Many people believe that avoiding smoking is enough to protect themselves from the dangers of cigarettes.
However, scientists continue to find evidence that simply breathing in other people’s cigarette smoke can also harm health.
A new study has found that adults exposed to secondhand cigarette smoke carry significantly higher levels of cadmium in their bodies. On average, they have about 1.5 times more of this toxic metal in their blood than adults who live in smoke-free environments.
The research was carried out by scientists at Texas A&M University’s School of Public Health and published in the journal Biological Trace Element Research.
Cadmium is not a nutrient that the human body needs. Instead, it is a toxic heavy metal that can damage organs and tissues over time.
Scientists have linked cadmium exposure to kidney disease, bone problems, breathing disorders, and several types of cancer. Unlike many substances that can be removed relatively quickly, cadmium stays inside the body for many years and gradually accumulates.
This long-term buildup is what makes cadmium especially concerning. Small exposures repeated over many years can eventually contribute to serious health problems.
Researchers have known for a long time that cigarette smokers absorb cadmium because tobacco plants naturally take up the metal from the soil. When tobacco is burned, cadmium enters the smoke and can be inhaled into the lungs.
However, until now, scientists did not know clearly whether secondhand smoke also contributed significantly to cadmium exposure.
To investigate the issue, researchers analyzed health information from more than 5,000 participants across the United States between 2015 and 2020. The study included 3,686 adults and 1,380 children and teenagers.
The researchers collected blood and urine samples and measured both cadmium and cotinine levels. Cotinine is produced when the body breaks down nicotine and is widely used as a marker of recent tobacco smoke exposure.
Blood samples helped reveal recent exposure to cadmium, while urine samples provided information about long-term accumulation because the kidneys can store cadmium for up to three decades.
Participants were classified according to their smoke exposure levels, ranging from no exposure to active smoking.
Among adults, the findings were clear. Cadmium levels increased as exposure to cigarette smoke increased. Active smokers had more than three times as much cadmium in their blood compared with nonsmokers. Even adults who did not smoke but were heavily exposed to secondhand smoke had substantially higher cadmium levels.
The findings suggest that secondhand smoke may quietly expose people to harmful contaminants even if they never touch a cigarette.
The researchers found different results among children and teenagers. In younger participants, cadmium levels did not vary significantly according to tobacco smoke exposure.
One possible explanation is that cadmium builds up slowly over time. Adults have experienced many more years of exposure and therefore may carry a greater lifetime burden of the metal. In addition, kidneys become less efficient with age, making it harder to eliminate cadmium from the body.
Another interesting finding was the difference between men and women. Women consistently had higher cadmium levels than men. Researchers explained that female biology allows cadmium to be absorbed more efficiently through the digestive system. Hormonal changes during menstruation, pregnancy, and menopause may further increase absorption.
The study also pointed to important social inequalities. People from racial minority groups and those with lower incomes or lower educational attainment tended to have higher exposure levels.
The reasons are likely complex. Some people may live in apartment buildings where cigarette smoke spreads between units through ventilation systems.
Others may face additional environmental exposures from food contamination, polluted soil, or traffic emissions. Limited access to health information and smoking cessation resources may also contribute to these differences.
The study has important strengths. It used objective biological measurements and included a large number of participants from national health surveys. These features make the findings more reliable.
However, the researchers also acknowledged several limitations. Cotinine remains in the body for less than a day, making it difficult to determine long-term smoking patterns from a single test. The study also could not track cadmium intake from food and environmental sources over many years.
Most importantly, the research shows an association rather than direct proof of cause and effect. Additional long-term studies will be needed to fully understand how secondhand smoke contributes to cadmium accumulation.
Even with these limitations, the study delivers a powerful message. Secondhand smoke may expose nonsmokers to a toxic metal that can remain in the body for decades.
Protecting people from cigarette smoke is therefore important not only for lung health but also for reducing exposure to dangerous environmental contaminants that can slowly damage health over a lifetime.
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Source: Texas A&M University.
