Experts from the Institute of Psychiatry at King's College London analyzed data from more than 1,300 people with dementia. They considered factors including education, employment and retirement.
Researchers found that people who retired later were able to avoid the mind-robbing Alzheimer's disease longer than people who retired earlier.
Each extra year of work was associated with approximately a six-week delay in the onset of dementia.
The study was published in the International Journal of Geriatric Psychiatry and was paid for by the Alzheimer's Research Trust and Britain's Medical Research Council.
"The intellectual stimulation that older people gain from the workplace may prevent a decline in mental abilities, thus keeping people above the threshold for dementia for longer," said Simon Lovestone, one of the paper's co-authors, in a press statement.
But Lovestone acknowledged that doctors still did not fully understand how to delay or prevent dementia.
Previous studies have suggested more education may lower dementia risk.
Other experts said more research was needed to confirm the study's findings.
"There could be a number of reasons why later retirement in men is linked with later onset of dementia," said Suzanne Sorensen, head of research at the Alzheimer's Society. Sorensen was not linked to the study.
She said men who retired early might have done so because of other health problems like high blood pressure or diabetes, which increases dementia risk.
"It could also be that working helps keep your mind and body active, which may reduce risk of dementia," she said.
Alzheimer's disease is the most common cause of dementia and accounts for nearly 60 percent of all cases. Dementia affects 1 in 20 people over the age of 65.
According to Alzheimer's Disease International, there are an estimated 30 million people worldwide with dementia.
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