In a recent study published in BMC Public Health, researchers examine the correlation between blood cadmium (Cd) exposure and sleep disturbances, as well as the role of physical activity on mitigating these effects.
Study: Mitigation role of physical exercise participation in the relationship between blood cadmium and sleep disturbance: a cross-sectional study. Image Credit: SB Arts Media / Shutterstock.com
Heavy metals like Cd, mercury (Hg), and lead (Pb) are widely found throughout the environment because of their use in electronics, optics, and medical industries. As a result, many heavy metals can enter the human system through the ingestion of contaminated water and food, inhalation of ambient air, and skin contact.
Previous studies have demonstrated that heavy metal toxicity contributes to the development of neurological diseases such as stroke, Alzheimer's disease, and sleep disturbances. The effect of toxic metals on brain and sleep health is a growing area of research due to the increased prevalence of poor sleep and sleep disturbances in modern society. In fact, about one-third of the United States population self-reports trouble in sleeping.
To date, research has been limited in explaining the etiology of sleep-related disorders. Nevertheless, physical exercise (PE) appears to improve sleep quality and efficiency through various biological and psychosocial mechanisms.
About the study
Data was collected from the National Health and Nutrition Examination Survey (NHANES) conducted by the National Center for Health Statistics. A total of 8,751 participants were included in the current study.
Whole blood samples were obtained from all study participants and analyzed for Cd, Pb, and Hg levels through inductively coupled plasma-mass spectrometry (ICP-MS). The study participants also provided information on their demographics, socioeconomics, physiological, biochemical, and health concerns. The presence of sleep disturbances was also determined by self-reports and interview responses.
NHANES defined PE as leisure time or recreational physical engagement in the form of sports, fitness, or other recreational activities. Physical activity levels were classified as none, low, and moderate-to-vigorous based on the number of days and minutes of exercise an individual participates in a typical week.
Of the 8.751 adults over the age of 20 who were included in the current study, about 48% were men with a median age of 50 years. Moreover, over 50% of the study cohort were non-Hispanic White and married, had completed a college education or higher, had a higher income, and were less likely to be diabetics or cardiovascular patients.
About 25% of the study cohort reported sleep disturbances. A positive correlation was observed between study participants with blood Cd levels exceeding 1.68 µg/L Cd and sleep disturbances, whereas no statistically significant relationship was observed between Pb or Hg blood levels and risk of sleep disturbances.
More specifically, the effect of exposure to Cd, Hg, and Pb on sleep disturbances was 89.1%, 10.8%, and 0.1%, respectively. Taken together, these findings demonstrate that Cd exposure is associated with the greatest risk of sleep disturbances as compared to Hg or Pb exposure.
Females were found to be at a greater risk of sleep disturbances than males. Additionally, non-Hispanic White, non-Hispanic Black, and Mexican Americans were at a greater risk of Cd exposure and sleep disturbances.
Additional demographic factors that increased the risk of sleep disturbances with notable blood Cd levels included those who were older than 60 years of age, body mass index (BMI) values exceeding 30 kg/m2, smokers, education level below high school or above college, unmarried, worse family income, alcohol consumption, and a diagnosis of cardiovascular disease.
The weighted logistic regression analyses revealed significant negative associations between moderate-to-vigorous physical exercise (MVPE) and sleep disturbances; however, no significant association was observed between low exercise levels and sleep disturbances. When higher levels of Cd exposure and the presence of sleep disturbances were considered, the MVPE group had a lower risk of sleep disturbances than the non-exercise group.
Strengths and limitations
The general population design, large sample size, and survey-weighted analytical methods based on complex multistage sampling are key strengths of the current study. However, some notable limitations include the mixed-model approach used for only three specific metals rather than all metals. Moreover, the survey results were based on self-reported interviews, which may be biased.
Additional research is needed to determine the impact of exercise and heavy metal exposure on sleep disturbances in other groups like industrial workers, chemical plant workers, and children.
Higher Cd levels within the blood were significantly associated with sleep disturbances, even when considering various confounding factors, whereas Pb and Hg exposure was not found to impact the risk of sleep disturbances. The study findings also demonstrate the benefits of exercise on mitigating the risk of Cd exposure on sleep disturbances.