THE FREQUENCY OF BREAST FEEDING IN A REPRESENTATIVE SAMPLE OF

WOMEN IN A METROPOLITAN AREA DANIEL HORN, PH.D., AND ERWIN S. SOLOMON, M.A.

T HAS OFTEN been suggested that failure to I breast feed babies is correlated with the later development of breast cancer in women. The evidence on the subject is equivocal. One of the difficulties in any retrospective study of possible etiological factors in the epidemiol- ogy of cancer is knowing how to select a con- trol group, that is, on what factors to control.

In the course of a recent study of the effec- tiveness of a mass open showing of the Ameri- can Cancer Society’s film Breast Self-Exami- nation, we interviewed approximately 2,000 women who were representative of the adult female population of the metropolitan area of Detroit, Mich. Feeling that interest and con- cern in the subject matter of the movie and, hence, attendance might be related to breast- feeding practices, we included the following question in the interview: “Did you breast feed any of your children?”

As it turned out, our idea was wrong, and we found no significant correlation with at- tendance at the movie that was not already accounted for by other factors. We have been unable to find in the literature any represent- ative United States population data on breast feeding and demographic factors associated with it. These findings are presented in the hope that they will be of value in the design- ing of epidemiological studies to determine the rela tionship of breast feeding to breast cancer. Findings are presented for 4 demo- graphic factors: age, race, socioeconomic status, and fertility.

Age. This is age as of 1955. It may be that year of birth is more significant than age, since the cultural climate during the child- bearing years may well be of more importance than chronological age per se.

Race. This is limited to white and Negro. Eighteen per cent of the respondents were Negro.

From the Medical Affairs Department, American

Received for publication April 28, 1958. Cancer Society, Inc., New York, N.Y.

TABLE 1 BREAST FEEDING BY SELECTED

DEMOGRAPHIC FACTORS ~~~~~~~ ~ ~

Percentage of breast feeders

Factor women* All women Fertile women No.

Ace, P. 21-29 382 30-44 763 45-59 51 1 60 or more 272 Race Negro 35 1

Socioeconomic slatus Low low 250 Upper low 390 Low middle 464 Upper middle 287 Low high 329

Fertility, no. children 0 230 1 320

White 1,574

Upper high 220

2 3 4 5

. ~ .

508 380 1M) 120

6 or mnre 174

45.8 53.8 55.3 62.6 65.0 82.0 66.9 87.1

61 .O 79.9 56.7 66.6

66.8 82.3 63.3 76.0 55.8 64.4 50.9 59.8 52.6 63.8 56.4 70.9

... . . . 53.4 53.4 63.4 63.4 71.3 71.3 80.0 eo.0 84.2 84.2 88.5 88.5

*The number of women in the various groups differs from group to group because of incomplete data.

Socioeconomic Status. This is based on an index combining educational level, family in- come, and occupation of the head of the household. The index was then subdivided into 6 levels, each representing roughly one- sixth of the population. In order to increase the numbers in the subgroups, however, these were regrouped into the high, middle, and low thirds of the population.

Fertility. This is reported in terms of num- ber of children. A distinct limitation of the data lies in the fact that we asked if the respondent had ever breast fed a child. Ob- viously, the more children, the greater the opportunity to breast feed at least 1 child. Since congestion as a result of not breast feed- ing has been proposed as a possible mecha- nism of breast cancer, a more pertinent ques- tion might be whether or not the mother had ever given birth to a child who had not been

191

192 CANCER January-February 1959 VOl. 12

TABLE 2 PERCENTAGE OF WOMEN BY SOCIO- ECONOMIC STATUS, AGE, RACE, AND FERTILITY WHO HAVE EVER BREAST

FED THEIR CHILDREN Percentage breast feeders by race &

no. children*

1-3 children 4 or more children

Age, yr. Negro White Negro White Low economic status 21-29 68.4 45.2 81.8 (66.7) 30-44 77.4 58.2 80.0 78.9 45-59 82.6 80.3 89.5 87.9 60ormore 84.6 79.2 100.0 91.2 Middle economic status 21-29 66.7 43.2 75.0 61.5 30-44 55.0 53.5 92.3 78.2 45-59 (80.0) 72.9 (100.0) 90.3 60ormore (100.0) 87.9 ... 88.2 High economic status 21-29 (83.3) 54.1 (83.3) 30-44 (85.7) 54.6 (100:O) 73.5 45-59 (80.0) 79.2 (100.0) 90.0 60 or more ... 73.7 ... (100.0)

*Percentages in parentheses are based on fewer than 10 women.

breast fed, or who had been weaned early and abruptly. This would include stillbirths and early infant deaths, which are usually not re- ported under “number of children.”

More than two-thirds (68.9%) of the women who had ever had children had breast fed at least 1 of their children. This represents 57.9% of all adult women. All 4 demographic factors are related to breast feeding. Table 1 shows the number of women in each classifi- cation and the percentage of breast feeders among (1) all of the women interviewed and (2) fertile women.

The following relationships to breast feed- ing were established: . Age. Among fertile women, the percentage who breast feed their children is 53.8% in the youngest age group (21 to 29) and goes up steadily with increasing age to 87.1% among women 60 years of age and over.

Race. Negro women have a higher percent- age who breast feed their children (79.9%) than do white women (66.6%).

Socioeconomic Status. The relationship be- tween socioeconomic status and breast feeding is U shaped. The highest proportion of

mothers who breast feed their children are found in the lowest economic groups in the population (82.3% and 76.0%) and the next highest is found in the highest economic group in the population (70.9%). The lowest proportion is found in the upper middle

Fertility. There are more breast feeders among women with many children than among women with few children. The per- centage rises from 53.4% for mothers who have 1 child to 88.5% for mothers of 6 or more children. As has already been pointed out, the data are limited in that the women were not asked how many of their children they had breast fed, or whether they had any children whom they had not breast fed. Nat- urally, the more children, the greater the number of opportunities to breast feed at least 1 child.

Obviously, these 4 factors are themselves interrelated, yet the relationship to breast feeding holds for each factor even when the others are controlled. Table 2 shows the per- centage of breast feeders for each combination of the 4 factors. In order to obtain a reason- able number of cases in each cell, it was nec- essary to combine some of the categories for fertility and socioeconomic status. Even with these combinations, some of the subclass pop- ulations are small, and percentages based on fewer than 10 women appear in parentheses. Despite the small number of women in some of the subclasses, the trend for each factor is clear, even when the other 3 factors are con- trolled.

The limitations of the data imposed by the restricted nature of the questioning have al- ready been mentioned. The findings point to the importance of demographic factors in the determination of whether or not a mother breast feeds her child. We obtained no infor- mation on religious affiliations, on nativity, or on familial country of origin of the respond- ents. These could easily be significant factors in addition to the ones represented here. The importance of controlling such factors in any epidemiological study of breast feeding in relation to breast cancer cannot be over- emphasized.

group (59.8%).