Researchers from the Peninsula Medical School, the University of Cambridge and the University of Michigan have carried out the first international comparison of cognitive function in nationally representative samples of older adults in the US and England and discovered that US seniors performed significantly better that their English counterparts.
The finding is surprising because older people in the US are known to suffer more from cardiovascular risk factors and diseases, which are generally associated with more cognitive decline and poorer mental function.
The study compared 8,299 Americans with 5,276 British seniors aged 65 and older. The same cognitive tests were administered to the two groups in the same year. The US advantage in 'brain health' was greatest for those aged 85 and older. On a population level, the overall difference in cognitive performance between the two countries was quite large and amounted to a decade of ageing – the cognitive performance of 75-year-olds in the US was as good, on average, as that of 65-year-olds in England.
Data from the US population came from the Health and Retirement Study, conducted by the University of Michigan Institute for Social Research and funded by the National Institute on Aging. Data on the UK study were from the English Longitudinal Study of Ageing. Both are nationally representative, population-based studies designed to facilitate direct comparisons of health, wealth and well-being among older men and women.
Participating individuals in both countries took tests of immediate and delayed recall of 10 common nouns including hotel, river, tree, skin, gold, village, baby and table. They heard the words spoken and were asked to repeat as many as possible immediately. Then they completed other survey questions and five minutes later, were asked to repeat as many of the words as possible. During the interview participants were also asked what day, date, month and year it was. Taken together, their answers (10 points for immediate recall, 10 for delayed recall and four for orientation) made up a 24-point scale of cognitive function.
The researchers compared scores stratified by age, gender, and education as well as country. The mean score for the combined cognitive scale was 12.5 (out of 24) for the youngest group of English adults (ages 65-74) and 8.3 for the oldest group (age 85 and older). The mean scores for the youngest and oldest groups in the U.S. were 13.8 and 10.1, respectively.
The research team also examined data on participant health conditions, risk factors, and treatments for stroke, diabetes, heart disease, hypertension, lung disease, and cancer. They also collected data on recent symptoms of depression, and on smoking status, alcohol consumption, and limitations in performing common activities of daily living, including dressing, bathing, taking medications, and managing money.
U.S. adults reported significantly lower levels of depressive symptoms than English adults, and this may have accounted for some of the U.S. advantage in 'brain health' since depression is linked with worse cognitive function. The research team also found significant differences in alcohol consumption between the U.S. and English seniors. More than 50 percent of U.S. seniors reported no alcohol use, compared to only 15.5 percent of English seniors. Previous research has shown that moderate alcohol consumption, compared to abstinence, is linked with better cognition among those aged 50 and over.
U.S. adults reported a higher prevalence of hypertension, yet they also were more likely to be taking medications to treat the condition. A number of studies have shown a link between untreated hypertension and an increased risk for cognitive impairment.
Two researchers from the Peninsula Medical School worked on the study, Dr Iain Lang and Dr David Llewellyn. Dr Iain Lang commented: "While we in England may not like the results of this study, there are important lessons to be gleaned regarding the differences in lifestyle and the treatment of cardiovascular diseases between the US and England. Given the good results achieved by the American oldest-old, we can hypothesise that the more aggressive diagnosis and treatment of hypertension and possibly other cardiovascular risks that occurs in the US, may lead to less cognitive decline. US citizens tend to retire later than those in England, and this too can have an effect on cognitive performance – there may be a connection between early retirement and the early onset of cognitive decline."
Dr David Llewellyn added: "It is possible that the results of this study could lead to other research designed to improve cognitive performance for older people in England. Certainly, with the population of the world ageing at a rapid rate future cross-national studies regarding medical and social factors and ageing can only make significant contributions to the quality and delivery of public health – not least in providing possible savings for health and social care providers such as the NHS."
Journal
BMC Geriatrics