Association of maternal smoking with overweight at age 3 y in American Indian children

Nutrition Research Newsletter, Sept, 2005 by A. Adams, H. Harvey, R. Prince

The prevalence of childhood obesity in 2 year-olds to 5 year-olds has increased 34% in the past 10 y, and the highest rates appear in minority populations. The most recent data indicated that 14.3% of children aged 2 y to 5 y were overweight, and an additional 15.4% were at risk of overweight. It is estimated that overweight children are 1.4 to 4 times as likely to become overweight adults as are normal-weight children, and this results in a public health issue &great significance.

American Indian communities have the highest rates of childhood obesity of any ethnic group in the United States. American Indian adult mortality due to cardiovascular disease is highest and diabetes is second highest among American Indians living in the Bemidji Indian Health Service Area comprising the states of Minnesota, Wisconsin, and Michigan. However, little research has been conducted on the prevalence or predictors of obesity among American Indians in this area. Because of the inherent difficulty of treating overweight and obesity and because of the link of overweight and obesity to adult disease, it is imperative that preventive measures are employed. This study used linked data from five years of Wisconsin Pediatric Nutrition Surveillance System (PedNSS), Pregnancy Nutrition Surveillance System (PNSS), and birth records to identify predictors of overweight in American Indian children at age 3 y. Maternal and child predictors included were birth weight, breastfeeding, maternal prepregnancy BMI (in kg/m2), family income, maternal weight change during pregnancy, smoking, and education. This information will help in the design and evaluation of community-based obesity prevention programs in American Indian tribes in Wisconsin.

The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) operated by the Food and Nutrition Service of the US Department of Agriculture collects information on maternal, prenatal and postnatal characteristics and demographics, and also performs child growth and nutrition measurements from birth to age 5 y. These data, along with Head Start and maternal and child health data, are reported to the Centers for Disease Control and Prevention (CDC) by the states and stored as two data sets, the PNSS and the PedNSS. In Wisconsin, only WIC data are reported to the CDC. These data sets offer an opportunity to look at familial and environmental determinants of overweight in children from lower socioeconomic environments. WIC serves 48% of American Indian infants and children and 65% of American Indian women.

The PedNSS and PNSS data sets were obtained from the CDC for all Wisconsin records for the years 1997 through 2001. Birth records for all American Indian births from 1997 through 2001 were obtained from the Bureau of Health Information, Division of Health Care Financing, Wisconsin Department of Health and Family Services. These records included demographic and birth data for both the mother and the child. An employee of the Wisconsin Department of Health and Family Services matched mothers' PNSS and children's PedNSS records to birth records. Researchers obtained 1649 PNSS matemal records. A total of 6769 American Indian birth records were obtained, of which 3439 (51%) were matched to PNSS and PedNSS records. The 3439 mother-child pairs were further decreased to 252 unique pairs when children born at <36 wk gestation (n = 424) and children for whom maternal smoking (n = 267), birth (n = 321), or 36-month weight and height (n = 2797) information was missing were excluded.

This retrospective analysis of linked PedNSS, PNSS, and birth record data for Wisconsin American Indians documented high rates of overweight risk status and overweight at age 3 y. Maternal smoking was a significant predictor of overweight risk status and overweight. Children of mothers who smoked during pregnancy showed significantly greater rates of weight gain than did children of nonsmokers, which resulted in significantly greater increases in WFL z score between birth and age 3 y.

In this study population, 22.2% of children were at risk of overweight and 18.7% were overweight. These rates are higher than those of overweight reported nationally for 3-year-old American Indian WIC participants--14.4%. Moreover, 18.7% of the children in the sample in the current study were LGA, whereas national American Indian and Wisconsin all-race proportions are 11.3% and 8.7%, respectively. This high rate of LGA is especially troubling, given the correlation between birth weight and later BMI seen in this study and in others. Rates of breastfeeding were comparable to reported all-race national and state rates of 52.5% and 55.0%, respectively, but were slightly below national rates of 59% for American Indians participating in WIC. In this population, children of mothers who smoked at the initial WlC visit were almost twice as likely as children of nonsmokers to have a BMI e"85th percentile at age 36 months.

This is the first study to show a relation between smoking in pregnancy and later overweight in American Indian children. Given the limitations and potential biases inherent in retrospective analysis, prospective cohort studies would be an ideal next step in evaluating the suggested relation between smoking and overweight. These results have important implications for healthcare and point to the need for targeted interventions to reduce smoking in pregnant women and women of childbearing age. A similar message should be communicated at the initial WIC visit and at subsequent WIC visits throughout a pregnancy.