Indoor incense burning associated with poorer cognitive performance and decreased brain connectivity in older adults
A prospective 3-year longitudinal case-controlled study of 515 community-dwelling older adults in Hong Kong found that indoor incense burning was associated with poorer cognitive performance and decreased brain connectivity.
Incense is a mixture of fragrance materials and herbal, wood, and adhesive powders. When it is burnt, pollutants including particulate matter (PM), carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen dioxide (NO2), volatile organic compounds, aldehydes, and polycyclic aromatic hydrocarbons (PAHs) are released into the air. [Clin Mol Allergy 2008, doi: 10.1186/1476-7961-6-3; Sci Total Env 1996;193:149-158] “Incense burning is considered a major source of indoor air pollution; the amount of PM generated by incense can be up to 4.5 times of cigarettes,” wrote the researchers from the Chinese University of Hong Kong (CUHK). [Sci Rep 2020;10:7090]
Participants of the study were stroke- and dementia-free adults ≥65 years of age. Indoor incense use was self-reported as having burnt incense at home at least on a weekly basis over the past 5 years.
After adjustment for age, years of education, vascular risk factors and levels of outdoor pollutants in the participants’ residential areas, incense users had significantly poorer performance in measures of global cognition (Montreal Cognitive Assessment [MoCA] total score), executive functions (Symbol Digit Modalities Test and verbal fluency), visuospatial functions (MoCA visuospatial domain score) and memory (MoCA memory domain score and Rey Complex Figure Test 30-minute delayed recall) vs non-users.
Significant between-group differences persisted for MoCA total score, MoCA visuospatial domain score and MoCA memory domain score at year 3. “However, indoor incense burning was not associated with a more rapid decline in cognitive functions as measured by the MoCA total score,” noted the researchers.
“Although incense users did not have a higher frequency of diabetes mellitus [DM], hyperlipidaemia or white matter hyperintensities [WMH], significant interactions were observed between incense burning and DM [p=0.031], hyperlipidaemia [p=0.036] and WMH volume [p=0.008] on baseline MoCA total score, indicating that incense burning had a significantly more negative impact on global cognition in the presence of these risk factors,” reported the researchers.
Resting-state MRI revealed that incense users had significantly (p<0.05) decreased connectivity in the precuneus, medial frontal gyrus, left angular and right middle temporal gyrus. “Although indoor incense users did not have more structural brain changes in terms of small vessel disease lesions measured as WMH, lacune or median temporal lobe atrophy [imaging biomarker for Alzheimer’s disease], a subtle impact of incense burning on the brain was evident on the level of functional connectivity of the default mode network,” the researchers commented. “Indoor incense burning induces functional changes in the brain that may reduce cognitive resilience through functional connectivity alternation, and thereby may increase vulnerability to future cognitive decline.”
“Indoor incense burning may be detrimental to cognitive and brain health in community-dwelling older adults,” concluded the researchers. “Our findings have potentially far-reaching public health implications for cultures with widespread home use of incense, with a combined population size of 3.2 billion globally, and are particularly relevant to older adults given the potential links between indoor incense burning and vascular cognitive impairment. Results of this study call for safer practice of incense burning, for example, by avoiding burning incense indoors or using safer incense alternatives.”