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Duration of Poverty and Child Health in the Quebec Longitudinal Study of Child Development: Longitudinal Analysis of a Birth Cohort

Department of Social and Preventive Medicine and Interdisciplinary Health Research Group, University of Montreal, Montreal, Quebec, Canada

	ABSTRACT

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OBJECTIVES. The objective of this study was to examine the relationship between duration of poverty and the health of preschool children in the Quebec Longitudinal Study of Child Development birth cohort.

METHODS. Data from the Quebec Longitudinal Study of Child Development for 1950 children who were followed annually up to age 3 years were analyzed. Poverty was defined as having an income below the low-income cutoff from Statistics Canada. Five health indicators were examined: asthma attacks, infections, growth delay, a cumulative health-problems index, and maternal perception of the child's health. The association between duration of poverty and child health was explored with logistic regression modeling controlling for child and mother characteristics, including the mother's level of education, social support, and physical violence.

RESULTS. In this birth cohort, 13.7% (268) 3-year-old children from the Quebec Longitudinal Study of Child Development experienced intermittent poverty since birth (1–2 episodes), and another 14.4% (280) experienced chronic poverty (3–4 episodes). Children from families with chronic poverty had more frequent asthma attacks and had a higher cumulative health-problems index score, whereas children with intermittent poverty were more often perceived to be in less than very good health by their mothers. These associations remained statistically significant when controlling for child and mother characteristics. No association was observed between duration of poverty and infections or growth delay.

CONCLUSIONS. Chronic poverty affects a large number of children and has negative consequences for preschool children's health, although universal health care is available. The effects of chronic poverty may vary according to different health indicators and the age of the child.

Key Words: child health • poverty • socioeconomic status • asthma attacks • maternal perception of child's health

Abbreviations: SES—socioeconomic status • QLSCD—Quebec Longitudinal Study of Child Development • CHPI—cumulative health-problems index • LICO—low-income cutoff • OR—odds ratio • CI—confidence interval

The relationship between socioeconomic status (SES) and child health has been observed in industrialized countries.^1–6 These associations also are present when poverty is defined as a lack of material resources or low income.^7,8 Poverty is not a static condition, and there are many entries in and exits from poverty in any 1 year.⁹ However, poverty dynamics are not always taken into account when the associations with children health are studied, because most studies in this area rely on cross-sectional measures of poverty.¹⁰ Short duration of poverty does not entail the same consequences for a child's health as does longer duration of poverty. Chronic poverty seems to be especially harmful for young children because it is associated with a higher risk for mortality and for morbidity.^5,11–13 Moreover, poverty during early childhood not only affects child health but also jeopardizes future adult health. Numerous adult chronic health problems, such as cardiovascular diseases, originate during pregnancy and the first years of life when the child's family is poor.^14–17 However, few longitudinal studies have examined the health of preschool children in relation to their family's financial difficulties.⁵

Population studies about child health most often analyze chronic health problems,^7,18–20 asthma,^13,21,22 infections, and growth delay.^7,23–26 Most of these studies are cross-sectional, analyze only 1 or 2 health indicators, and include heterogeneous samples of children who are younger than 18 years. Few studies have controlled for both maternal and child characteristics that could attenuate the relationship between chronic poverty and child health. Last, most of these studies pertain to children who live in the United States. Universal access to health care and various social programs that are specific to Quebec, such as the low-cost child care system, could buffer the effects of poverty on health among poor children. In this article, we examine the relationships between duration of exposure to poverty since birth and the health of 3-year-old children focusing on 5 health indicators (asthma attacks, infections, growth delay, a cumulative health-problems index [CHPI], and maternal perception of the child's health) while controlling for the child's and the mother's health and social characteristics.

	METHODS

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Data came from the first 4 cycles of the Quebec Longitudinal Study of Child Development (QLSCD), which was coordinated by the Direction Santé Québec of the Institut de la statistique du Québec. A birth cohort of 2120 children was followed up annually since 1998. The sample was representative of singleton live births registered in the Quebec live births registry in 1997–1998 with the exception of those on the Cri and Inuit territories, on Indian reservations, or in the Northern region of Quebec (2.1% of live births).²⁷ Infants who were born before 24 or after 42 gestational weeks (0.1%) and those with unknown gestational age (1.3%) were excluded. At 41 months, the participation rate was 92% (n = 1950).

Data on health conditions at birth were taken from hospital files. After informed consent was given, structured interviews were conducted at home by trained interviewers at 5, 17, 29, and 41 months with the person most knowledgeable about the child (the mother in 98% of cases). At 29 and 41 months, the interviewers measured the child's height with a standardized procedure.

Five health indicators were used to examine the health of the child at 41 months: reports by the mother of the occurrence in the previous 12 months of an asthma attack, maternal report of the occurrence of an infection (respiratory, otitis, gastroenteritis, other) in the previous 3 months, perception of the child's health by the mother, growth delay, and the CHPI. Growth delay was defined as a z score of the child's height under the 10th percentile of the Centers for Disease Control and Prevention's growth curves.²⁸ The CHPI identifies children who accumulate 2 or more of the following health problems: asthma attacks, infections, and growth delay.

Poverty was defined in terms of insufficient household income, that is, having an income during the past 12 months below the Canadian low-income cutoff (LICO) as estimated by Statistics Canada.²⁹ A family is said to be under the LICO when they attribute 20% more than the average Canadian family to food, shelter, and clothing. There are different cutoffs according to the number of people in a household and whether the household is located in a rural area or a small or large urban area. Duration of poverty was categorized as never poor, intermittently poor (1–2 episodes of being under the LICO out of the 4 follow-up periods), or chronically poor (3–4 episodes).

The possible confounding variables included child characteristics (gender, age, birth order, duration of breastfeeding, and birth conditions [preterm birth, small for gestational age, and congenital malformation]), mother characteristics (age at birth of the child, education, immigration status, height, and social support), and child environment (smoking in the house, family type, child care, and exposure to physical violence). Social support was assessed with a validated shortened version of the Social Provisions Scale,³⁰ which originated from the National Longitudinal Study of Children and Youth.^27,31,32 In particular, factor analysis of the National Longitudinal Study of Children and Youth data showed that 3 items could adequately ascertain social support: extent of mother's access to people who make her feel secure and happy, extent of mother's access to people in whom she can confide, and extent of mother's access to people who can provide material aid when necessary. Summation of values on the 3 items was standardized to create a score that ranged from 0 to 10, with higher values indicating greater support. Physical violence was established with 1 question that was addressed to the mother at 41 months, which inquired about whether she had been beaten, pushed, or hurt since the birth of the child. This question was adapted from the validated Abuse Assessment Screen.³³

In analysis, first we examined univariate associations between duration of poverty and each health indicator. Second, the possible confounding role of each risk factor was examined for each health outcome by fitting a logistic model. A risk factor was considered a confounder in the association of poverty with child's health when the value of the coefficient of poverty changed by at least 10% after inclusion of the potential confounder.³⁴ Third, a final model that included duration of poverty and all confounders was built. We also tested the potential interacting and mediating roles of social support in the poverty–health associations. All of the analyses were performed with SPSS 11.00 (SPSS, Chicago, IL). Missing cases were excluded listwise. This study was approved by the University of Montreal Faculty of Medicine Human Research Ethics Committee.

	RESULTS

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Results show that 13.7% (268) of 3-year-old Quebec children in the QLSCD study had experienced 1 or 2 episodes of poverty since their birth, and 14.4% (280) had experienced chronic poverty with 3 or 4 episodes of poverty since their birth, so 28.1% (548) of them had spent at least 1 year in poverty before the age of 3 years (Table 1). As shown in Table 2, health problems are more frequent for children who have experienced poverty and more so for chronic poverty with the possible exception of infections. Most health risk factors show differences between children whose families have never been poor and those who have experienced 1 or more episodes of poverty (Table 3). Poor mothers have more children, and they breastfeed less often or, if so, during a shorter period than mothers with sufficient income. They are more likely to be young, have limited education, be heading single-parent families, be non-European immigrants, be of a shorter height, and be smokers. They receive less social support from their network and more often report having been subjected to physical violence.

View this table: [in this window] [in a new window]   TABLE 1 Distribution of 3-Year-Old Children According to Duration of Exposure to Poverty

View this table: [in this window] [in a new window]   TABLE 2 Distribution of Health Problems That Occurred Between the Ages of 2 and 3 Years According to Number of Episodes of Poverty Since Birth

View this table: [in this window] [in a new window]   TABLE 4 Nonadjusted and Adjusted ORs for the Association Between Duration of Exposure to Poverty and the Occurrence of at Least 1 Asthma Attack, a Cumulative CHPI >1, and Maternal Perception of Child's Health as Less Than Very Good, Between the Ages of 2 and 3 Years

View this table: [in this window] [in a new window]   TABLE 5 Nonadjusted and Adjusted ORs for the Association Between Duration of Exposure to Poverty and the Occurrence of Infections and Growth Retardation Between the Ages of 2 and 3 Years

In the asthma model, gender and birth order of the child remained significant predictors. In the CHPI model, the child's gender and age, being born small for gestational age, the mother's height, and the use of a child care center contributed uniquely to a poorer health outcome. In the analysis of maternal perception of the child's health, low social support increased the odds of being perceived as being in less than very good health by the mother. Use of a child care center, being a non-European immigrant, and receiving low social support are linked with infections. Last, being born small for gestational age and short maternal height are predictors of growth delay.

	DISCUSSION

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The objective of this study was to examine the relationship between duration of exposure to poverty since birth and preschool children's health among children in the QLSCD using 5 different health indicators. Results show that many children live in families who experienced at least 1 episode of poverty during their first years of life. More than one quarter (28.1%) of families lived for at least 1 year with insufficient income between the time when the child was born until the age of 3 years. Moreover, for 14.4% of them, this situation was repeated 3 to 4 times. This level of poverty is similar to what is observed in the rest of Canada and in other industrialized countries such as the United States and Great Britain, where children are most often afflicted by poverty among all age groups in the population.^4,6,35,36 However, some European countries, using diverse fiscal measures, are successful in reducing the number of children who are exposed to poverty. According to a United Nations Children's Fund report based on Organisation for Economic Co-operation and Development data,³⁷ after taxes and social benefits, 14.9% of Canadian children were living in a poor family in 2000, 21.9% of children were poor in the United States, but no more than 2.8% to 4.2% of children were living in poverty in Scandinavian countries.

Chronic poverty has negative impacts on the health of preschool children who have more frequent asthma attacks and a greater number of health problems than children from nonpoor families. These results confirm those that link health with chronic poverty.^{21,22,38–41} Some authors hypothesized that the more frequent asthma attacks among poor children would be the result of limited access to health care, yet here we report a similar finding for children who live in a society with universal access to health care and a low-cost child care system. Similar results were observed in other parts of Canada^13,42 as well as in other countries where health care is financially accessible.⁷ In this cohort, we observed that poor mothers consulted health professionals for their children as often as did nonpoor mothers, yet it is possible that mothers in poor families have more difficulty complying with the daily treatment for their child's asthma.⁴³ Unfavorable housing conditions, living in a more polluted environment, and more frequent smoking by their parents can play a role in eliciting more frequent asthma attacks among chronically poor children.^44–46 Moreover, stress that results from living in conditions of poverty might play a major role in the links between low SES and asthma in children.^47,48

Chronic poverty is also associated with a higher score on the CHPI, which means that poor children are more likely to have >1 of the health problems included in the index. Similar results were observed in other studies that used a similar index.⁴¹ This higher number of health problems among poor children might reflect a higher general vulnerability that could result from chronic stress. Stress that results from these difficult living conditions and the biological stress process that ensues can affect the body's capacity to prevent onset of disease processes.^49–53

In this analysis, maternal perception of children's health is worse only for children who experienced transient episodes of poverty. In an earlier analysis, we demonstrated that maternal perception of child's health is a valid indicator of health at 17 months because it was associated with the presence of health problems in the child after controlling for mother's demographic and socioeconomic characteristics.⁵⁴ That maternal perception of child health is not worse for children who are chronically poor compared with children who were never poor might result from a lack of statistical power. It also could be attributable to the selected attrition of mothers with a low level of education, mothers who head single-parent families, and non-European immigrant mothers who also are chronically poor mothers.

In this analysis, infections were not associated with chronic poverty at this age. In a previous analysis of these children when they were aged 2 years, a clear link between chronic poverty and infections was reported.¹¹ At 3 years, more children regularly attend a child care center, a widely known source of infections.⁵⁵ However, children from families who did not experience poverty are more often cared for in a child care center than poor children, who are more often cared for at home.⁵⁶ Low social support of the mother, use of a child care center, and being an immigrant were risk factors for infections.

No relationship between chronic poverty and growth delay of children was observed in this study. An association often has been reported between family SES and children's height even in industrialized countries.^7,23–26 Our observation of the absence of an association could be the result of a secular tendency toward greater height, which is still ongoing in certain populations.⁵⁷ In the Quebec population, children often are observed to be taller than their parents. This type of phenomenon is thought to be especially prevalent among poor individuals because they are of a shorter stature to begin with.⁵⁷ As a result, any association between poverty and growth retardation could be confounded by the intergenerational secular trend in height. It also is possible that the poverty measure (below the LICO) that was used in this study is not specific enough, because a previous set of analyses on the same cohort of QLSCD children revealed a relationship between poverty as measured with a scale of a lack of money for basic needs and a growth delay when the children were 2 and 5 years of age.⁵⁸ That is, a measure of poverty on the basis of annual household income (as used here) does not provide information on other possible financial resources from members of the extended family or from personal savings. Moreover, with such a measure of poverty, those who are just above the poverty threshold are classified as having sufficient income even though they experience hardships as a result of limited financial resources, which is not the case of those who have a much higher income. This lack of specificity in the poverty measurement also could explain the lack of association between chronic poverty and some of our other health indicators, such as infections.

Our study has other limitations. Although the child's height was measured by the interviewer and the birth conditions were extracted from hospital records, other information about the child's health are reported by the mother.⁵⁹ We observed in this cohort that maternal perception of her child's health was linked with the presence of health problems.⁵⁴ It also is possible that effect sizes for poverty in our modeling are underestimated as a result of overadjustment, because many of the variables that we used as confounders are actually conceptually related to our exposure of interest.

There also are strengths in our study. This birth cohort of children was followed up annually since they were 5 months of age, and the participation rate is high. Data are collected at home by experienced interviewers using questions and instruments that have been used extensively in Canadian and American surveys. Hospital birth records were used to code for birth conditions such as preterm birth, being small for gestational age, and congenital malformations that are known risk factors for health problems during childhood, especially among poor children.^41,60,61

	CONCLUSIONS

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Despite governmental promises to end child poverty, chronic poverty affects a large proportion of families with young children in Quebec. Chronic poverty has important negative consequences for young children's health beyond being born preterm or small for gestational age and beyond low maternal education. The strength of the association between chronic poverty and health may vary according to different health indicators because not all health problems of preschool children were linked with chronic poverty. Effects of chronic poverty also may vary with the age of the child. Although some health problems are more frequent among young poor children, for other problems, a relationship might emerge later.

It is difficult to generalize the results of this investigation to children from the United States, where access to health care and social policies are different. Moreover, the population studied here is not as heterogeneous as the population in the United States. Remaining disparities in child health despite a universal health care system and a low-cost child care system suggests that unfavorable living conditions and chronic stress that emanates from chronic poverty have a negative impact on child health; therefore, eliminating child poverty should be the target for change.

	ACKNOWLEDGMENTS

 
This study was funded by Canadian Institute of Health Research grant 00309MOP-123079. Data were collected by the Insitut de la Statistique du Québec, Direction Santé Québec.

	FOOTNOTES

 
Accepted Nov 1, 2006.

Address correspondence to Louise Séguin, MD, MPH, Department of Social and Preventive Medicine, University of Montreal, C.P. 6128 succ Centre-Ville, Montreal, Quebec, Canada H3C 3J7. E-mail: louise.seguin{at}umontreal.ca

The authors have indicated they have no financial relationships relevant to this article to disclose.

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