Twenty years ago, scientist Ellen Silbergeld helped prove that lead in gasoline harmed people terribly, then helped rid the United States of the danger. Now she has discovered that although that lead may be forgotten, it's not altogether gone.
A new national study conducted by the University of Maryland professor shows that post-menopausal women are finding a sudden, dramatic increase of lead in their blood. Levels can rise an average of 30 percent, Silbergeld says, an increase that also raises the women's risk for hypertension and heart attacks.
The lead is coming from sources that have been stored for many years in women's bones, a supply that reflects the effects of growing up in the era of leaded gas guzzlers.
Silbergeld's research shows that the rise of lead in the bloodstreams of older women is due to their bodies' losing bone minerals, a menopause-related process that also releases lead into the bloodstream. The good news is that a regimen of hormone replacement therapy -- treatment used to prevent bone loss -- also seems to keep lead from leaving the bone.
The toxicologist, who directs the Program of Human Health and the Environment at the University of Maryland School of Medicine, will present her findings Friday at a scholarly symposium in Baltimore about environmental dangers to women's health.
Her study of post-menopausal women aged 40 to 55 is based upon data from the National Health and Nutrition Examination Survey, part of a continuing effort by the Centers for Disease Control and Prevention to provide statistically accurate health portraits of the nation.
Baby boomers were exposed to leaded gasoline (not banned until 1983) while their bones were forming, Silbergeld says.
And as a baby boomer herself, the 53-year-old researcher takes the news quite personally.
"One could argue that we may have the highest amount of lead in our bones [of any generation] because we grew up during the absolute heyday of lead in gasoline," she says.
Although men also have lead stored in their bones, they are not generally at risk for bone loss until their 70s, Silbergeld says. And even then, they will not lose bone minerals as dramatically as women do.
An authority on how exposure to toxic substances can affect human health, Silbergeld became interested in examining how lead, which the body stores the same way it does calcium, emerges into women's systems during pregnancy and menopause, which can significantly affect calcium levels. About 90 percent of the lead in human bodies is stored in the bones.
"Just as bone is dynamic at turning up and releasing calcium, it's dynamic at turning up and releasing lead," she says. "We had thought of bone as a storage spot, but it's not a permanent spot."
In comparing two studies of adult women taken in the 1980s and '90s, Silbergeld found that the overall lead levels in women have decreased by about 60 percent, traceable to an environment improved by unleaded gasoline. What was happening inside the women's bones, however, remained comparable: Both groups saw a post-menopausal 30 percent increase of blood lead levels.
"We found a very strong relationship between blood lead levels and blood pressure in postmenopausal women," she says. "Increases of blood lead levels are strongly associated with increased risks of heart attack, angina and hypertension. And this is after controlling for all the things you want to control for, such as age, body weight, cholesterol levels.
"Our finding is that lead is a strong risk factor for cardiovascular disease in older women.
"How much lead is in your bones is one of the factors that will determine how much your blood lead level will increase after menopause," she says.
"What baby boomers are getting now is the blast from the past. Or, as a friend of mine says, we're 'the walking time bombs of our generation.' "
Although the bones of women aged 30 to 50 show elevated levels of lead, there are no standards to evaluate the danger this poses. Existing definitions of lead poisoning apply only to levels of lead in the blood.
"We now understand that the lead in bone is an important source for re-exposure to lead," Silbergeld says. "But we know nothing at all about what lead in bone means for the health of the bone. We have just not thought about it, although researchers are now looking into it."
When it comes to lead in the blood, current standards recognize the danger point as 10 micrograms per deciliter for children and 35 micrograms per deciliter for adults. Silbergeld thinks the adult standard, from 1976, is "very out of date" and too liberal.
At those levels, the recommended treatment is to remove a person from the source of exposure and begin chelation therapy, using a drug that binds to lead to remove it from the body.
The post-menopausal women in Silbergeld's study have lead levels below the currently set danger point. Their levels rose from a range of 3 to 5 micrograms to a range of 4 to 7 micrograms -- a bump sufficient enough to put them at greater risk of heart problems, she says. However, researchers do not yet know if chelation therapy is effective at removing blood lead at these levels.
Meanwhile, the scientist recommends that post-menopausal women consider taking hormone replacement therapy because her study indicated that those women who did not use it had higher blood lead levels.
She hopes the women's health conference, which is partly sponsored by her department, will expand thinking about other hazards women encounter at home and on the job.
"In the jobs that we classically think of as being 'women's work' -- cosmetology, health care and secretarial work -- there are risks. Clerical workers have ergonomic problems with computers. Cosmetologists have to work daily with chemicals, often in very badly ventilated spaces. Health care workers have enormous injury rates often related to lifting and moving patients.
"We also want them to consider the effects of the stresses of the multiple roles women play as caregivers, as mothers, as partners."
Maureen Hatch, director of epidemiology at Mount Sinai School of Medicine in New York, will consider how stress affects menstrual function, pregnancy complications and outcomes, the immune system and such chronic diseases as hypertension and breast cancer.
Other researchers will discuss women's exposure to pesticides and other indoor pollutants, examine the risk factors for uterine fibroids -- which appear to be increasing -- and also look at the role environmental estrogens may play in lowering the age of female puberty.