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Nutrition During Lactation
4
Nutritional Status and Usual Dietary Intake of Lactating Women
As a first step in the process of describing the nutritional status of lactating women in the United States, the subcommittee evaluated the methods used to assess the nutritional status of lactating women as well as anthropometric and biochemical data from apparently well-nourished lactating women. It also conducted a detailed review of the information on dietary intake by lactating women in the United States. The lack of nationally representative data on dietary intake and laboratory values of lactating women presented a substantial barrier to this effort.
Few lactating women have been included in the nutrition monitoring activities conducted by the U.S. Departments of Agriculture (USDA) and Health and Human Services (LSRO, 1989) (for example, only 59 of 2,910 women in the Continuing Survey of Food Intake by Individuals, core sample, wave 1, were lactating) (S. Krebs-Smith, USDA, Human Nutrition Information Service, personal communication, 1988). Thus, the lack of general knowledge about nutritional status in this population group is destined to continue for some time unless action is taken to obtain more data on this subject.
ASSESSMENT OF THE NUTRITIONAL STATUS OF LACTATING WOMEN
The subcommittee briefly reviewed the general reasons for assessing nutritional status, as well as the tools for doing so, and their suitability for application to lactating women. It also identified purposes for which new tools may be necessary and provided guidance on interim strategies for the assessment of
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Nutrition During Lactation
nutritional status among lactating women. These are all discussed below along with a summary of the normative data that are available on the nutritional status of well-nourished lactating women.
Reasons for Assessing Nutritional Status Among Lactating Women
In general, assessments of the nutritional status of lactating women and other groups have many applications—in research, in patient management, in public policy development, and in program planning and evaluation. The selection of the indicator of nutritional status to be used should consider its intended application (Habicht and Pelletier, 1990).
To date, there have been few efforts to develop indicators specifically for the assessment of nutritional status among lactating women (Rasmussen and Habicht, 1989). Most indicators are normative; that is, they reveal how an individual's value for that indicator compares to some standard, usually derived from a population of normal, healthy subjects. Values outside a range defined by designated cutoff points are called abnormal, but may or may not be associated with any particular functional consequence. An example of a normative indicator is the comparison of weight for height or blood nutrient values to a reference standard. As discussed further below, no standards for anthropometric or biochemical indicators have been established for nutritional status among lactating women. The usefulness of values obtained from nonpregnant, nonlactating women as a reference standard for lactating women requires evaluation.
There are few indicators of risk of undesirable outcomes for lactating women. Instead, the risk is usually related to the health of the nursing infant. An example of such an indicator is an abnormally low concentration of riboflavin in milk, which is associated with the likelihood of nutritional deficiency in the nursing infant (Bates et al., 1982). Another is the classic association of low thiamin concentrations in the milk of mothers in a rice-eating population with a high incidence of infantile beriberi among breastfed babies (Kinney and Follis, 1958). In contrast, indicators of poor nutritional status with respect to certain micronutrients (e.g., iron) are well understood in lactating women and can be used for the targeting of nutrient-specific interventions.
Indicators of benefit (ways to identify lactating women who would benefit from a planned intervention) have yet to be developed. These would be the most useful indicators for targeting interventions. The theoretical work needed to develop indicators of benefit from interventions designed to ameliorate protein energy malnutrition has been started in studies of young children (Rothe, 1988). It is clear from a supplementation trial conducted in The Gambia (Prentice et al., 1983; see Chapter 5) that the indicators of poor nutritional status used (residence in a low-income community characterized by seasonal decreases in milk volume or low weight for height) are inadequate for predicting who will
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Nutrition During Lactation
benefit (at least in terms of increased milk volume) from a program of general nutritional supplementation.
Use of Biochemical Indicators
The few investigations in which biochemical measures have been used to assess the nutritional status of lactating women have used values for nonpregnant, nonlactating women as reference standards. This approach makes the assumption that the interpretation of levels of vitamins, minerals, hormones, and metabolites is unaffected by lactation. For this to be true, plasma volume in lactating women must be the same as that in nonlactating women and remain stable over the course of lactation. These ideas about plasma volume are difficult to evaluate with the currently available data. Unfortunately, few researchers have investigated changes in plasma volume post partum (Brown et al., 1947; Caton et al., 1951; Taylor and Lind, 1979), and it is impossible to tell whether the subjects in those studies were lactating. The results of those studies suggest that even in nonlactating women, plasma volume remains elevated for weeks to a few months after delivery. The only study that compared the plasma volume of lactating and nonlactating women post partum (Donovan et al., 1965) confirmed the decrease in plasma volume from 3 days to 6 weeks after delivery and established that the magnitude of these decreases was the same in both groups. At 6 weeks post partum, values for the lactating women (53.6 ml/kg of body weight) as well as the nonlactating women (50.1 ml/kg) remained above those reported earlier by the same authors (Donovan et al., 1964) for nonpregnant, nonlactating subjects (46.1 ml/kg). Plasma volume values were higher at both times in the lactating subjects, but this difference was not statistically significant.
Changes in plasma volume during lactation have also been reported for various other species. In cows (Reynolds, 1953), sows (Anderson et al., 1970), rabbits (Tarvydas et al., 1968), and rats (Bond, 1958), plasma volume is greater in lactating than in nonlactating animals.
The findings concerning plasma volume in lactating women and animals make it clear that plasma volume does not return rapidly to prepregnancy values. Thus, for this reason alone, it is probably inappropriate to assess the nutritional status of lactating women by comparing plasma nutrient values with reference values for a nonpregnant women, especially in the early postpartum period.
The assumption that blood values of vitamins, minerals, hormones, and metabolites are unaffected by lactation is known not to be correct. For example, insulin and glucose levels in lactating women respond quite differently to a test meal than they do in the same women after cessation of lactation (Illingworth et al., 1986). Protein metabolism also appears to change during lactation (Motil et al., 1989, 1990). Nitrogen balance among lactating women is lower than that among nonlactating postpartum and nulliparous women studied at similar
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levels of nitrogen intake. Differences in nitrogen balance are not accounted for by nitrogen losses in milk; urinary 3-methyl histidine excretion (a measure of muscle protein breakdown) also is lower in lactating women. Some changes in blood concentrations of vitamins and minerals over the course of lactation are unrelated to changes in plasma volume. For example, serum zinc concentration increases while serum copper decreases between weeks 1 to 2 and 19 to 21 of lactation (van der Elst et al., 1986).
In summary, evidence suggests that, in principle, it is likely to be inappropriate to compare blood values of various nutrients or metabolites of lactating women with reference values for nonpregnant women. However, the degree to which this approach misclassifies women's nutritional status depends on the degree to which levels in lactating women differ from those of their nonpregnant, nonlactating counterparts. As will be evident from the data summarized and discussed below, too few lactating women have been studied to make a meaningful evaluation of the validity of this approach at present.
Inferences about maternal nutritional status also can be made from the nutritional status of the infant. For example, infants with evidence of vitamin B12 deficiency (that is, those with increased concentrations of methylmalonic acid in their urine) may have mothers with poor vitamin B12 status (Specker et al., 1988). The reverse is not necessarily true, however. For example, the nutritional status of breastfed infants of mothers with inadequate folacin (Salmenperä et al., 1986) or vitamin C (Salmenperä, 1984) status may remain optimal. This issue is discussed further in Chapter 7.
Uses of Anthropometric Indicators
Tables developed by the Metropolitan Life Insurance Company have generally been used as normative standards for weight, height, and weight for height (MLI, 1959, 1983). For women in the United States, values derived from recent data from the National Center for Health Statistics (NCHS) (NRC, 1989) also could be used. There are drawbacks for both sets of values for studies of lactating women (Rasmussen, 1988). The use of such normative standards is fraught with all the problems discussed in Chapter 4 of Nutrition During Pregnancy, Part I: Weight Gain (IOM, 1990) as they relate to pregnant women. In particular, it is difficult to obtain accurate measurements without extensive training and monitoring, and comparison of a woman's values with either of these standards does not provide the information needed to make inferences about either the risk of adverse outcomes or the potential benefit from a nutritional intervention for the mother or the infant.
Many anthropometric indicators of nutritional status change continuously during lactation (Butte et al., 1984) and, even at 6 months post partum, may still differ from prepregnancy values (Sadurskis et al., 1988). The rate at which a woman (lactating or not) returns to her prepregnancy weight after delivery is
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affected by many factors. These include edema during pregnancy and the route of delivery (Dennis and Bytheway, 1965); prepregnancy weight, postpartum weight, parity, and maternal age (Brewer et al., 1989); and weight gained during pregnancy (Greene et al., 1988).
There is a need for research to develop indicators of nutritional status, analogous to those for weight gain during pregnancy, that make use of either the pattern or the total magnitude of the changes. Further research is also needed to investigate the use of other anthropometric indicators (e.g., various skinfold thicknesses or circumference measurements) for assessing the nutritional status of lactating women. Other approaches (e.g., bioelectrical impedance or isotope dilution [Wong et al., 1989]) for the evaluation of changes in body composition also merit study in lactating women.
Biochemical and Anthropometric Data from Well-Nourished Lactating Women
Biochemical Measures of Nutritional Status
Table 4-1 provides the biochemical measures of nutritional status from the few studies that have been conducted in lactating women and compares them with values for nonpregnant, nonlactating women. Also included are compiled values from presumably well-nourished lactating women living in industrialized countries. It is evident from Table 4-1 that data on a variety of biochemical measures of nutritional status have been collected for lactating women, but that the sample sizes range from only 3 to 36. Where comparison was possible, there was remarkably little difference between values for lactating women and those for nonpregnant, nonlactating women.
Blood Lipids
The blood lipid profiles of lactating women at 6 weeks post partum have been compared with those of parturient women who were not lactating (Knopp et al., 1985). The lactating women maintained lower total triglyceride and higher total cholesterol values than those in the nonlactating group. There also were statistically significant differences between the two groups in values for various lipoprotein lipids and apoproteins (Table 4-2). In contrast, both plasma cholesterol and triglyceride concentrations were higher at 8 weeks post partum than they were before conception among 14 lactating Swedish women (Fåhraeus et al., 1985). These studies suggest that lactation causes changes in lipoprotein metabolism.
Change in Body Weight During Lactation
Table 4-3 provides anthropometric measurements of nutritional status for lactating women and for nonpregnant, nonlactating women in the United States.
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TABLE 4-1 Biochemical Measures of Nutritional Status for Healthy Nonpregnant, Nonlactating Women and for Adults Not Receiving Supplements of the Nutrient Studied
Nonpregnant, Nonlactating Adults
Lactating Women
Measure of Nutritional Status
Mean or Rangea
Reference
Mean Value
Number of Subjects
Duration of Lactation
Reference
Macrominerals
Serum calcium, total (mg/dl)
8.8–10.0
Young, 1987
8.60 ± 0.17 SEMb
18;
3 wk
Greer et al., 1982
8.4–10.2
Tietz, 1986
9.59 ± 0.17 SEM
14
26 wk
Serum magnesium (mg/dl)
1.8–3.0
Young, 1987
1.95 ± 0.06 SEM
18;
3 wk
Greer et al., 1982
1.3–2.1c
Tietz, 1986
2.15 ± 0.07 SEM
14
26 wk
Trace elements
Plasma selenium (µg/liter)
NAd,e
Levander, 1988
136 ± 5 SEM
21
1 mo
Levander et al.,
137 ± 5 SEM
22
3 mo
1987
138 ± 5 SEM
22
6 mo
97 ± 6 SEM
10
4, 8 wk
Mannan and Picciano, 1987
RBCf selenium (ng/g of hemoglobin)
NAe
470 ± 33 SEM
20
1 mo
Levander et al.,
450 ± 33 SEM
21
3 mo
1987
501 ± 31 SEM
23
6 mo
173 ± 6.4 SEM
10
4, 8 wk
Mannan and Picciano, 1987
Plasma zinc (µg/dl)
88–123
NRC, 1978
79.1 ± 1.7 SEM
23
1 mo
Moser and
65–140
Solomons, 1988
87.6 ± 2.2 SEM
21
3 mo
Reynolds, 1983
84.4 ± 2.4 SEM
19
6 mo
70 ± 11 SDg
29
1 mo
Krebs et al., 1985
79 ± 10 SD
27
4 mo
Serum zinc (µg/dl)
75–120
Young, 1987,
73 ± 4.8 SD
10
5–75 days
Moore et al., 1984
70–150
Tietz, 1986
RBC zinc (µg/g)
NA
12.9 ± 0.2 SEM
23
1 mo
Moser and
12.0 ± 0.2 SEM
21
3 mo
Reynolds, 1983
10.7 ± 0.4 SEM
19
6 mo
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Nonpregnant, Nonlactating Adults
Lactating Women
Measure of Nutritional Status
Mean or Rangea
Reference
Mean Value
Number of Subjects
Duration of Lactation
Reference
Water-soluble vitamins
Erythrocyte transketolase activity coefficient
NA
1.07 ± 0.07 SD
10
5–10 wk
Dostálová, 1984
Urinary thiamin (mg/day)
NA
0.90 ± 0.46 SD
6
6 mo
Thomas et al., 1980
Erythrocyte glutathione reductase activity coefficient
NA
1.05 ± 0.14 SD
10
5–10 wk
Dostálová, 1984
Urinary riboflavin (mg/day)
NA
0.44 ± 0.23 SD
6
6 mo
Thomas et al., 1980
Erythrocyte oxaloacetate transaminase activity coefficient
1.69
NRC, 1978
1.75 ± 0.16 SD
10
5–10 wk
Dostálová, 1984
Plasma vitamin B6 (ng/ml)
3.6–18
Tietz, 1986
4.9 ± 2.4 SD
11
5–10 wk
Dostálová, 1984;
5–23
McCormick, 1988
8.4 ± 3.2 SD
NR
2 mo
Andon et al., 1989
Erythrocyte glutamic pyruvic transaminase activity coefficient
1.19h
NRC, 1978
1.17 ± 0.19 SD
6
6 mo
Thomas et al., 1980
Serum folate (ng/ml)
4.7–8.2
NRC, 1978
13.0 ± 3.13 SD
6
6 mo
Thomas et al., 1980
1.8–9
Tietz, 1986
3.8 ± 0.5 SEM
30
1 mo
Ek, 1983
5–16
Herbert and
4.1 ± 0.3 SEM
29
3 mo
Colman, 1988
4.3 ± 0.3 SEM
46
6 mo
4.8 ± 0.3 SEM
42
9 mo
4.6 ± 0.2 SEM
45
12 mo
8.6 ± 4.5i
8
5–10 wk
Dostálová, 1984
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Nutrition During Lactation
RBC folate (ng/ml)
165–250
NRC, 1978
124.4 ± 11.3 SEM
39
1 mo
Ek, 1983
128.5 ± 8.0 SEM
35
3 mo
130.1 ± 8.1 SEM
46
6 mo
136.3 ± 8.6 SEM
42
9 mo
136.3 ± 8.6 SEM
45
12 mo
Serum vitamin B12 (pg/ml)
458–498
NRC, 1978
692 ± 30 SD
6
6 mo
Thomas et al., 1980
100–700
Tietz, 1986
565 ± 184 SEM
8
5–10 wk
Dostálová, 1984
Plasma vitamin C (mg/dl)
0.87
NRC, 1978
0.55 ± 0.32 SD
6
6 mo
Thomas et al., 1980
0.6–2.0
Tietz, 1986
0.68 ± 0.27 SD
7
5–10 wk
Dostálová, 1984
Biotin (ng/liter)
NA
358 ± 64 SD
6
5–10 wk
Dostálová, 1984
Fat-soluble vitamins
β-Carotene (µg/liter)
600–2,000
Tietz, 1986
516 ± 203 SD
11
5–10 wk
Dostálová, 1984
Vitamin A (µg retinol/ liter)
550
NRC, 1978
546 ± 107 SD
11
5–10 wk
Dostálová, 1984
300–650
Tietz, 1986
408 ± 64 SD
17
20 wk
Ala-Houhala et al.,
490
Young, 1987
416 ± 56 SD
15
20 wk
1988
Retinol-binding protein (mg/liter)
NA
57 ± 12 SD
11
5–10 wk
Dostálová, 1984
Vitamin E (mg/liter)
8.9–12.3
NRC, 1978
11.8 ± 2.6 SD
11
5–10 wk
Dostálová, 1984
5.0–20
Tietz, 1986
a Range = Reference range from all sources except NRC, 1978; in that case it represents the range of means.
b SEM = Standard error of the mean.
c Higher in females during their menses.
d NA = Not readily available from standard references.
e No suitable clinical parameters.
f RBC = Red blood cells.
g SD = Standard deviation.
h Originally expressed as % stimulation.
i Measure of variance not reported.
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TABLE 4-2 Lipoprotein Lipids and Apoproteins for Lactating and Nonlactating Women 6 Weeks Post Partuma
Mean Value, mg/dl ± SDb
Type of Lipoprotein
Lactating Women (N = 56)
Nonlactating Women (N = 16)
Total
Triglyceridesc
92 ± 71
112 ± 56
Cholesterolc
207 ± 31
188 ± 29
Phospholipids
227 ± 29
217 ± 32
Apoprotein B
79 ± 29
69 ± 20
Very low density lipoprotein
Triglyceridesc
54 ± 67
78 ± 52
Cholesterol
14 ± 14
17 ± 11
Phospholipidsc
16 ± 17
24 ± 16
Apoprotein B
3 ± 3
4 ± 2
Low-density lipoprotein
Triglycerides
26 ± 12
24 ± 9
Cholesterol
129 ± 31
121 ± 30
Phospholipids
70 ± 21
70 ± 26
Apoprotein B
76 ± 28
66 ± 20
High-density lipoprotein
Triglycerides
12 ± 5
10 ± 4
Cholesterolc
65 ± 15
51 ± 8
Phospholipidsc
141 ± 22
123 ± 20
Apoprotein A-Ic
142 ± 23
126 ± 19
Apoprotein A-IIc
34 ± 6
31 ± 3
a From Knoop et al. (1985) with permission.
b SD = Standard deviation.
c Significant difference (p < .05) between lactating and nonlactating subjects.
These measurements (like those for biochemical indicators) have been reported for very few women at any stage of lactation. Two longitudinal studies (Butte and Garza, 1986; Butte et al., 1984; Manning-Dalton and Allen, 1983) and one abstract (Heinig et al., 1990) provide the data base for examining anthropometric changes during lactation. These data reveal a consistent average rate of weight loss of 0.6 to 0.8 kg/month during the first 4 to 6 months post partum, although mean weight early in lactation differed among the groups of women studied (Figure 4-1). Heinig and colleagues (1990) followed lactating women longitudinally for 12 months and found that, on average, weight loss continued between 6 and 12 months post partum, but at a slower rate than that in the first 6 months.
Not all the lactating women studied lost weight post partum; for example,
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Nutrition During Lactation
FIGURE 4-1 Change in maternal body weight during lactation. Means with standard error of the mean are illustrated.
in the study of Manning-Dalton and Allen (1983), 22% actually gained weight during breastfeeding. In an investigation of weight change in the 12 months after delivery among 1,423 Swedish women who attended maternity clinics, Öhlin and Rössner (1990) observed that lactation score (a measure of the intensity and duration of breastfeeding) was only very weakly (R = -.09) but significantly (p < .01) correlated with weight loss in this period. A stronger relationship between lactation score and weight loss was found between 2.5 and 6 months post partum. The authors concluded that ''lactation has no general clinical importance for post partum weight loss for the majority of women, and cannot be practically used as a predictor for weight development after delivery" (Öhlin and Rössner, 1990, p. 172).
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TABLE 4-3 Anthropometric Measures of Nutritional Status for Healthy Nonpregnant, Nonlactating Women and for Lactating Women in the United States
Nonpregnant, Nonlactating Women
Lactating Women
Measure of Nutritional Status
Mean
Reference
Mean ± SDa
Number of Subjects
Stage of Lactation
Reference
Overall body size
Weight (kg)
62b
Frisancho, 1984
63.7 ± 10.1
27
2 wk
Manning-Dalton and Allen, 1983
63.1 ± 10.1
4 wk
62.3 ± 10.3
8 wk
61.7 ± 9.8
12 wkc
61.3 ± 9.5
45
1 mo
Butte and Garza, 1986
60.7 ± 10.0
2 mo
60.2 ± 10.4
3 mo
59.3 ± 10.5
4 mo
Height (cm)
163
Najjar and Rowland, 1987
163.0 ± 6.3
45
NA
Butte and Garza, 1986
Body mass index (kg/m2)
23.1 ± 4.7 SD
Najjar and Rowland, 1987
23.0 ± 2.6
45
1 mo
Butte and Garza, 1986
22.8 ± 2.8
2 mo
22.5 ± 3.0
3 mo
22.2 ± 3.0
4 mo
Skinfold thickness (mm)
Triceps
23
Frisancho, 1984
19.8 ± 6.6
27
2 wk
Manning-Dalton and Allen, 1983
21.1 ± 6.7
12 wkc
16.9 ± 4.6
1 mo
Butte and Garza, 1986
17.0 ± 4.7
45
2 mo
17.3 ± 5.3
3 mo
17.2 ± 5.2
4 mo
Biceps
NAd
8.3 ± 5.2
27
2 wk
Manning-Dalton and Allen, 1983
8.0 ± 4.9
12 wkc
6.9 ± 3.2
45
1 mo
Butte and Garza, 1986
6.9 ± 3.3
2 mo
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ManningDalton and Allen 1983l
0.5
12
2,165 ± 757
95 ± 20
NR
NR
NR
NR
NR
NR
NR
NR
1
12
2,337 ± 593
87 ± 20
NR
NR
NR
NR
NR
NR
NR
NR
2
12
1,951 ± 749
81 ± 30
NR
NR
NR
NR
NR
NR
NR
NR
3
12
2,171 ± 749
90 ± 27
NR
NR
NR
NR
NR
NR
NR
NR
Stuff et al., 1983
Mixed
40
2,028 ± 357
84.5 ± 22.4
1,004 ± 413
1,385 ± 399
13.0 ± 3.0
NR
NR
NR
NR
NR
Butte et al., 1984
1
43
2,334 ± 536
98 ± 28
1,219 ± 543
1,722 ± 553
16.2 ± 4.8
9,070 ± 5,920
1.9 ± 0.9
2.6 ± 1.1
23.6 ± 8.4
150 ± 90
2
44
2,125 ± 582
91 ± 23
1,030 ± 466
1,496 ± 456
14.1 ± 3.7
8,532 ± 5,341
1.5 ± 0.6
2.1 ± 0.7
20.3 ± 5.8
124 ± 89
3
40
2,170 ± 629
89 ± 25
1,024 ± 478
1,467 ± 459
13.9 ± 4.0
7,598 ± 4,807
1.5 ± 0.5
2.1 ± 0.8
20.5 ± 7.2
114 ± 81
4
40
2,092 ± 498
87 ± 20
1,009 ± 460
1,465 ± 434
13.5 ± 2.7
7,126 ± 3,775
1.5 ± 0.7
2.1 ± 0.8
20.2 ± 5.9
115 ± 56
Song et al., 1985
Mixed
26m
2,014 ± 620
79 ± 26
1,243 ± 595
1,446 ± 563
26 ± 24
9,627 ± 5,206
2.1 ± 1.1
2.8 ± 1.4
70 ± 90
199 ± 129
Strode et al., 1986
Mixed
14
2,316 ± 240
108 ± 21
NR
NR
NR
NR
NR
NR
NR
NR
Teenagers
Lipsman et al., 1985
Mixed
25
2,897 ± 699
115 ± 27
1,640 ± 601
2,005 ± 588
15.0 ± 3.8
5,995 ± 2,839
1.49 ± 0.44
2.88 ± 0.91
20.0 ± 5.0
156 ± 136
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Mean Daily Intake
RDA, Population Group, and Reference
Months Post Partum
Sample Size
Energy, kcal ± SDb
Protein, g ± SD
Calcium, mg ± SD
Phosphorus, mg ± SD
Iron, mg ± SD
Vitamin A, IUc ± SD
Thiamin, mg ± SD
Riboflavin, mg ± SD
Niacin, mg ± SD
Ascorbic acid, mg ± SD
Vegetarians
Finley, 1985
Mixed
29
2,158 ± 601
78 ± 28
1,303 ± 611
1,736 ± 605
16.8 ± 6.9
9,756 ± 6,149
1.80 ± 1.02
2.15 ± 0.91
15.4 ± 6.5
175 ± 137
American Indians
Butte and Calloway, 1981
1
23
2,190 ± 990
87 ± 38
718 ± 458
1,270 ± 559
15.2 ± 5.9
5,467 ± 10,002
1.39 ± 0.69
1.81 ± 1.07
20.1 ± 9.1
150 ± 165
a Nutrients listed in this table are those most commonly included in nutrient data bases.
b SD = Standard deviation.
c IU = International units.
d NA = Not applicable.
e Calculated as the recommended daily energy increment for lactation (500 kcal) plus the energy allowance for females 11 to 50 years of age (2,200 kcal).
f Standard deviation not applicable to the RDA.
g Units for the RDAs are micrograms of retinol equivalents (RE); this is equivalent to approximately 5 IU of vitamin A obtained from the typical U.S. diet in the form of retinol (from animal products) and carotenoids (from plants) (Olson, 1987).
h NR = Not reported.
i Women taking supplements; intake from food only.
j Women taking no supplements.
k Standard error of the mean.
l Women in the study who averaged 95% lactation over the entire lactation period.
m Given as N = 46 for 26 subjects studied twice.
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variability is, however, of concern. Clearly, there were individuals within these samples whose dietary intake was either lower or much higher than the mean.
There is much less information concerning the adequacy of dietary intake of other micronutrients, as illustrated in Table 4-6. For example, iodine and vitamins E and K were omitted from the table because no relevant studies included them. Of the micronutrients reported in Table 4-6, vitamins B12, B6, and folate were the only ones studied by more than one group of investigators. The scant data do suggest closer examination of the adequacy of intake of folate and zinc, which were well below the 1989 RDAs in two studies, and of vitamin B6, which was consistently below the 1989 RDA. Clearly, research is needed to provide a more complete nutritional profile of lactating women.
Data from Various Population Groups
The subcommittee identified only two studies focusing on groups of lactating women defined by factors of culture, ethnic background, life-style, or religion. These were studies of American Indians (Butte and Calloway, 1981) and of vegetarians (Finley et al., 1985) (see Tables 4-5 and 4-6). Among American Indians, vitamin A intake was highly variable and intakes of calcium; magnesium; zinc; and vitamins D, E, and folate appeared to be low. Among all the studies for which results are shown in Table 4-5, mean protein intake was lowest in the vegetarian group but still exceeded the RDA. As expected, the mean vitamin A intake of the vegetarians was the highest. The subcommittee identified only one study of lactating teenagers (Lipsman et al., 1985) and none of lactating women over age 35. The teenagers were found to have mean dietary intakes that met or exceeded the 1989 RDAs (Table 4-5).
Data on the dietary intake of lactating women of low socioeconomic status were also difficult to find. The first national evaluation of the Special Supplemental Food Program for Women, Infants, and Children (WIC) included 179 postpartum women. Of these, less than 79% were breastfeeding at the time that dietary data were collected (at enrollment in WIC, approximately 12 weeks post partum; breastfeeding was a prerequisite for enrollment for most of these women); unfortunately, those maternal nutrient intake values were not presented separately by breastfeeding status (Edozien et al., 1976). In general, the dietary intakes of these women were much lower than the current RDAs. Dietary intake of vitamins B6, B12, and folate was assessed in seven low-income women recruited from a WIC program (Sneed et al., 1981) (Table 4-6). At two stages of lactation, their reported intakes of vitamin B6 were well below the RDA but were comparable to the values for the other groups included in these tables.
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TABLE 4-6 Mean Daily Dietary Intakes of Selected Micronutrients by Lactating Women in the United States Compared with the Recommended Dietary Allowances (RDAs)a
Vitamin
Population Group and Reference
Stage of Lactation
D, µg ± SDb
E, mg ± SD
B6, mg ± SD
B12, µg ± SD
Folate, µg ± SD
Magnesium, mg ± SD
Zinc, mg ± SD
Selenium, µg ± SD
RDAs
NRC, 1989
0-6 mo
10c
12
2.1
2.6
280
355
19
75
7-12 mo
10
11
2.1
2.6
260
340
16
75
Well-nourished adult women
Thomas and Kawamoto, 1979
4-7 days
NRd
NR
1.69 ± 0.65
NR
NR
NR
NR
NR
42-45 days
NR
NR
1.11 ± 0.35
NR
NR
NR
NR
NR
Thomas et al., 1980
6 mo
NR
NR
1.13 ± 0.91
2.88 ± 2.29
194 ± 151
NR
NR
NR
Levander et al., 1987;
1 mo
NR
NR
1.51 ± 0.11e
NR
NR
NR
9.4 ± 0.5e
84 ± 4e
Moser and Reynolds et al., 1983;
3 mo
NR
NR
1.55 ± 0.08e
NR
NR
NR
12.8 ± 1.8e
84 ± 4e
Reynolds et al., 1984
6 mo
NR
NR
1.51 ± 0.11e
NR
NR
NR
9.6 ± 0.7e
87 ± 4e
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American Indians
Butte et al., 1981
NR
136 ± 115f
4.5 ± 3.8
1.44g
7.96 ± 1.47
169 ± 139
221 ± 114
12.2 ± 5.3
NR
Low-income women
Sneed et al., 1981h
5–7 days
NR
NR
1.52 ± 0.40
7.0 ± 3.1
290 ± 100
NR
NR
NR
43–45 days
NR
NR
1.41 ± 0.56
5.2 ± 1.8
340 ± 200
NR
NR
NR
a From NRC (1989). Details of the studies cited are given in Table 4-4.
b SD = Standard deviation.
c Standard deviation not applicable to RDA.
d NR = Not reported.
e Standard error of the mean.
f Units are IU; 1 µg vitamin D = 40 IU.
g Reported standard deviation is not included because of a suspected error.
h Unsupplemented women.
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CONCLUSIONS
The nutritional status of lactating women in the United States has not been thoroughly or extensively studied; therefore, data are lacking on all aspects of this subject. The lactating subjects who have been studied (mainly Caucasian women with some college education) appear, in general, to be well nourished. Groups of U.S. women who are likely to have poor dietary intakes either tend not to breastfeed or if they do breastfeed, have not been studied extensively.
On average, lactating women who eat to appetite lose weight at the rate of 0.6 to 0.8 kg (1.3 to 1.6 lb) per month in the first 4 to 6 months of lactation, but there is wide variation in the weight loss experience of lactating women (some women gain weight during lactation). Those who continue breastfeeding beyond 4 to 6 months ordinarily continue to lose weight, but at a slower rate than during the first 4 to 6 months. Measurements of subscapular and suprailiac—but not triceps—skinfold thickness decrease during the first 4 to 6 months of lactation.
Until reference standards for nutritional status based on biochemical or anthropometric criteria have been developed for lactating women, there is not a sound basis for using standards derived from nonpregnant, nonlactating women in the routine care of healthy lactating women. If such standards are used in special situations, there is a risk of misclassification. To reduce misclassification, it would be appropriate to consider other factors (such as low socioeconomic status) that might increase the risk of an adverse outcome or factors (such as low weight for height) that might predict the likelihood of a benefit.
RECOMMENDATIONS FOR CLINICAL PRACTICE
Women who plan to breastfeed or who are breastfeeding should be given realistic, health-promoting advice about weight change during lactation (see also Chapters 5 and 9).
In the opinion of the subcommittee, it is not necessary to obtain measurements of skinfold thickness or to conduct laboratory tests as a part of the routine assessment of the nutritional status of lactating women because of the difficulty of obtaining accurate skinfold thickness measurements and the high expense of both types of measurements relative to the likelihood of identifying nutritional problems.
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Representative terms from entire chapter:
nutritional status