A new study finds that adults who simply breathe in secondhand cigarette smoke have about 1.5 times more of the toxin cadmium in their blood than people in smoke-free environments.
"We knew that cigarette smoke exposes people to cadmium, but until now, we didn't know about the association with secondhand smoke," said Nandita Sarker, a doctoral student in the Department of Environmental and Occupational Health at Texas A&M University's School of Public Health and the study's first author. "This is important information because cadmium builds up in the body over time and is a factor in kidney, lung and prostate cancers."
Even though fewer people smoke today, tobacco use remains a major public health concern. In addition to being a known cause of cancer , cadmium can lead to kidney failure, brittle and painful bones and chronic breathing issues such as bronchitis and asthma.
For their cross-sectional study, published in Biological Trace Element Research, the researchers assessed cadmium levels in the blood and urine of 1,380 children and teenagers and 3,686 adults using national health data from 2015 to 2020. To determine recent tobacco smoke exposure, the researchers measured the levels of cadmium and nicotine (measured as cotinine ) in the subjects' systems and categorized them as no exposure, light exposure, heavy exposure and active smoking.
Both blood and urine were measured because blood is a highly effective tool for determining recent exposure to cadmium, while the kidneys retain cadmium for up to 30 years, making urine an accurate record of any long-term accumulation of cadmium.
Statistical analyses led to these key findings:
- Adults: The more smoke adults were exposed to, the more cadmium they had in their blood. Active smokers had over three times more cadmium in their blood than nonsmokers, while those with heavy secondhand smoke exposure had about 1.5 times more.
- Children and teenagers: Cadmium levels did not change significantly based on smoke exposure for younger people. The contrast with adults could be because cadmium levels naturally increase with age simply because the kidneys accumulate the metal over a lifetime and become less efficient at clearing it out.
"In short, breathing in cigarette smoke — either from active smoking or secondhand exposure — significantly raises toxic cadmium levels in adults," Sarker said.
Biological sex also plays a role. Across all age groups, women consistently exhibited higher cadmium levels than men. This difference comes down to basic biology: the female digestive tract naturally absorbs cadmium much more efficiently than the male digestive tract and this is even more the case during major hormonal shifts like menstruation, pregnancy and menopause.
In addition, the study found that people in a racial minority group or who have lower income or less education face significantly higher exposure to cadmium.
"This disparity cannot be explained by smoking habits alone, but likely is the result of broader social, environmental and financial inequalities," Sarker said. "In these cases, the cadmium typically comes from crowded, multi-unit housing where smoke spreads through shared ventilation systems or from food, soil and traffic exhaust."
She added that people with less education often have only limited access to health warnings, making it harder to join smoking cessation programs.
"Our findings suggest that secondhand smoke may contribute to the long-term accumulation of cadmium, a toxic metal associated with cancer and other chronic diseases," said Taehyun Roh , with the Department of Epidemiology and Biostatistics who supervised the study. "These results highlight the importance of protecting people from tobacco smoke exposure not only for respiratory health, but also for reducing exposure to harmful environmental contaminants that can accumulate in the body over time."
Sarker noted that while the study's size, objective measurements and consideration of demographic variables ensured accurate results, a few limitations remain.
"Cotinine only stays in the human body for about 15 to 20 hours, and this short window means a single lab test cannot distinguish between someone who just walked out of a heavily smoke-filled room and an occasional active smoker, nor can it track dietary cadmium intake over several decades," Sarker said. "Follow-up studies that track people over longer periods will provide more insight into cause and effect."
Others involved in the study were Garett Sansom with the Department of Environmental and Occupational Health and Nusrat Fahmida Trisha and Nishat Tasnim Hasan with the Department of Epidemiology and Biostatistics. Sansom and Roh also are affiliated with the Texas A&M Interdisciplinary Faculty of Toxicology .
By Ann Kellett, Texas A&M University School of Public Health
