Family Size Begets Parent Size

June 1, 2004

The more children a person has, the greater the risk he or she will become obese, according to a new study at Duke Medical Center. The research appears in the January-February issue of the Journal of Women's Health.

Researchers analyzing a large database of middle-aged Americans found that women faced, on average, a 7 percent increase in the risk of obesity per child and men an average 4 percent increase in risk per child. Researchers attribute the weight gain to a busier lifestyle that may include a diet of more fast food and leave less time for exercise.

"As families grow, parents need to be educated about the importance of exercise and a healthy diet," says Lori Bastian, an associate professor of medicine at Duke and a research associate at the Durham VA Medical Center who is a co-author of the paper. "Obesity is a family problem because children follow the lead of their parents. A healthy lifestyle for one is a healthy lifestyle for all," she says.

According to the National Health and Nutrition Survey, 30 percent of all Americans are obese. Obesity is linked to several major health concerns, including diabetes, heart disease, and some cancers. An estimated 300,000 adults die of obesity-related illnesses every year in the U.S.

Women often cite having children as a cause of weight gain and may attribute the gain to physiological changes associated with pregnancy. Several previous studies have indicated a possible relationship between obesity and the number of children a woman has. However, the Duke study is the first to examine the association between parenthood and obesity in both mothers and fathers.

"Increased risk of obesity in both men and women suggests a substantial portion of the effect of obesity related to parenthood has to be social, cultural, or psychological," says Bastian, a physician. "It's difficult to imagine a physiological mechanism through which men could gain weight during pregnancy or after childbirth. Further studies are needed to isolate cause and effect so we can more accurately suggest target groups for obesity prevention and research."

The researchers examined data from the Health and Retirement Study (HRS), a national survey designed to study health, social, and financial issues in middle-aged Americans. The HRS study includes information on more than 12,600 Americans, collected from 1993 to 2000. Most respondents were age fifty-one to sixty in 1992. The study is a cooperative agreement between the In-stitute for Social Research at the University of Michigan and the National Institute on Aging. For the Duke analysis, the researchers used data only from a baseline survey completed in 1992. Only married respondents and spouses between the ages of forty and seventy with children were included in the analysis, which comprised a total of 9,046 men and women (4,523 couples). Single or divorced individuals with children were excluded. The number of children reported by the couples ranged from one to nineteen, and included both biological and adopted children. Of the sample, 79 percent were white, 12.5 percent were African American, and 8.5 percent were Hispanic.

Because the researchers focused their analysis exclusively on the connection between number of children and obesity, they controlled for age, household income, race and ethnicity, work status, physical activity, and tobacco and alcohol use. "After adjusting for all these factors, the number of children played a statistically significant role in the obesity of both men and women," says Truls Ostbye, senior author on the paper and professor of community and family medicine at Duke.

Ostbye says that, while the increased risk for obesity in women was 7 percent for each additional child and only 4 percent for men, the difference between these two figures was not statistically significant. "Obesity associated with number of children is not just a problem linked to physiological changes in women during pregnancy," he says. "There are social, cultural, or psychological mechanisms that bring about this weight gain, and this is illustrated by our results that showed men were also at a greater risk of obesity."