Asthma associated with increased risk for Alzheimer’s disease

Key takeaways:

• Asthma was linked to 20% to 33% higher 2-year incidence of Alzheimer’s disease.
• Future research should investigate use of biologics and improving asthma control to mitigate Alzheimer’s disease development.

The incidence and prevalence of Alzheimer’s disease was positively associated with an increased risk for asthma, according to a study published in The Journal of Allergy and Clinical Immunology.

“A study from Taiwan had suggested higher rates of Alzheimer’s in patients with asthma,” Christie Bartels, MD, MS, division head and associate professor in the division of rheumatology, department of medicine, University of Wisconsin School of Medicine and Public Health, told Healio. “This prompted us to question whether similar increases would be observed in the U.S.”

The study used a 20% random sample from a national Medicare database between 2013 and 2015. A comparison was made between adult patients with asthma and those without asthma who were both on more than 12 months of continuous Medicare.

Researchers defined asthma by the presence of one inpatient or two outpatient codes for asthma. The main outcomes of the study were 2-year incident or prevalence of Alzheimer’s disease (AD).

In total, the cohort included 5,460,732 Medicare beneficiaries, with 678,730 (mean age, 69.6 years; 67.7% women; 83% white) having baseline asthma. The asthma patients more often identified as Black and as having prior Medicaid eligibility compared with the patients without asthma. They were also more likely to live in disadvantaged neighborhoods and have cardiovascular disease and comorbidity.

Researchers found that a 2-year incidence of AD was 1.4% with asthma and 1.1% without asthma (P .001). Over the 2 years, per 100,000 patients, 303 more incident AD cases were seen in patients with asthma, with 1,408 cases with asthma compared with 1,105 cases without asthma (P < .001).

The 2-year incidence of dementia was 6.5% with asthma and 4.4% without asthma (P .001). Over the 2 years, per 100,000 patients, 2,060 more incidents of dementia occurred in patients with asthma.

The overall prevalence of AD in asthma patients was 7.8% compared with patients without asthma at 5.4% (P < .001). There were 2,425 more prevalent cases found in those with asthma, with 7,834 patients having asthma and 5,409 without asthma (P < .001).

Among patients with asthma, the prevalence of dementia was 20.3% compared with 12.9% in patients without asthma (P .001). Per 100,000 patients, prevalence showed 7,368 more cases of dementia in those with asthma (P < .001).

Multivariable models showed that asthma had bigger odds for a 2-year AD incidence with an adjusted odds ratio of 1.33 (95% CI, 1.29-1.36). Asthma also was linked to higher AD prevalence (aOR = 1.44; 95% CI, 1.42-1.46).

“The magnitude of observed increases in Alzheimer’s in asthma even after controlling basic sociodemographics was surprising,” Bartels said. “We observed an appoximately 30% increased incidence (aOR = 1.33; 95% CI 1.29-1.36) and nearly 50% greater prevalence (aOR = 1.44; 95% CI, 1.42-1.46) of Alzheimer’s in asthma among 5 million U.S. Medicare patients.”

Bartels also noted that some studies have found rheumatoid arthritis is linked to an increased risk for Alzheimer’s disease, whereas treating this condition with anti-TNF agents is linked to a decreased risk. This, in addition to their study’s findings, raises questions of whether biologic treatment of asthma could mitigate risk for Alzheimer’s.

“Combining our findings with prior reports in [rheumatoid arthritis], one could hypothesize that controlling inflammation aggressively and using steroid-sparing therapies might reduce Alzheimer’s risk,” Bartels said.

She also emphasized that future studies should investigate how asthma control and biologic treatment can potentially impact increases in Alzheimer’s risk.