JOHNS HOPKINS (US) — People with more chronic environmental exposure to cadmium appear to be nearly 3.5 times more likely to die of liver disease than those with less of the heavy metal in their bodies.
The findings don’t prove that cadmium from such sources as industrial emissions or tobacco smoke directly causes liver disease, but suggest an association that needs more investigation.
Cadmium accumulates in the body over time because of the metal’s long chemical half-life, according to researchers, who report their findings online in the Journal of Gastrointestinal Surgery.
“We already know about the health hazards of heavy metals like lead and mercury, but we don’t know much about what cadmium does to the body,” says study leader Omar Hyder, a postdoctoral fellow in surgery at the Johns Hopkins University School of Medicine.
“In mice, chronic cadmium exposure has been shown to cause liver failure, but we need to understand more about the factors that may cause liver disease in humans and whether we can do anything to prevent it.”
Cadmium is found widely in the environment, with tobacco smoke the most important single source of exposure in the general population. Other environmental sources include fossil fuel combustion and incineration of municipal waste.
For many years, most batteries in the United States were made with cadmium, and it is also found in pigments and plastics.
Long-term exposure is known to cause kidney disease and has been linked to lung cancer. Studies have shown an increase in all-cause mortality and cancer mortality in populations exposed to low levels of cadmium for long periods of time.
For the study researchers analyzed data from 12,732 participants in the National Health and Nutrition Examination Survey, or NHANES III, which includes interviews, physical examinations, blood and urine tests, and ultrasound scans. They looked at cadmium in urine samples, as well as ultrasound tests used to diagnose various liver diseases.
They separated cadmium levels in participants’ urine into four quartiles, finding that those in the highest quartile were nearly 3.5 times as likely to die of liver-related diseases as those in the lower three quartiles.
The diseases included nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, both marked by fatty deposits in the liver that impede its efforts to filter toxins from the bloodstream, aid in digestion, produce hormones, and store energy.
Although occupational exposure to cadmium among factory workers has decreased, environmental exposure continues. If such exposure is ultimately found to cause liver disease, further efforts should be made to reduce it, he says.
The link between cadmium levels and contracting liver disease is disproportionately strong in men. There was not yet enough data in NHANES III, however, to calculate statistically valid death rates by sex.
The sex difference in disease could be due to protective effects of menopause chemistry, which may redistribute stored cadmium from women’s liver and kidneys, where it can do more damage, into bones where it remains more stable, the researchers say.
Source: Johns Hopkins University