Blood lead levels are associated with increased blood pressure and the risk of clinical hypertension in women aged 40 to 59 years, according to a team of researchers from the Johns Hopkins Bloomberg School of Public Health, University of Maryland School of Medicine, Tulane University and the Centers for Disease Control and Prevention.
The study found blood pressure increased by lead levels well below the exposure levels of concern for adults set by the Occupational Safety and Health Administration and the levels for children set by the CDC. Blood lead levels can increase in women over the menopause, as lead is released from bone. The study is the first to document adverse health impacts as a consequence of bone lead release. It is published in the March 26 edition of the Journal of the American Medical Association.
"This study really underscores the consistent finding by public health researchers that there is no known threshold of lead exposure with regard to its effects on human health," explains lead author Denis Nash, a researcher with the New York City Department of Health and Mental Hygiene and a graduate of the School of Public Health. "While lead levels continue to decline in the United States, these results also have implications for populations with higher environmental lead exposure, mostly in developing countries, which still use leaded fuel and where the blood lead levels are still quite high. The study provides support for continued efforts at reducing environmental lead exposure in the U.S. population, even low levels of lead exposure, in populations," Nash says.
The study included 2,165 women aged 40 to 59 who took part in the Third National Health and Nutrition Examination Survey conducted between 1988 and 1994. After adjusting for factors known to be associated with blood pressure such as age, race, ethnicity, alcohol use, cigarette smoking, body mass and kidney function, the researchers found a significant association between blood lead and increased systolic and diastolic blood pressure. The association was greatest among postmenopausal women, compared with other women in the study.
Blood lead levels varied greatly among the study participants with the average being 2.9 micrograms of lead per deciliter of blood. Women in the highest quartile of the study group, with an average blood lead of 6.3 micrograms, were at three times greater risk of diastolic hypertension compared to women in the lowest quartile with an average lead level of 1 microgram per deciliter. The limit set by OSHA for safe occupational exposure is 40 micrograms per deciliter, while the level of concern for childhood lead poisoning is 10 micrograms per deciliter.
Overall, the researchers found that the changes in blood pressure associated with blood lead were small and would be considered normal. While the study does not suggest that low levels of lead in the blood are the leading cause of hypertension, the researchers say it could be responsible for or contribute to a significant number of cases of hypertension in the general population. An earlier study by Silbergeld's group, published in the journal Archives of Internal Medicine in December 2002, found associations between lead and risks of death from cardiovascular disease in both men and women.
"These risks are particularly important for women," says co-author Ellen Silbergeld, professor in the school's Department of Environmental Health Sciences. "As young children, women in their 40s and 50s, like men, were exposed to lead from its use in gasoline, paints and plumbing. However, women, unlike men, run the risk of re-exposures at menopause when lead is remobilized from bone back into the blood. This study indicates that this re-exposure may be significant for women's health."
Funding for the study was provided by the Centers for Disease Control and Prevention and the Association of Teachers of Preventive Medicine co-operative agreement by the Heinz Foundation.