Socioeconomic status alone might not be as reliable a predictor of body mass index (BMI) in U.S. residents as previously thought, according to a new study.
The influence of gender, ethnicity and birthplace are also worth considering when screening for obesity risk and other BMI-related health issues, argue study authors led by Emma Sánchez-Vaznaugh, a postdoctoral fellow at the University of California San Francisco's Center on Social Disparities in Health.
The researchers used data from the 2001 California Health Interview Survey - conducted in seven languages and dialects - which comprised 37,150 people between the ages of 25 and 64. Of these, 56 percent were whites, 6 percent were black, 13 percent were Asians and 25 percent were Hispanic.
The connection between SES and BMI "differed markedly" by ethnicity and varied within ethnicity, according to the researchers. The widest disparity occurred among Asian subgroups.
"Although Asians as a whole may appear healthier than whites, this is not necessarily the case when we separate Asians according to birthplace and gender," Sánchez-Vaznaugh said. The study appears online in the American Journal of Epidemiology .
While many accept that lower socioeconomic status relates to higher BMI, particularly among women, the researchers questioned whether this is the case and if the correlation holds true within gender and ethnic groups. They also looked at the significance of being born within or outside of the United States.
"U.S.-born Asians/Pacific Islander men with low SES - income and education - had among the highest average BMI of all groups combined," Sánchez-Vaznaugh said. In this group, the average BMI was about 31.
"By contrast, foreign-born Asian women had the lowest BMI irrespective of income and education levels," she said. Average BMI was about 20 for these women and slightly more than 25 for foreign-born Asian men.
Most experts consider a person with a BMI of 30 or above to be obese.
"When treating people who are vulnerable to obesity, clinicians should keep in mind that this research identifies societal factors - not just individual choices - as important contributors to BMI," said Sánchez-Vaznaugh, who is also an assistant professor for San Francisco State University's Department of Health Education.
Sánchez-Vaznaugh noted study limitations: for instance, they could not substantiate participants' self-reported height and weight. In addition, because data collection did not occur over time, researchers could not show a causal relationship between SES and BMI.
Her research was supported by the W.K. Kellogg Foundation's Health Policy Research Fellowship Program, which is directed by a National Program Office at the Center for Advancing Health.
The American Journal of Epidemiology is published by Oxford Journals, a division of Oxford University Press, on behalf of The Johns Hopkins Bloomberg School of Public Health. Please acknowledge the journal as a source in any articles. For more information, visit http://aje.oxfordjournals.org/ or contact Helen Ison, Communications Executive, Oxford Journals at [email protected] or +44 (0)1865 353043.
Sánchez-Vaznaugh EV, et al. Do socioeconomic gradients in BMI vary by race-ethnicity, gender and birthplace? Am J Epidemiol online, 2009. doi:10.1093/aje/kwp027