The link between cadmium and smoking is clear, but researchers aren’t sure why nonsmokers also test high for the heavy metal.
By Gabe Rivin
A group of pregnant women in Durham County has been found to have high blood levels of cadmium, according to a new study from researchers at UNC-Chapel Hill and the University of Michigan.
But while the researchers noted that a surprisingly large number of pregnant women in the study smoked cigarettes, which contain cadmium, even the nonsmokers in the study had high levels of the element in their blood. But the reason for the exposure in nonsmokers was unclear.
Cadmium, a heavy metal, has been linked to miscarriages and low birth weight, in addition to lung cancer and kidney disease.
According to UNC professor Rebecca Fry, one of the researchers involved in the study, cadmium can harm humans even at low levels.
“Cadmium is a toxic metal and serves no function in cells,” Fry said. “So any level can be potentially harmful.”
Focusing on lower exposures
Cadmium has a long history of study among health researchers. For years, it’s been a concern for workers in manufacturing plants, such as refrigeration compressor plants and battery factories.
Researchers have accumulated a dizzying list of the ways cadmium can harm human health. Cadmium can cause lung cancer and kidney damage, according to the U.S. Occupational Safety and Health Administration. Inhaling large amounts can have severe, even fatal, effects on the respiratory system. Some studies have linked cadmium to prostate cancer.
Yet in recent years, health researchers have begun looking at chronic, low-level exposure to heavy metals such as cadmium, according to Carmen Marsit, a professor in Dartmouth College’s school of medicine.
“A lot of the older literature was focused on more industrial accidents, or major pollution events, or very highly exposed regions of the world,” he said. “Now we’re starting to think about it in areas where we may have lower levels of exposures.”
Marsit said that this sort of research has increasingly focused on pregnant women.
“The developmental period is a time when there’s rapid differentiation of cells as the fetus develops,” he said. “At any point along that line, if an exposure in any way can disrupt the way that that process happens, you can imagine that that can lead to various types of health effects, and that they may have long-lasting implications.”
Fry’s recent study doesn’t specifically link cadmium to any health effects. But she and her colleagues are preparing to release a new study that does.
The study, which is about to be published by PLoS ONE, links mothers’ blood levels of cadmium to lower birth weights among their babies. Fry said her group observed these effects at varying levels of cadmium in the women’s blood.
“Every individual can respond differently, even to very low doses of a toxic metal,” she said.
A surprising number of smokers
Fry, along with colleagues from the University of Michigan tracked 1,229 pregnant women in Durham from 2005 to 2010. The women received care at either Duke University’s obstetrics clinic or Durham County Public Health’s Prenatal Clinic, and had their blood sampled between weeks 23 and 42 of their pregnancy.
The researchers found that about 60 percent of participants exceeded the U.S.’s median blood level for cadmium, which is 0.32 micrograms per liter. Among smokers, cadmium was measured as high as 4.02 micrograms per liter, more than 12 times the national median, while nonsmokers’ measurements reached up to 2.26 micrograms per liter.
Smoking carries a number of dangers for pregnant women, according to the Centers for Disease Control and Prevention. It increases the risk of miscarriages, premature births, cleft lips and Sudden Infant Death Syndrome, among other problems. Still, the study found that about 25 percent of the pregnant women followed were smokers. On average, smokers in the study were found to have twice as much cadmium in their blood as nonsmokers.
Fry said she was struck by the number of women who still smoked while pregnant.
But the study also found that 53 percent of nonsmokers had cadmium levels above the U.S. median. The researchers didn’t offer a clear explanation for this, but said that the women could have been exposed to cadmium from the food they ate or industrial sources nearby.
According to the U.S. Environmental Protection Agency, the main sources of airborne cadmium are coal- and oil-fired power generation and the burning of municipal waste. The EPA also says that food can have increased amounts of cadmium when farmers apply phosphate fertilizers or sewage sludge to their crops.
Fry added that private water wells could also have exposed the Durham women to cadmium. But she made clear that the researchers don’t yet have a clear explanation about the cadmium measurements in nonsmokers.
Translating research to medical advice
“We are aware of the fact that academic research often takes a long time to translate into the average OB/GYN’s practice or the pediatricians’ practice or medical practice in general,” said Kevin Ryan, who recently stepped down as the head of the women’s and children’s health section at the N.C. Department of Health and Human Services. “We try to make sure we have mechanisms in place that effectively translate important research into practice.”
Those mechanisms, he said, include the Perinatal Quality Collaborative, a statewide group that includes neonatologists and obstetricians, and which tracks research. The group issues best-practice recommendations to health care providers.
And though DHHS doesn’t have immediate plans to act on the cadmium study, it does offer a number of programs that can help women to quit smoking, Ryan said.
Every local health department, for example, must offer prenatal care that includes counseling to help women quit smoking, according to Belinda Pettiford, who heads the women’s health branch within DHHS’s women’s and children’s health section. The same is true for clinics that offer family-planning services.