb 91 % 80%
Maternal characteristics
education, median years (range) 3 (0-6) 9 (2-14)
living with partner 98% 87%
working outside home 2% 32%

a. 1 = mildest, 5 = worst (see ref. 24 for explanation of scale).
b. Three or more persons per room.


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