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STUDIES         OF       HUMAN             LACTATION                                                                      ...
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STUDIES     OF     HUMAN           LACTATION                                                                       749

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STUDIES                 OF     HUMAN               LACTATION                                                              ...
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STUD1ES            OF     HUMAN           LACTATION                                                                      7...
Clinical And Field Studies Of Human Lactation Methodological Considerations
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Clinical And Field Studies Of Human Lactation Methodological Considerations


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Clinical And Field Studies Of Human Lactation Methodological Considerations

  1. 1. 1 Original Research Communications-method Clinical and field studies of human lactation: methodological considerations13 Kenneth H. Brown, M. D. , Robert E. Black, M. D. , M. P.H. , Alastair D. Robertson, M. S., Naheed A hmed Akhtar, M. B. B. S. Md. , Giashuddin Ahmed, M. Sc., and Stan Becker, Ph.D. ABSTRACT A variety of studies has been completed to assess selected methods that are presently being used or might potentially be used to evaluate lactation performance. During 64 test-weighings of infants before and after the consumption of a known amount of milk. the mean Downloaded from www.ajcn.org by on August 22, 2009 ± SD “recovery” ofmilk ingestion was 94.9 ± 13.2%. The weight ofmilk extracted by a mechanical pump was approximately 7% greater than the amount measured during test-weighings of infants of the same women within periods of 1 wk. To evaluate the possibility of performing abbreviated studies in field settings, the proportion of24-h milk consumption received during 12 daytime hours was measured by test-weighings. Daytime consumption ranged from 46 to 58% of24-h consumption ( ± SD = 52 ± 3%). Attempts to predict the amount of milk consumption during 341 daytime studies from the age of infants and their frequency and duration of feedings met with limited success. Although each independent variable was significantly correlated with the amount con- sumed (multiple r = 0.69, p <0.001). the SE of the estimate (Sy.x) was relatively large. The effects of time of day and side of extraction on the volume and composition of extracted milk were determined during 24-h studies of seven women. There were significant changes in the concentration of fat (p < 0.001) and nitrogen (p = 0.003) during the day and significant differences in the concentrations of fat (p = 0.04) and lactose (p = 0.04) and in the volume (p < 0.00 1) of milk produced by each breast. The importance of these findings for the planning and interpretation of studies of human lactation is discussed. Am J Clin Nutr 1982:35:745-756. KEY WORDS Human lactation, breast-feeding, human milk, infant feeding Introduction From the Division ofGeographic Medicine (K.H.B., A. DR.), Department of Medicine, Gastroenterology and Nutrition Unit, Department of Pediatrics, School of Among mothers and scientists of the tech- Medicine, Division of Human Nutrition, Department of nologically advanced countries there has International Health, Johns Hopkins University, Balti- been a recent resurgence of interest in breast more, MD; the International Centre for Diarrhoeal Dis- feeding. Simultaneously, the World Health ease Research (Formerly The Cholera Research Labo- ratories) (K.H.B., R.E.B., SB.), Dacca, Bangladesh; the Organization, recognizing the central impor- Center for Vaccine Development (R.E.B.), University of tance of breast-feeding for the health of in- Maryland School of Medicine, Baltimore, MD: Save the fants in the developing world, has launched Children Fund (N.A.A., Md. GA.), U.K., Children’s a number of studies of present day breast- Nutrition Unit, Dacca, Bangladesh. 2Supported in part by USAID Grant DAN-l406-G- feeding practices and has stressed the need SS-l031-00. Supported by an International Center for for additional research in the physiology of Medical Research NIH Grant 5R07AI10048-17, by the lactation (1). Basic to the correct design and International Centre for Diarrhoeal Diseases Research, interpretation of such studies is the applica- Bangladesh (ICDDR,B) and by the Center for Vaccine tion of appropriate methodologies to investi- Development. Address correspondence to: Dr. Kenneth Brown. gate lactation performance in clinical and 615 North Wolfe Street, Baltimore, MD 21205. field settings. The current studies were com- Received February 23, 1981. pleted in an effort to assess some of the Accepted for publication September 22, 1981. The American Journal of Clinical Nutrition 35: APRIL 1982. pp. 745-756. Printed in U.S.A. 745 © 1982 American Society for Clinical Nutrition
  2. 2. 746 BROWN ET AL. procedures commonly used to evaluate lac- trict, Bangladesh, the rural setting ofa variety tation. of health-related activities of the Interna- The difference in an infant’s weight before tional Centre for Diarrhoeal Disease Re- and after nursing has been assumed to equal search, Bangladesh (formerly the Cholera the weight of milk consumed, but few studies Research Laboratory). The geographic, so- have attempted to validate this “test-weigh- cial, and demographic characteristics of the ing” technique or to compare it with other area have been described previously (2, 3). methods of estimating the production or con- The individual studies were performed in the sumption of human milk. Although simple to home of each study subject. perform in clinical wards, the test-weighing technique itself becomes impractical for 24-h Study subjects studies in field settings. Thus, more simplified Participants in the ward studies were re- or abbreviated techniques of investigation cruited from a large group ofwomen enrolled must be developed and evaluated. Further- in a social service program located in a more, the complete assessment of lactation “bustee” area (semiurban slum) in outlying performance must include some indication of Dacca. After learning of the purposes and the composition of nutrients in the milk, ne- design of the study, interested women were cessitating the extraction of a representative transported to the ward to visualize the study Downloaded from www.ajcn.org by on August 22, 2009 sample of the day’s production. Knowledge site; consenting subjects were then accepted of whether a given sample of milk is repre- for participation in future studies.4 The 61 sentative of the full day’s production requires women ranged in age from 14 to 39 yr (me- the analysis and comparison of levels of nu- dian 20 yr), were all primiparous except three trients in the milk at different times of the women, and were in good, general health. day. Specific studies were therefore under- None was using hormonal contraceptives at taken to address these issues in preparation the time of the study. Their infants’ ages for subsequent studies of lactation perform- ranged from 1 to 9 months. In return for their ance among relatively undernourished participation the subjects and their infants women of two communities in Bangladesh. received routine preventive and curative health services as well as remuneration in lieu Methods and results of potential earnings. The 13 infants taking part in studies designed to validate the test- Study sites weighing technique were selected from inpa- All ward studies were accomplished in an tients recovering from severe protein-calorie eight-bed metabolic ward situated at the Chil- malnutrition at the Children’s Nutrition Unit. dren’s Nutrition Unit (CNU) in urban Dacca, The village study subjects were selected Bangladesh. The ward was separated from from a group of mothers who were already the rest of the hospital, and the study room participating in a separate study of infants’ was furnished simply to appear more like a dietary intakes, and who were found to be village home than a hospital ward. The study particularly interested in and cooperative subjects nursed their infants openly, as is with the earlier investigations. The women customary in Bangladesh; no special nursing were 17 to 42 yr of age (median 25 yr), in areas were provided for the women. Meals good health and had from one to eight living were prepared for the mothers according to children (median three), including the nurs- fixed dietary protocols (to be described in ing infants who ranged from 6 to 29 months detail in subsequent communications); but of age. Several additional women (usually the women were responsible for basic relatives of field workers) were enrolled in housekeeping chores and for the care of their the studies comparing 12- and 24-h milk con- infants while staying on the ward. The sumption, since it was particularly difficult to mother-infant pairs stayed in the ward for as little as 2 days for “outpatient studies” and The research protocols were approved by the re- spective Committees on Human Volunteers of the School for as long as 6 wk for “inpatient studies.” of Hygiene, Johns Hopkins University, of the Cholera The village studies were completed in sev- Research Laboratory and of the Bangladesh Medical eral villages of Matlab Thana, Comilla Dis- Research Council.
  3. 3. STUDIES OF HUMAN LACTATION 747 arrange 24-h, home-based studies in the con- A minimum of nine validation studies was servative village society. completed by each ofthe six clinical assistants The methods and results of the individual responsible for the test-weighing of infants parts of the study will be presented together during longitudinal, clinical studies of lacta- to facilitate comprehension. A list of each of tion performance. The accuracy of the the individual studies, as well as their number “weighed-feeding” procedure, as determined and location is found in Table I. by the mean percentage of a known weight of ingested milk that could be measured by Validation of test-weighing technique test-weighings ranged from 89.4 to 98.6% for Quantification of infants’ consumption of the individual clinical assistants (Table 2). mother’s milk has traditionally been accom- The SDS ofthe recoveries ranged from 4.8 to pushed by the test-weighing technique. In the 24.4% for the different assistants. The mean present study, diapered infants were weighed ± SD overall recovery of milk ingestion dur- before and after feedings by a clinical assist- ing all 64 validation studies was 94.9 ± 13.2%. ant using a balance calibrated daily against The variation in the recoveries tended to be known weights. The diapers were covered by greater when smaller amounts of milk were plastic pants and were not changed until the consumed. second weighing was completed. The ward Fourteen similar studies of single feedings Downloaded from www.ajcn.org by on August 22, 2009 balance (Detecto Infant Scale) was sensitive were completed in the village subjects’ homes to 5 g; the balance used in field studies was to define the accuracy of the test-weighing a modified solution balance (Heavy Duty technique under field conditions. The recov- Solution Balance, Ohaus) sensitive to I g. ery of a known amount of ingested milk During the validation studies the infants were ranged from 56.2 to 117.8% in the field setting fed by spoon from cups of milk that had been with a mean ± SD of 88.6 ± 14.4%. preweighed by a second study assistant on a balance (Dial-O-Gram Balance, Ohaus) sen- Comparison of the weights of milk consumed sitive to 0.1 g. After the infants had been fed and the weights of milk extracted by the mother or by a study assistant other than the individual responsible for weighing In order to determine whether the two the infants, the cup of milk was reweighed. different methods of estimating the amount The infant’s weight change was then ex- of milk production provide similar data, val- pressed as a percentage of the change in the ues obtained from the same woman by test- weight of milk in the cup. Three studies were weighing and by mechanical extraction were eliminated from consideration because either compared over short intervals of time (less a sizeable amount of milk was spilled or the than 8 days). During the period of extraction baby regurgitated. all milk was extracted from both breasts by TABLE 1 Summary of methodological evaluations, locations of studies, and numbers of studies and subjects . . No. Of mothers Purpt.c of .tud Ltcatin ?So. of .tudie . or ntant Validation oftest-weighing . Urban ward 64 13 Rural homes 14 14 Comparison of test-weighing and mechanical extrac- Urban ward 167 72* tion Determination of density of milk Urban ward 511 60 Comparison of amount of milk consumed in 12- and Urban ward 250 28 24-h periods Rural homes 12 12 Prediction of human milk consumption from age of Rural homes 341 52 infant, frequency and duration of feedings Determination of changes in volume and composition Urban ward 7 of extracted milk by side of extraction and time of day * Mothers participating as both inpatients and outpatients are considered twice.
  4. 4. 748 BROWN ET AL. TABLE 2 Comparison of the change in infant weight before and after feedings with the weight of milk ingested Average amount of milk Average wt change of ‘Recovery of ingested milk by Clinical Assistant No of studies ingested infant weighed-feeding technique g g ‘: 1 10 160 147 91.1 ± 8.4* 2 9 113 109 89.4± 24.4 3 9 153 148 96.1±8.2 4 9 154 148 96.4 ±4.8 5 9 146 140 94.4 ± 9.8 6 18 142 141 98.6 ± 13.8 All studies 64 144 139 94.9 ± 13.2 * Mean ± SD. a mechanical breast pump (Egnell) at 3-h Density of extracted milk intervals and pooled for the 24-h period. Two To estimate the amount of milk consumed groups of women were studied during either by a single infant on multiple days, the least inpatient or outpatient periods in the clinical disruptive measurement procedure should be ward. During the 1 18 inpatient studies of 23 Downloaded from www.ajcn.org by on August 22, 2009 utilized. Although test-weighings are a more mother-infant pairs, the total amount of each suitable technique than extraction of milk, day’s test-weighings measured during some extraction would be necessary periodically to or all of the 6 days either before or just after determine the concentration of nutrients in a day of mechanical extraction was compared the milk. To estimate the infant’s consump- to the weight of that extracted milk. During tion of nutrients, one could then multiply the the 3-day outpatient studies of 49 mothers concentration of nutrients in extracted milk and infants, the data from the 2 days of test- by the amount of milk consumed on those weighings were compared to those for the days when nursings were weighed. This cal- intervening day’s extracted milk. Paired data culation assumes little day to day variation in were analyzed by substracting the test-weigh- the concentration of nutrients. ing data for a given day’s study from the Whereas test-weighings measure the respective extraction data for the same weight of milk consumed, the concentrations woman during the same study period. As of nutrients are generally expressed per units presented in Table 3, those mean differences of volume. The amount of milk measured were always positive and usually statistically during test-weighings must be divided by its significant during the inpatient studies. In density to calculate the volume consumed. other words, mechanical extraction yielded To learn whether the density of milk is con- slightly higher estimates of milk production stant for all women the weights and volumes than did test-weighings. The 3-day outpatient of extracted milk were compared during 5 11 studies yielded similar results, but the differ- separate 24-h ward studies of 60 women. The ences were smaller than those measured dur- mean ± SD density for all studies was 1.036 ing the inpatient studies. Whereas the mean ± 0.017 g/ml, the grand mean for individual (± 1 SE) weight of extracted milk was 717 women was 1 .038 ± 0.01 1 g/ml. There was (± 21) g, the weight of milk measured by test- no statistically significant correlation between weighings averaged 7 14 (± 1 8) and 678 (± I 8) maternal age or infant age and the density of g, respectively, on the day before and the day extracted milk. after extraction. Only the difference on the day after extraction was statistically signifi- Comparison of the amounts of milk consumed cant (p < 0.0 1 If the test-weighings ). from all during 12 and 24 h of the paired studies were corrected for the amount of underestimation as determined in Ideally, quantitative studies of milk con- the earlier recovery studies, the amount of sumption should take place in the subjects’ milk production as estimated by either test- homes with as little disruption as possible of weighing or extraction would be similar. the mothers’ routine activities and feeding
  5. 5. STUDIES OF HUMAN LACTATION 749 TABLE 3 Comparison of the amount of milk produced by individual women in 24 h, as estimated either by extraction of milk or by test-weighings, by day of test-weighing before or after day of “paired” extraction Day before or after extraction Study I 2 3 4 5 6 One day of extraction followed by 6 days of test-weighings Amount ofrnilk measured 715.8 695.8 694.2 716.0 708.9 704.4 during test-weighings (g/ day) Mean difference* 96.3t 70.3t 8 1 .9f 60. It 58.7t 68.8t SE ofdifference 26.0 14.6 16.2 17.8 16.8 15.8 No. of paired studies 26 50 55 55 49 51 Six days of test-weighings fol- lowed by I day of extrac- tion Amount of milk extracted in 694.5 7 12.3 7 10. 1 69 1 .4 689.3 729.7 paired studies Downloaded from www.ajcn.org by on August 22, 2009 Mean difference* 48.6t 29.5 33.Ot 5l.7t 46.8t 48.2 SEofdifference 12.1 15.1 14.4 13.2 12.6 28.5 No. of paired studies 63 60 63 63 57 20 a Mean difference between extracted amount less test-weighing amount during paired studies of individual women (g/day). t Paired t tests (p < 0.01). :1: Paired t tests (p < 0.001). patterns, and without potentially anxiety-pro- daytime ranged from 46 to 58% during mul- yoking changes in surroundings. However, it tiple studies of 28 individual women (mean is not logistically feasible nor socially accept- ±SD, 52 ± 3%). All but two of the SDs of the able to accomplish large numbers of 24-h proportions for studies within individual studies of milk intake in subjects’ homes, so women ranged between 3 and 10%. investigations taking place in the field must Prediction of the amount of milk consumption be abbreviated. Therefore, preliminary stud- ies comparing 12-h intakes to actual 24-h f rom age of infant andfrequency and duration offeedings intakes were undertaken to determine what proportion of the day’s total intake was con- Since the test-weighing technique is cum- sumed between 6 AM and 6 PM These 24-h bersome for field studies, an attempt was studies were completed in I 2 village homes made to identify a more easily obtainable and the data obtained were compared to data estimate of the quantity of milk consumed in from 250 studies of 28 women enrolled in the a 12-h period. During an 8-month period, ward studies. three hundred forty-one 12-h weighed feed- The proportion of the entire day’s intake ing studies were completed for 52 infants in that was ingested between 6 AM and 6 PM the field. The field assistants timed each com- ranged from 37 to 72% (mean ± SD, 53 ± plete feeding (both breasts) to the nearest 9%) in the 1 2 studies of village subjects. Since whole minute. The relationship between the the number of villagers who consented to the number and total duration of feeding, as well 24-h studies in their homes was limited, the as infant age (independent variables) and the proportions were also calculated for a sam- amount ofmilk consumed in 12 h (dependent pling of outpatients who were enrolled in the variable) was analyzed by stepwise multiple ward studies on at least 5 different days. The linear regression (4) with the hope of iden- woman-specific mean proportions of the full tifying independent variables that accurately day’s intake that were consumed during the predict the amount of milk consumed.
  6. 6. 750 BROWN ET AL. The infant’s age, the frequency of feedings, when all three were considered simultane- and the total amount of time at the breast ously (multiple r = 0.69), they were together were significantly correlated with the amount able to explain only about 50% of the varia- of milk consumed (Tables 4 and 5). The age tion in milk consumption. The SE (Sy.x) of of the infant was negatively correlated with the estimate of the amount of milk consumed the frequency of feeding (r = -0.2 1 ), the by an individual was 81.8 g. Therefore the amount of time nursing (r = -0.2 1), and the 95% confidence limits of the estimate was ± amount of milk consumed (r = -0.34). The 54.8% ofthe mean amount ofmilk consumed. number of feedings and time at the breast were both positively correlated with the Composition and volume of milk extracted amount of milk consumed (r = 0.63 for both) from both breasts during 24 h and with each other (r = 0.82). Although the In order to determine an optimal sampling ability ofthe independent variables to predict procedure for measuring the concentration of the amount of milk consumed was enhanced nutrients in and the volume of extracted hu- TABLE 4 Amount of mother’s milk consumed (g) during 12-h studies by age of infant, total amount of time s uckling, and frequen cy of nursing Downloaded from www.ajcn.org by on August 22, 2009 Fre quency of feedi ngs (n/ I 2-h study) . Total time at O5 6-7 8+ All Ageoftnfant - breast Mean Mean Mean Mean n n n n amount amount amount amount 6-Il 0-59 11 224* 1 274 0 12 228 60-89 2 402 24 333 10 410 36 358 90+ 0 4 402 8 453 12 436 Total 13 252 29 340 18 430 60 348 12-17 0-59 47 228 5 287 2 328 54 237 60-89 9 318 35 343 16 328 60 334 90+ 2 261 3 370 19 414 24 396 Total 58 243 43 337 37 372 138 307 18+ 0-59 61 193 9 244 0 70 200 60-89 11 243 29 294 18 348 58 301 90+ 0 2 296 13 352 15 344 Total 72 201 40 282 31 350 143 256 All 0-59 119 210 15 260 2 328 136 217 60-89 22 288 88 324 44 355 154 327 90+ 2 261 9 368 40 402 51 390 Total 143 223 112 319 86 376 341 293 a Amount of milk consumed (g). TABLE S Results of multiple regression analysis relating age of infant, total amount of time suckling, and frequency of nursing (independent variables) to amount ofmilk consumed (dependent variable) during 12-h studies* (n = 341) Partial SD of partial Partial Independent Mean ± SD regression regres.ston F p variables coefficient coefficient )df= 1.337) <0.001 Age of infant (mo) 16.3 ± 4.9 -4.74 0.92 26.5 Amount oftime 66.0 ± 24.4 1.48 0.32 2 I.2 <0.001 at breast (mm) No. offeedings 6.1 ± 2.1 17.30 3.80 20.7 <0.001 Dependent Variable Amount of milk 292.7 ± I 12.3 consumed (g) ____________ ______________ a Multiple r = 0.668, SE (Sy.x) = 81.84, p < 0.00 I.
  7. 7. STUDIES OF HUMAN LACTATION 751 a Cu S t... 1 0 U 1t o > 1 2; . 8 #{149} t_ - 0 U Downloaded from www.ajcn.org by on August 22, 2009 E 8 , 0 - a U E - . a 0 0 , 0 1, 8 2 p.. #{149} O * a a ‘‘ E a E a § a z 0 #{149} 0 #{149} 0 p.. ,p *
  8. 8. 752 BROWN ET AL. man milk, milk was collected separately from Although the time-related changes for lactose each breast every 3 h during the course of concentrations and volume were not statisti- single 24-h studies of seven women. The vol- cally significant for the group as a whole, umes and weights ofthe milks were measured there were significant interactions between and well mixed aliquots were then stored at time and individuals for these two variables. -20#{176}C before analysis for nitrogen, lactose, In other words, there were statistically sig- and fat. Nitrogen concentration was deter- nificant diurnal changes in the concentration mined by a semimicro-Kjeldahl procedure of lactose (F = 3.38, p < 0.001) and volume (5) with an accuracy of 94.2 ± 8.4%, lactose (F = 1.80, p = 0.03) within individual subjects was measured by the method of Folin (6) but the times of those changes were not con- with an accuracy of 99. 1 ± 5.4% and total fat sistent for all individuals in the study group. was quantified gravimetrically after extrac- The magnitude of change in lactose concen- tion by the Rose-Gottlieb procedure (5) with tration was not great as the minimums were an accuracy of 100.5 ± 1.9%. greater than 90% of the maximums for all but The data for the concentration of nutrients one subject. However, some individuals had and the volume of milk were summarized to as much as a 2-fold difference in the volume determine changes related to the time of sam- of milk produced during different intervals of pling (Fig. 1) and side of extraction (Table the 24-h period. Downloaded from www.ajcn.org by on August 22, 2009 6). Analyses of variance (4) were then com- The differences between the volume of pleted as shown in Table 7. The time-related milk produced by the right and left breast differences were statistically significant in the were of statistical and biological significance case of nitrogen (F = 3.82, p = 0.003) and fat (Table 6). As a group the differences were (F = 5.30, p < 0.001). Whereas the minimum not great, but for some women the less pro- nitrogen concentration was slightly more than ductive breast yielded only 65% ofthe volume 90% of its maximum, the minimum fat con- of the more productive one. Although the centration was less than 65% of its maximum. concentrations oflactose and fat in milk from TABLE 6 Effects of side of extraction on concentration of nitrogen, fat, and lactose in, and volume of extracted breast milk from seven women Nitrogen concentration (mg/ . . Fat concentratton (g/dl) Lactose concentration (g!dl) volume (ml) dl Woman - Left breast Right breast Left breast Right breast Left breast Right breast Left breast Right breast 1 148 156 1.79 2.14 7.31 7.50 57 67 ±1 1* ±6 ±0.67 ±0.60 ±0.33 ±0.40 ±15 ±20 2 167 174 2.22 2.69 8.10 8.04 48 60 ±6 ± I1 ±0.88 ±0.74 ±0.3 1 ±0.27 ± 10 ±7 3 165 147 2.23 2.15 8.03 8.06 35 54 ±1 1 ±15 ±0.60 ±0.42 ±0.20 ±0.38 ±13 ±9 4 158 169 2.20 2.31 7.94 8.16 58 58 ±15 ±22 ±0.62 ±0.58 ±0.46 ±0.34 ±8 ±15 5 137 138 1.74 1.77 8.28 8.25 29 35 ±5 ±5 ±0.67 ±0.45 ±0.57 ±0.36 ±6 ±9 6 140 158 1.53 1.64 7.25 7.38 76 31 ±20 ±15 ±0.46 ±0.67 ±0.33 ±0.29 ±12 ±9 7 171 139 2.71 3.18 7.85 8.12 35 91 ±8 ±6 ±1.02 ±0.71 ±0.62 ±0.23 ±13 ±22 All 155 155 2.05 2.27 7.82 7.93 48 56 ±17 ±18 ±0.78 ±0.76 ±0.54 ±0.45 ±19 ±23 a Mean ± SD.
  9. 9. STUDIES OF HUMAN LACTATION 753 TABLE 7 Results of analysis of variance for volume and three components of extracted breast milk with factors, side of extraction, time of day, and interactions Factor Source ofvariation OF Mean Square F Significance Nitrogen Main effects Individual 6 1812 13.88 <0.001 Breast I 4 0.03 0.863 Time 7 498 3.82 0.003 2-Way interactions Individual xbreast 6 1286 9.86 <0.001 Individual x time 42 120 0.92 0.605 Breast X time 7 132 1.01 0.438 Lactose Main effects Individual 6 2.1 16 29.91 <0.001 Breast 1 0.323 4.56 0.038 Time 7 0.666 0.94 0.486 2-Way interactions Individual x breast 6 0.065 0.92 0.493 Individual x time 42 0.239 3.38 <0.001 Breast X time 7 0.102 1.44 0.214 Fat Downloaded from www.ajcn.org by on August 22, 2009 Main effects Individual 6 3.308 12.26 <0.001 Breast 1 1 .203 4.46 0.041 Time 7 1.430 5.30 <0.001 2-Way interactions Individual x breast 6 0. 195 0.72 0.635 Individual x time 42 0.505 1.87 0.023 Breast X time 7 0.162 0.60 0.753 Volume Main effects Individual 6 1880 15.91 <0.001 Breast 1 1930 16.34 <0.001 Time 7 106 0.90 0.5 19 2-Way interactions Individual x breast 6 35 1 1 29.72 <0.001 Individual X time 42 213 1.80 0.030 Breast X time 7 256 2.17 0.057 each breast were also statistically different, natural setting are most likely to estimate the the magnitude of those differences was rela- usual lactation performance with accuracy. tively unimportant when grouped data were The issues of cost, comfort of study subjects, analyzed. Even when individual women were and the level of technical sophistication re- considered, the differences between milk col- quired must also be considered in planning lected from each breast were not great, except such studies. for two women whose milk from one breast Test-weighing is the procedure used most contained about 80% of the concentration of commonly to estimate the amount of milk fat as compared to milk from the other breast. consumed by the nursing infant. The proce- dure is technically simple, requires minimal Discussion equipment and training of personnel, and interferes relatively little with the usual proc- The evaluation of lactation performance is ess of nursing. However, since the amount of of fundamental importance to nutritionists milk consumed at a single feeding may be concerned with the health of infants and their small, the measurement error can introduce mothers, particularly in the lesser developed variability that is a sizeable proportion of the countries. The techniques for such evaluation amount consumed. Nevertheless, in the pres- are limited by the central dilemma that the ent studies the mean recovery of a known impact of the study procedures themselves on amount ofingested milk attained a fair degree lactation remains uncertain. At best, one can of accuracy, even under field conditions, if compare a variety of techniques and assume multiple studies were undertaken. The test- that those procedures that are least invasive weighings consistently underestimated the and that require the fewest changes from the amount of milk consumed, probably because
  10. 10. 754 BROWN ET AL. small amounts of milk were spilled or regur- can be weighed during a 12-h period rather gitated. Insensible water loss of the infant than during a complete 24-h period. On the between weighings undoubtedly also ac- average, approximately 52% of the 24-h in- counts for some of the underestimation. Fi- take was consumed during the daytime pe- nally, any urine or stool passed after the nod by infants of mothers from our popula- initial weighing and inadvertantly not in- tions, both in field and ward studies. Al- cluded in the fmal weighing would also re- though there was considerable within and duce the recoveries. The range of variability between subject variability in the proportion of the technique also depends on the care of milk consumed during daytime hours, that with which the clinical assistants perform variability could be reduced by performing their tasks. In the present studies some assist- multiple studies. Whether such abbreviated ants were clearly superior to others in that studies are acceptable depends on the nature regard. and the design of research proposed. Field The test-weighing procedure has been studies of lactation performance that were compared to other methods of estimating completed in rural West Africa used a similar milk production in previous studies. Coward technique of 12-h test-weighing to estimate et al. (7) found that their technique of isotope milk consumption (10). In those studies, dilution by breast milk ingestion yielded which took place between 7 AM and 7 PM, Downloaded from www.ajcn.org by on August 22, 2009 higher estimates of milk consumption than less than 50% of the full day’s intake was weighed-feedings in six infants. In the present consumed during the 12-h studies. The dif- study we found that extraction of milk by the ferences in the proportions consumed during mechanical pump yielded an estimate of milk daytime hours may relate to the fact that a production that was about 6 to 7% higher different 12-h interval was studied or may than that measured by test-weighings within indicate culture-specific differences in breast- the same week. Hytten (8) also found that feeding practices. It would seem necessary to mechanical extraction yielded 6% more milk estimate the conversion factor directly for any than the sum of weighed feedings plus man- population to be studied by an abbreviated ual extraction of residual milk in studies that technique. took place on consecutive days (8). It is pos- The attempt to estimate milk consumption sible that mechanical extraction recovers by indirect methods was generally unreward- more milk than is actually consumed by the ing in that the majority ofvariability in intake infant or that test-weighings systematically data was unexplained by the independent underestimate the amount of milk produced. variables chosen. Unless better explanatory Since the difference in the estimates obtained variables can be identified we believe that the by the two techniques was similar to the estimation of milk ingestion of an individual difference between test-weighings and actual must continue to rely on a more direct tech- consumption observed during the “recovery nique of assessment, such as those techniques studies,” the latter hypothesis seems more mentioned above. However, similar indirect likely to be correct. techniques may be of value in estimating the In order to determine the density of human amount of milk consumption by a group of milk, the volumes and weights of multiple infants from a given population. Again, the extracted samples were measured. The spe- usefulness of the technique will depend on cific gravity of human milk has been reported the purpose of the data collection. The mu!- (9) as 1.032, which is similar to the present tiple regression analysis was of additional findings. Since the densities did not change interest in explaining some of the factors with infant or maternal age for our sample, affecting lactation performance in Banglade- most of the variability appears to be ex- shi mothers. For example, milk intake tended plained by individual differences and mea- to decrease as the infants became older. In- surement error. Therefore, when correcting creased total duration of suckling and fre- milk weight to volume or vice versa it would quency of feedings were both independently be preferable to use the conversion factor as associated with higher levels of milk con- determined for the woman in question. sumption in children of all ages. This latter To facilitate the collection of data on lac- finding is at odds with the results of the West tation performance in field studies, feedings African studies reported by Whitehead et a!.
  11. 11. STUD1ES OF HUMAN LACTATION 755 (10). Although they stated that the variation influence the concentrations of’ f’at and nitro- in total milk intake between individuals at gen in opposite directions. Nims et al. (13) any given age could not be explained by the also reported that maximal fat and protein frequency of feedings, they did report that concentrations generally occurred at different the amount ofmilk intake fell with infant age times of day, but the actual values were not and was accompanied by a gradual reduction presented. The differences in the productive in the frequency of feedings. We cannot ex- capacity ofthe two breasts were most impres- plain the differences in these two sets of data. sive for volume and fat concentrations. Be- The primary concern of nutritionists inves- cause the differences in volume were so great tigating lactation performance is to determine it appears that milk must be extracted from the total amount of nutrients ingested by the both breasts if the extraction data are to be infant and simultaneously lost by the mother. used as estimates of the volume of milk pro- Both the volume of milk consumed and the duced. However, the concentrations of nutri- concentration of nutrients in that milk must ents in milk from each breast were not very be measured. Since it is the entire day’s milk dissimilar, especially if data from a group of that is of interest, the milk that is collected subjects are of interest. However, if the con- for laboratory analysis must be representative centration of milk fat from individual sub- of the whole day’s production. The technical jects is the object of study, specimens should Downloaded from www.ajcn.org by on August 22, 2009 difficulties that interfere with the accurate be obtained from both breasts. Recently, Hall measurement of milk nutrients have been (16) reported that the concentrations of fat in discussed by Hytten and Thomson (I 1) who the fore-milk and hind-milk from the breast concluded that “there is no escape from the suckled second in the course of a nursing are necessity to obtain complete 24 hour samples greater than in the respective fractions from if misleading measurements are to be the breast suckled first. Unfortunately, we avoided.” Hytten (12) also claimed that milk did not record which breast was extracted must be collected from both breasts since first in our own studies. It is possible that the substantial differences may exist in the vol- differences observed between breasts reflect ume and composition of milk from each consistent biases in which breast was pre- breast. sented first for extraction. The data from the present study are con- Several recent publications have reviewed sistent with Hytten’s claims, but some quali- the numerous proven and theoretical advan- fications are justified. Although the concen- tages of breast feeding ( 17, 18). Because of trations of macronutrients in milk changed our interest in the nutritional well-being of significantly throughout the day, particularly children and their mothers, particularly in when individuals rather than groups were the lesser developed countries, we have re- considered, only the changes in fat concentra- cently undertaken studies of the lactation tions were of relatively great magnitude. If performance of marginally nourished women one were interested only in lactose concentra- in Bangladesh. The present methodological tion, for example, a randomly obtained sam- evaluations were initiated in an effort to de- ple would not be too misleading in that its termine the appropriate techniques for those lactose concentration would probably be less investigations. The data reported should be than 5% different from the daily mean con- of similar use to other individuals planning centration for that individual. The time-re- studies of human lactation or evaluating data lated changes in fat concentration that were from such research. observed in this study are consistent with the The authors appreciate the collaboration of the staff findings of other investigators (13, 14) and of the Save the Children Fund, U.K., Children’s Nutri- emphasize the necessity of complete collec- tion Unit, and the efforts of the field workers of the Matlab Research Area. We also thank Drs. R. B. Sack, tions to assess the total daily fat (and energy) G. G. Graham, W. B. Greenough, and M. M. Levine for production accurately. On the other hand, support and advice during the planning and analysis of Lauber and Reinhart (15) reported variations these studies. The encouragement of M. R., M. B., S. B.. in the protein and lipid concentrations rang- and N. B. is also gratefully acknowledged. ing from 5 to 15% and chose to ignore those References differences in their study of women in the 1. Anonymous. WHO/UNICEF Meeting. Lancet Ivory Coast. The time of day appeared to 1979:2:841-3.