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LONDON — Smoking may be the most influential factor in whether older adults go on to develop dementia. That's the concerning takeaway from a groundbreaking study spanning 14 European countries. Researchers in London have found that when it comes to maintaining cognitive function as we age, the biggest impact may come from a single lifestyle choice: not smoking.
The study, published in Nature Communications, followed over 32,000 adults between 50 and 104 for up to 15 years. While previous research has often lumped various healthy behaviors together, making it difficult to pinpoint which ones truly matter, this study took a different approach. By examining 16 different lifestyle combinations, the researchers were able to isolate the effects of smoking, alcohol consumption, physical activity, and social contact on cognitive decline.
The results were striking. Regardless of other lifestyle factors, non-smokers consistently showed slower rates of cognitive decline compared to smokers. This finding suggests that quitting smoking - or never starting in the first place - could be the most crucial step in preserving brain function as we age.
“Our findings suggest that among the healthy behaviors we examined, not smoking may be among the most important in terms of maintaining cognitive function,” says Dr. Mikaela Bloomberg from University College London in a media release.
“For people who aren’t able to stop smoking, our results suggest that engaging in other healthy behaviors such as regular exercise, moderate alcohol consumption and being socially active may help offset adverse cognitive effects associated with smoking.”
Methodology: Unraveling the Cognitive Puzzle
To understand how the researchers arrived at this conclusion, let's break down their methodology. The study drew data from two major aging studies: the English Longitudinal Study of Ageing (ELSA) and the Survey of Health, Ageing and Retirement in Europe (SHARE). These studies are treasure troves of information, following thousands of older adults over many years and collecting data on their health, lifestyle, and cognitive function.
The researchers focused on 4 key lifestyle factors:
- Smoking (current smoker or non-smoker)
- Alcohol consumption (no-to-moderate or heavy)
- Physical activity (weekly moderate-plus-vigorous activity or less)
- Social contact (weekly or less than weekly)
By combining these factors, they created 16 distinct lifestyle profiles. For example, one profile might be a non-smoker who drinks moderately, exercises weekly, and has frequent social contact, while another might be a smoker who drinks heavily, doesn't exercise regularly, and has limited social interaction.
To measure cognitive function, the researchers used two tests:
- A memory test, where participants had to recall a list of words immediately and after a delay
- A verbal fluency test, where participants named as many animals as they could in one minute
These tests were repeated at multiple time points over the years, allowing the researchers to track how cognitive function changed over time for each lifestyle profile. To ensure they were capturing the effects of lifestyle rather than early signs of dementia, the researchers excluded anyone who showed signs of cognitive impairment at the start of the study or who was diagnosed with dementia during the follow-up period.
Key Results: Smoking Takes Center Stage
When the researchers crunched the numbers, a clear pattern emerged. Across the board, lifestyles that included smoking were associated with faster cognitive decline, regardless of other factors. For example:
- Smokers who had heavy alcohol consumption, infrequent exercise, and limited social contact showed the fastest rate of cognitive decline.
- Even smokers who followed all other healthy behaviors (moderate drinking, regular exercise, and frequent social contact) still showed faster cognitive decline than non-smokers.
- Among non-smokers, differences in other lifestyle factors had much smaller effects on cognitive decline.
To put this in perspective, over a 10-year period, smokers' memory scores declined up to 0.17 standard deviations more than non-smokers, and their verbal fluency scores declined up to 0.16 standard deviations more. While these numbers might seem small, they could translate to noticeable differences in daily cognitive function over time.
Interestingly, the effects of other lifestyle factors were less pronounced. Moderate alcohol consumption was associated with slightly slower cognitive decline compared to heavy drinking, but the difference was much smaller than that seen with smoking. Regular physical activity and social contact showed little to no independent effect on cognitive decline in this study.
Discussion & Takeaways
These findings have important implications for both individuals and public health efforts. The researchers suggest that quitting smoking - or never starting - may be the most important step people can take to maintain cognitive function as they age. This is particularly relevant given the lengthy preclinical period of conditions like Alzheimer's disease, where brain changes can occur decades before symptoms appear.
However, the researchers caution against completely disregarding other healthy behaviors. While this study didn't find strong independent effects of physical activity and social contact on cognitive decline, these factors are known to have numerous other health benefits. Additionally, for those who smoke and find it difficult to quit, adopting other healthy habits may help to some extent in mitigating cognitive decline.
