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Higher Average Temperature Linked to Serious Vision Impairment Among Older Americans

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American adults 65 years old and older living in warmer regions are more likely to have serious vision impairment than their peers living in cooler regions, according to a recent study published in the journal Ophthalmic Epidemiology.  

Compared to those who lived in counties with average temperature of less than 50°F (< 10 °C), the odds of severe vision impairment were 14% higher for those who lived in counties with average temperature between 50-54.99°F, 24% higher for those between 55–59.99°F and 44% higher for those in counties with average temperature at 60°F (15.5 °C) or above.

“This link between vision impairment and average county temperature is very worrying if future research determines that the association is causal,” said first author Professor Esme Fuller-Thomson, “With climate change, we are expecting a rise in global temperatures. It will be important to monitor if the prevalence of vision impairment among older adults increases in the future.”  Dr Fuller-Thomson is the director of University of Toronto’s Institute of Life Course and Aging and is a Professor in the Factor-Inwentash Faculty of Social Work and the Department of Family and Community Medicine.

“We know that vision problems are a major cause of disabilities and functional limitations,” said co-author ZhiDi Deng, a recent pharmacy graduate from the University of Toronto, “Serious vision impairment, for example, can increase the risk of falls, fractures, and negatively impact older adults’ quality of life. Taking care of vision impairments and their consequences also cost the US economy tens of billions each year. So, this link between temperature and vision impairment was quite concerning.”

Impact of age, sex, income, and education

The relationship between average temperature and severe vision impairment was strong regardless of age, sex, income, and education of participants.

“It was powerful to see that the link between vision impairment and temperature was consistent across so many demographic factors including income.” says co-author Elysia Fuller-Thomson, a graduate student at the University of Toronto.

The association between higher county temperature and serious vision impairment was stronger for individuals aged 65 to 79 compared to those 80 or older, males compared to females, and White Americans compared to Black Americans.

Causes remain a mystery

The observed link between average temperature and severe vision impairment may be strong, but the mechanism behind this relationship remains a mystery.

The study’s authors hypothesise several potential causes for the observed relationship, including increased ultraviolet light exposure, air pollution, infections, and folic acid degradation with increased temperature. However, the design of this study does not provide definitive insight into how temperature affects vision. 

The study was based on six consecutive waves of the American Community Survey (2012–2017) which surveyed a nationally representative sample of American respondents aged 65 and older annually. The sample analysed included 1.7 million community-dwelling and institutionalized older adults in the coterminous US who lived in the same state in which they were born. The question on vision impairment was “Is this person blind or does he/she have serious difficulty seeing even when wearing glasses?” Average temperature data was obtained from the National Oceanic and Atmospheric Administration and combined with data from the American Community Survey.

“We were very surprised to discover this strong association between temperature and vision impairment,” said Esme Fuller-Thomson. “But this novel finding introduces more questions than it answers, including what the connection between average county temperature and vision impairment is. Moving forward, we plan to investigate whether county temperature is also associated with other disabilities among older adults such as hearing problems and limitations in daily activities.”

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