People who reached middle age without high blood pressure, type 2 diabetes or a smoking habit went on to live almost 13 more years free of dementia than people who had all three. That is the finding of an analysis of 12,409 Americans followed for a quarter of a century, published on 5 August in Neurology Open Access.
The figures are concrete. Participants with none of the three risk factors averaged 30.1 further years without dementia. One risk factor cut that to 26.3 years, two to 21 years, and all three to just over 17. Those carrying all three were 2.69 times as likely to develop dementia.
Researchers at NYU Langone Health drew on the Atherosclerosis Risk in Communities study, which began in the 1980s and tracked participants into old age. The 12,409 people analysed averaged 56 years old and were free of dementia when their risk factors were measured. Over a median follow-up of 26.3 years, 3,008 developed dementia and 5,238 died without it.
Counting years rather than risk
The unusual part is what the researchers chose to measure. Most dementia studies report the chance of developing the disease. This one reports how long people live without it.
"Rather than focusing only on the chances of developing dementia, this study asks a question that matters to people: how long can we expect to live free from dementia?" said Jacqui Hanley, head of research funding at Alzheimer's Research UK, who was not involved in the work.
Two gaps run through the results. Women lived longer without dementia than men whatever their risk profile, and white participants had more dementia-free years than Black participants. The authors point to unequal access to care and to differences in how the risk factors are treated.
The wider stakes are large. The number of people living with dementia worldwide is forecast to nearly triple to 153 million by 2050. Earlier research has estimated that addressing 14 modifiable risk factors across a lifetime could prevent or delay 45 percent of cases.
"Hopefully, these results will encourage people to stop smoking and watch their vascular health closely from age 45 on," said Josef Coresh, senior investigator and director of the Optimal Aging Institute at NYU Langone.
One caution belongs with the headline number. This was an observational study, and it cannot promise any individual 13 extra years. "The figure compares people with none of the three risk factors with those who had all three, and dementia-free survival reflects both the timing of dementia and overall longevity," the internist Dung Trinh of the Healthy Brain Clinic in Irvine, California, who was not involved in the study, told Medical News Today. People who avoid these three conditions also live longer, which is part of what the number captures.