Maternal nutrition
The gross composition of breast-milk from women in developing countries is comparable with that of Western mothers, although the amount of milk pro-duced appears to be slightly less. The similarity in breast-milk production and the ability of mothers from poorer nations to undergo repeated, prolonged lactation is perhaps surprising considering that women in many developing countries apparently subsist on diets providing only 40 to 70 per cent of the energy intakes of well-nourished lactating western women (an average of 1600 cal/day compared with 2300 cal/day).lO
Nevertheless, comparison of well-nourished and deprived groups in the same country and observations on lactational output during seasonal decreases in food availability, suggest that poor maternal nutrition may be the cause of smaller breast-milk yields; and where nutritional intake is very low, milk composition may also be affected.
Numerous studies have sought to test this hypothesis experimentally by supplementing the mother's nutri-tional intake during lactation. Such intervention studies have yielded contradictory results which are difficult to interpret due to differences in study design, type and quantity of supplements and duration of supplementation. The evidence for 'feed the nursing mother, thereby the infant' is weak, since although two-thirds of the studies reported some improvement, the increase in milk yields was small and in two studies accompanied by a decrease in nutrient content.
Vitamin supplementation did appear to increase vitamin concentrations in breast-milk, but improve-ment of the maternal diet generally had little positive effect on energy, protein, fat and lactose concentrations in breast-milk. As a practical intervention to improve milk output and gross composition, supplementation of lactating mothers does not therefore seem to be cost-effective. 7
The lack of success of such interventions may have been because the amounts of supplements provided were not sufficient to increase dietary intake signi-ficantly, or because supplements were provided over too short a time. However, even in a long-term study carried out in the Gambia in which net energy intakes of lactating mothers were increased by 46 per cent (over 700 cal/day), and protein raised to well above the daily WHO recommended allowance (thus eradicating the energy and protein deficit during the 'hungry season'), the effect of supplementation on milk volume was negligible. The effects on composition were also small:
milk protein increased by 7 per cent but total energy showed no change (an 8 per cent increase in fat was offset by an 8 per cent decrease in lactose) Y Mothers did, however, derive some benefit from the supple-mentation programme in that they reported fewer ailments and greater 'well-being'.
The extra energy and protein provided in the form of supplements during the Gambian study did not appear to be used to increase milk production or substantially increase fat stores, since the average net weight gain of supplemented mothers was 1.8 kg, which if weight gain was due to deposition of adipose tissue, would account for only 7 per cent of the extra energy consumed.
It has been suggested that the ability of mothers on very low calorie diets to produce milk volumes only
Factors influencing breast-milk quantity and quality 155
slightly less than those of well-nourished mothers, may be due to raised maternal metabolic efficiency12 and preferential channelling of nutrients to the breast through elevated prolactin levels, and that when extra energy is provided, much is wasted through relaxation of metabolic efficiency. A reduction in physical acti-vity is also likely to be an effective method of adjust-ing to low energy intakes, but this did not appear to be the case in the Gambia, where lactating women were as active as non-pregnant, non-lactating women except during the traditional postpartum month of confinemen t.
The poor diets of women in many parts of the world are cause for concern, since there clearly are costs to functioning at such an extreme level of efficiency. Low energy intakes during pregnancy, for example, result in small babies, with all the attendant problems associated with low birth weight. However, since milk production does not seem to be strongly limited by maternal nutrition during the period of lactation, attention to mechanisms which control the infant's 'demand' for milk may offer an alternative approach to improving lactational ou tpu t.
Infant demand
Frequency of breast-feeding
Very large milk volumes, averaging 1000 ml/day (after adjustments have been made for the test-weighing method used) have been reported for Australian mothers who belong to breast-feeding support groups.
Wet nurses and mothers suckling twins also produce large quantities of breast-milk. It has been argued that such outputs are potentially achievable by any woman, provided that true 'demand-feeding' is practiced, i.e.
the infant feeds frequently and the breast is emptied at each feed. 9 Frequent feeding has been found to increase breast-milk output up to the first month of life and in populations where there is a wide range in the number of breast-feeds, infants who feed more frequently or suckle for longer consume more milk. The physiological basis for this effect appears to be that sucking stimulates secretion of prolactin, which in turn increases milk yield. 13
It is generally thought that limits to feeding do not occur in traditional 'demand-feeding' societies, where the timing and duration of feeding are supposedly dictated by the infant's demand rather than the mother's schedule. In reality, the baby's access to the breast may be limited by the mother's need to resume her usual work as the baby grows older, or by seasonal increases in farming activities. Thus, even in
tradi-156 Maternal health
tional societies, opportunities for breast-feeding during the daytime may be controlled by the mother. This may provide an alternative explanation for the decrease in milk outputs observed in some countries during the 'hungry' season; this is the time of heaviest farm work, when the mother is forced to spend much of the day away from her child.
In many traditional societies the infant has free access to the breast at night since mother and infant sleep side-by-side. Night-time feeding is then more under the control of the infant, and as the amount of milk taken during the daytime decreases, night-time feeding makes an increasingly important contribution to total breast-milk intake as the infant grows older. 18 In industrialized countries, however, night-time milk intake decreases with increasing age due to the practice of cutting out night-feeds to ensure an uninterrupted night's sleep for the mother. 2
Supplementary food
A further major influence on lactation is supplementary feeding. The timing of first introduction of supplements is very variable; in a study of nine countries, supple-mentary foods were commonly given well before the age of six months.2 Traditionally, supplements may be introduced at a particular age for cultural or religious reasons. In general, this would be part of the process of weaning the infant from breast-milk on to solid foods, during which a gradual decline in the number of breast-feeds is paralleled by an increase in the number of supplementary feeds. However, mothers may start to introduce supplements unusually early, or give breast-milk substitutes, if they feel that their infant is not growing well or that their milk supply is no longer suffi-cient to supply the baby's needs, for example, if the baby appears to be hungry after breast-feeding.
In this case, supplementary foods should ideally contribute extra nutrients to those received from breast-milk. However, some studif"s have shown that young infants receiving supplements consume less breast-milk than exclusively breast-fed infants of the same age, and that when the number of supplementary feeds is increased, the number of breast-feeds decreases.
Rather than truly supplementing breast-feeding, early feeding of supplements may only substitute for breast-feeds, perhaps a deliberate policy by the mother to release her from breast-feeding, and so permit her to resume work activities. If supplementary foods are of poor nutrient quality and low energy density, there is a danger that total nutrient intake will fail to meet the needs of the growing infant, leading to malnutrition.
The early replacement of breast-feeds by bottle-feeds
or supplements may decrease milk intake and eventually reduce milk production, since the suckling stimulus which maintains milk synthesis will be diminished. A downward spiral of reduced milk production encourag-ing greater use of supplements and consequently even further reduction in milk output may result.
Infant size
If the baby has free access to the breast, and maternal milk production is not limited, intake will depend on the infant's appetite. Correlational studies have shown that larger (heavier) infants consume more milk than smaller infants of the same age, and that among young infants, those who were heavier at birth consume more than infants of lower birth weight. However, the direction of such associations is not clear: larger infants may have bigger appetites and be better at withdrawing milk from the breast; alternatively, consumption of more milk may result in a heavier infant. A second possibility is that the association between milk intake and infant weight is due to maternal nutrition during pregnancy, which influences birth weight and might also affect subsequent lactation performance.
Morbidity
Providing that the mother does not deliberately reduce breast-feeding when the baby is ill, infections do not usually affect breast-milk intake, although intake of solid foods is often reduced. 14 Some infants may not be able to suck effectively if they are too weak and tire easily (e. g. due to malnutrition or cardiac disease) or if they are neurologically impaired. Such infants consume little milk, which is likely to result in decreased maternal milk production due both to inadequate stimulation of the nipple and inadequate removal of milk from the breast. Maternal anxiety about the health and well-being of the infant may also interfere with milk production by inhibiting the oxytocin-mediated milk ejection reflex.
Hormonal contraception
While breast-feeding confers a degree of protection against conception, the effect appears to be less pronounced in well-nourished mothers and cannot be guaranteed for the individual. 13 Breast-feeding mothers therefore still require advice on contraceptive methods, especially after the first two months of lactation.
High dosages of combined oestrogen-progesterone oral contraceptives have been found to depress milk yield and also decrease protein, fat, lactose, and
mineral content of breast-milk while low-dose progesterone-only pills do not appear to adversely affect lactation. Depot-medroxyprogesterone acetate (DMPA) is a long-acting injectable contraceptive widely used in developing countries. Doses of 300 mg given at six-month intervals appear to increase milk volume while decreasing fat, protein and calcium con-centrations.15 DMPA is also secreted into the breast-milk at concentrations approaching maternal plasma levels, but so far no adverse effects on infants have been reported. These results suggest caution in recommend-ing hormonal contraceptives. Where there is no alter-native to birth control by pharmacological means, low-dose progesterone-only pills are least risky, since concentrations in breast-milk are very low, and there are no apparent effects on lactation.