More research is needed to confirm the findings, the researchers say.
The study, led by Yi-Hao Peng, Department of Respiratory Therapy, China Medical University Hospital, Taichung, Taiwan, was published online Sept. 30 in the Journal of Epidemiology and Community Health.
Researchers identified almost 13,000 people with asthma diagnosed between 2001 to 2003. For each person with asthma, they selected four other people with similar characteristics, such as age and gender, for a comparison group of 51,084.
People with asthma had a higher odds of getting dementia, the study found. This result differs from that of a previous study in Sweden that didn't find asthma raises risk for Alzheimer's disease. This, said the researchers of the current study, may be because that earlier study was based on self-reports instead of doctor diagnoses, which makes it less reliable.
Overall, men had higher rates of dementia than women. The risk was lower for women even after the researchers took into account age, other conditions, annual outpatient doctor visits, and oral corticosteroid use.
The elderly had a significantly higher risk for dementia than younger people with asthma, a finding that fits with those of previous studies and confirms that age is one of the strongest risk factors for dementia.
People with a history of a stroke had the highest risk for dementia, followed by those with atrial fibrillation; more than 30 annual doctors’ visits; head injury; diabetes; high blood pressure, and high cholesterol and blood fat levels. The study also indicated that the risk for dementia rises with the number of asthma-related emergency department visits and admissions to the hospital.
Theories About the Link
The authors outlined several possible things connecting asthma and dementia. One theory is that both conditions involve inflammation.
Another theory is that the lungs in people with asthma may lead to an ongoing lack of oxygen, and then to abnormal production of brain chemicals leading to dementia. They also speculate that steroid use in people with asthma may speed up brain shrinkage, raising dementia risk.
Interestingly, though, the study showed that people taking inhaled steroids to control their asthma had a significantly lower risk of dementia compared to those with asthma not taking these medications.
This work was supported by the study projects in China Medical University; Taiwan Ministry of Health and Welfare Clinical Trial and Research Center of Excellence; and health and welfare surcharge of tobacco products, China Medical University Hospital Cancer Research Center of Excellence (Taiwan).