In a new study, researchers found that secondhand smoke, which is linked to cancer and other serious illnesses, may also be contributing to soaring rates of chronic liver disease in adults and children.
The findings show that secondhand smoke exposure alters genes and molecular pathways that regulate how the liver processes fats.
These molecular changes may be used as biomarkers to detect the disease at an early stage when it is more treatable.
The research was conducted by a team at the University of Southern California.
In the United States alone, between 30% and 40% of adults are affected by nonalcoholic fatty liver disease (NAFLD).
It is a condition characterized by the accumulation of fat droplets within liver cells in people who drink little or no alcohol.
Among children and adolescents, it is the No. 1 liver disease. Those fat droplets impair normal liver function and can lead to cell rupture, inflammation and ultimately liver cancer.
A number of studies have reported that smoking is an independent risk factor for NAFLD, in addition to obesity and metabolic syndrome.
A weakness of those studies is the number of variables—age, weight, race/ethnicity—that blur the picture.
Animal studies looking at secondhand smoke and liver disease mostly have involved mice that were also fed a high-fat diet making it difficult to tease out the role of secondhand smoke.
In the study, the team compared two groups of healthy mice. Each group was fed a standard diet, but only one was exposed to secondhand smoke.
They found mice exposed to secondhand smoke exhibited more fat deposits in their liver cells, and the fat accumulation continued even after a one-month recovery time in clean air.
These changes have the potential to become irreversible.
The findings also provide a plausible explanation for why children and never-smoking adults are at increased risk of developing NAFLD if they are exposed to secondhand smoke in the household.
From the standpoint of public health, the study has significant implications as it underscores how environmental carcinogens such as secondhand smoke, in addition to cancer-causing effects, may contribute to metabolic liver disease.
The lead author of the study is Stella Tommasi, an assistant professor of research at Keck School of Medicine of USC.
The study is published in the International Journal of Molecular Sciences.
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