Unveiling a delicate balance: New research shows that both too much and too little selenium and manganese in the blood can sharply increase the risk of death in asthma patients.
Study: Association between blood heavy metal element and all-cause mortality in asthmatic adults: a cohort study. Image Credit: WESTOCK PRODUCTIONS / Shutterstock
Scientists at the Chongqing Medical University, China, have conducted a study to investigate the association between blood levels of heavy metals and all-cause mortality among adult patients with asthma.
The study is published in the journal Scientific Reports.
Background
Asthma is a respiratory disease caused by bronchospasm and airway inflammation. The most common symptoms are breathing difficulty, chest constriction, wheezing, coughing, and thick mucus production.
The prevalence of asthma is increasing steadily worldwide, partly because of increasing environmental exposure to allergens, air pollutants, and tobacco smoke. Currently, more than 350 individuals are living with asthma worldwide, and around 250,000 annual fatalities are directly linked to the condition.
Heavy metals, including lead, cadmium, mercury, and manganese, are ubiquitous in the environment and can enter the lungs and bloodstream through ingestion of food or water and inhalation of polluted air. Exposure to these heavy metals can trigger inflammation and oxidative stress, which in turn can cause lung damage and premature death.
Selenium is a micronutrient that plays a vital role in reducing oxidative stress and improving immune response. It has a multifactorial relationship with respiratory diseases, including asthma. Existing evidence indicates that low blood levels of selenium increase the risk of developing asthma; however, both deficient and excessive levels of selenium can be harmful.
In this study, scientists have evaluated the associations between blood levels of heavy metals and all-cause mortality in adult asthma patients.
Study design
The study analyzed data from the National Health and Nutrition Examination Survey (NHANES), a scientific effort carried out by the US Centers for Disease Control and Prevention (CDC) between 2011 and 2018.
The scientists screened NHANES data and identified 2,432 adult asthma patients for the study analysis. They obtained patient data on blood levels of certain heavy metals, including lead, cadmium, mercury, selenium, and manganese.
They determined the survival status of participants by matching survey data with the National Death Index (NDI) as of December 31, 2018. They also used the 10th edition of the International Statistical Classification of Diseases (ICD) ten to determine the all-cause mortality status.
They examined the association between blood heavy metal levels and all-cause mortality risk after adjusting for potential confounding factors, including sociodemographic characteristics, body mass index (BMI), smoking and alcohol intake status, and the presence of comorbidities.
Important observations
The analysis of baseline characteristics of participants revealed that mortality among asthma patients is associated with older age, lower educational and financial status, smoking status, and the presence of cardiometabolic and pulmonary diseases and malignancies.
The study found that a higher blood selenium level is associated with a significantly lower all-cause mortality in asthma patients. In contrast, a significant positive association was observed between blood manganese level and all-cause mortality among participants. However, it is important to note that the study found a significant U-shaped relationship for both selenium and manganese, indicating that both very low and very high levels of these metals are associated with higher mortality.
Regarding other tested heavy metals (lead, cadmium, and mercury), the study suggested possible relationships between these metals and mortality in initial analyses. However, these associations did not remain significant in the final multivariate analysis, indicating that their effects may be masked by confounding factors or require more complex mechanisms to explain.
The analysis controlling for potential confounding factors revealed a 10% reduction in all-cause mortality for every additional ten units of blood selenium (micrograms/liter). In contrast, a 6% induction in all-cause mortality was noted for every additional unit of blood manganese (micrograms/liter).
The U-shaped association observed between blood selenium, blood manganese, and all-cause mortality suggests that asthma patients with either very high or very low selenium and manganese levels in the blood are at a higher risk of all-cause mortality. The lowest all-cause mortality was observed in asthma patients with blood selenium and manganese levels of 188.66 and 8.47 micrograms/liter, respectively.
Among tested heavy metals, selenium had the highest positive impact on the survival status of asthma patients.
Study significance
The study finds an inverse association between blood selenium level and all-cause mortality and a positive association between blood manganese level and all-cause mortality in adults with asthma.
The significant U-shaped association between selenium and manganese emphasizes the crucial importance of maintaining these metals within an optimal range. Both deficiency and excess pose risks to health, underscoring the importance of balanced dietary intake and careful management of exposure to these elements.
Manganese acts as a cofactor for many enzymes, including manganese superoxide dismutase. It also serves as a structural component in certain enzymes involved in metabolic pathways. However, excessive accumulation of manganese in the blood can lead to a pathological induction of intracellular autophagic pathways and an impairment of energy metabolism, which in turn can damage respiratory airways and increase the risk of death in asthma patients.
Selenium is an essential micronutrient required for the activity of various antioxidant enzymes and immune cells, including T helper cells. While selenium supports many vital functions, excessive intake has toxicological consequences, including damage to the respiratory, digestive, and cardiovascular systems.
Overall, the study findings suggest that optimizing dietary selenium intake and managing manganese exposure can potentially improve health outcomes in adult individuals with asthma. It also provides valuable insights into the relationship between blood metal levels and mortality in asthma patients, contributing to understanding how these elements influence long-term health outcomes.
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