Newswise — A new analysis of government data on more than 6,000 American women indicates that deposition of mercury within the human population due to chronic mercury exposure is increasing over time. This study also found that deposition of mercury increases with age. In addition, this study demonstrates significant associations between chronic mercury exposure and both the immune and endocrine systems that may explain a mechanism for the association with neurodegenerative and neurodevelopmental disease. Specifically, this study discovered that levels of the pituitary hormone, lutropin (luteinizing hormone) are significantly associated with chronic mercury exposure.
“My study found compelling evidence that inorganic mercury deposition within the human body is a cumulative process, increasing with age and overall in the population over time,” said study author Dan R. Laks, M.S., a neuroscience researcher at the David Geffen School of Medicine at UCLA. “My findings also suggest a rise in risks for disease associated with mercury over time.”
The study is published online in Biometals, an international peer review journal on the role of metal ions in biology, biochemistry and medicine, and will appear in a future print edition of the journal. One of the journal’s peer reviewers commented that, “This is a highly important contribution as there are very few publications that have enough subjects to evaluate accurately the effects of increased body levels of mercury on biomedical parameters in humans.”
Laks conducted computer analyses of data from the Centers for Disease Control and Prevention’s (CDC) National Health and Nutrition Examination Survey (NHANES). He examined data over time on blood inorganic mercury levels of 6,168 women, ages 18-49, in NHANES data sets from 1999-2000, 2001-2002, 2003-2004 and 2005-2006 (between 1,455 and 1,622 women were in each two-year matched group).
Laks found that inorganic mercury was detected in the blood of 30 percent of women studied in 2005-2006, up from two percent of women in the 1999-2000 study. The overall population average of blood inorganic mercury concentration also increased significantly from 1999-2006. In a separate statistical analysis, he found that older women had more inorganic mercury in their blood than younger women. His analysis also revealed significant associations of both blood inorganic mercury detection and average concentration with biomarkers for the main organs and systems which mercury targets: the liver, the immune system, and the pituitary gland.
NHANES, considered the “gold standard” in assessing the health status and health risks to a representative group of Americans, is unique in that it combines interviews and physical examinations. NHANES data are also designed and survey weighted so that results can be generalizable to the nation’s population.
Numerous studies have associated chronic mercury exposure with elevated risks for autism, mental impairment and neurodegenerative disorders such as Alzheimer’s disease. An earlier analysis of NHANES data by U.S. Environmental Protection Administration (EPA) researchers estimated that, as a result of chronic mercury exposure, between 300,000 and 600,000 American children were born with elevated risks of neurodevelopmental disorders between 1999 and 2000.
Among the sources of environmental exposure to mercury, a potent neurotoxin, are contaminated fish, coal-burning power plants, dental fillings and vaccines that include the preservative thimerosal. Mercury has elemental, organic and inorganic forms, which account for various sources of exposure. Mercury found in fish, for example, is organic. Animal studies have shown that in chronic exposure to organic mercury, the metal converts to its inorganic form, which deposits in the brain. These deposits can last for years. For this reason, inorganic mercury may be considered the best measure of chronic mercury exposure.
A consensus of leading international scientists declared in 2006 that both the rate of mercury emissions from coal-burning power plants and the rate of mercury deposition from the atmosphere are increasing over time. A 2007 population-based longitudinal study found that some neurodevelopmental disorders associated with mercury exposure may also be rising over time. Studies of industrial workers demonstrate that chronic exposure to mercury reduces the elimination rate of mercury.
“These results suggest that chronic mercury exposure has reached a critical level where inorganic mercury deposition within the human body is accumulating over time,” said Laks. “It is logical to assume that the risks of associated neurodevelopmental and neurodegenerative diseases will rise as well.”