Environmental pollutants trapped in fat cells could be released back into circulation when people shed a lot of weight, researchers said.
According to data collected from among 1,099 adult participants age ≥40 in the CDC's National Health and Nutrition Examination Survey (NHANES), serum concentrations of six persistent organic pollutants were significantly correlated with weight change, according to Duk-Hee Lee, MD, PhD, of Kyungpook National University in Daegu, Korea, and colleagues.
Adjusted correlation coefficients for 10-year weight changes ranged from -0.16 to -0.23 for the six pollutants, with slightly smaller coefficients found for one-year weight changes, the researchers reported online in the International Journal of Obesity.
Correlations between serum pollutant levels and five categories of weight-loss -- stable weight, moderate increase or decrease, and large increase or decrease -- were significant (P<0.01) for all but one of the six pollutants.
Compared with participants who reported large weight gains over the previous decade, those claiming large losses had serum levels of the six pollutants that were about 50% higher, Lee and colleagues found.
Although the cross-sectional study design could not establish that weight loss itself led to the higher concentrations of circulating organic pollutants, the findings were consistent with such a mechanism, the researchers suggested.
"As persistent organic pollutants mainly bioaccumulate in adipose tissue, weight change can affect serum concentrations," they explained. Lee and colleagues also noted that some small longitudinal studies have already found evidence that these chemicals are released from fat tissue after short-term weight losses.
The researchers suggested that such releases may account for some adverse outcomes seen in people undergoing large weight losses, including increased rates of cardiovascular disease, dementia, and death.
"These puzzling findings on weight change from observational studies have been dismissed simply as bias due to no biological plausibility," Lee and colleagues wrote, suggesting that these effects are mixed with the benefits of weight loss in previously obese individuals.
"Pathogenesis of some health outcomes may be more affected by the change of adipose tissue mass, while pathogenesis of other health outcomes may be more affected by the change of serum concentrations of persistent organic pollutants," they argued.
Their study involved data from 1999 to 2002 NHANES series, in which serum levels of 49 organic pollutants that are not metabolized in vivo were measured in some participants.
Since most of these pollutants turned out to be undetectable in many samples, Lee and colleagues focused on the seven with the highest detection rates in participants who were at least 40 years old. The study group was comprised of 49% men and over half were white.
These chemicals included trans-nonachlor, p,p'-DDE, beta-hexachlorocyclohexane, PCB169, PCB180, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, and 1,2,3,4,6,7,8-heptachlorodibenzofuran (HpCDF).
Participants in NHANES also reported their weight at year one and 10 years earlier, allowing for weight change to be estimated over time. Lee and colleagues stratified these estimates into five categories for each period: stable weight, moderate increase or decrease, and large increase or decrease.
For one-year change, stable weight was a gain or loss of less than 1 kg (2.2 lb). Moderate change was 1 to 5 kg (11 lb) and large change was more than 5 kg. The 10-year weight-change categories were double these ranges (that is, large change was more than 10 kg or 22 lbs) and moderate change was 2 to 10 kg (4.4 to 22 lbs).
The correlations between the weight-loss categories and the serum pollutant levels were significant (P<0.01) for all but HpCDF -- for which the correlation coefficient was -0.05 (P=0.12).
Lee and colleagues acknowledged that the study design allowed for potential confounding and error, insofar as each participant had only one serum measurement of pollutant levels and reported their own previous weights.
Also, it remained possible that factors other than weight loss, which were not analyzed in the current study, were also associated with the serum pollutant levels. Thus, they recommended more studies of the potential relationship.
However, pending the outcome of such future studies, "researchers and clinicians need to consider lipophilic xenobiotics such as persistent organic pollutants that bioaccumulate in adipose tissue as well as obesity itself when they study or manage obesity issues because such xenobiotics may work against what we generally expect from weight loss or gain," Lee and colleagues concluded.
No external funding for the study was reported.
The authors declared they had no conflicts of interest.
Zalman S. Agus, MD Emeritus Professor
University of Pennsylvania School of Medicine and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner