Researchers took into account study participants' education, employment and retirement.
Researchers found that each year spent working roughly translates into a six-week delay in the onset of dementia.
One of the study co-authors said the "intellectual stimulation" from the workplace helps to keep your brain synapses firing.
Other experts point out that people who retire early may have done so because of other health problems, like high blood pressure or diabetes, which increase their risk for dementia.
The study was published in the International Journal of Geriatric Psychiatry.
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.