Jobs that are mentally stimulation could lead to a sharper brain in retirement.

People whose jobs require "problem solving, planning and information analysis" are more likely to have a clearer brain later in life, HealthDay reported.

"People who were engaged in work characterized as mentally challenging scored better on a measure of cognitive [thinking] ability, both before and after retirement," Gwen Fisher, an assistant professor of psychology at Colorado State University, told HealthDay.

Professions that encourage mental clarity include "lawyers, financial analysts, teachers and doctors," as well as project managers who must keep track of multiple assignments, HealthDay reported.

Jobs that require repetitive actions, such as working on an assembly line, can leave one mentally dull later in life.

The researchers looked at 4,200 patients who had a minimum age of 51. The subjects were interviews every two years analyzing data, the subjects were interviewed on their jobs-  "developing objectives and strategies, making decisions, solving problems, evaluating information and thinking creatively. The survey also assessed memory and reasoning skills," HealthDay reported.

The team found those who had more mentally stimulating jobs tended to have better memories after retirement.  The mental differences were not extremely significant directly after retirement, but 15 years later the gap between the two groups grew larger.

According to the study people who had mentally stimulating jobs score about 50 percent better on mental assessments than those who had not.

"[The finding] gels really nicely with other things we've seen where midlife is the point at which people really need to pay attention to their brain health," Keith Fargo, director of scientific programs and outreach for the Alzheimer's Association told HealthDay.

The researchers believe the mental stimulation gained from a challenging job could help one preserve more neurons over the course of their lives.  It could also be consistent with the idea of "use it or lose it."

"Much like muscles on our body, if you use the brain you strengthen it, and if you don't, it can atrophy," Fisher said.