SAN FRANCISCO, Jan. 21 (Xinhua) -- A U.S-led international team of scientists has found that cognitive ability in early adulthood plays a key role in one's mental capacity later in life, said a study published Monday.

The scientists, led by researchers from the School of Medicine at the University of California San Diego (UCSD), are trying to figure out the relationship between early adult general cognitive ability (GCA) and cognitive capabilities of people such as education and intellectual activities when they are in their advanced years of life.

They focused the study on the effects of GCA, or a diverse set of skills involved in thinking, such as reasoning, memory and perception, in people's early adulthood as they examined more than 1,000 veterans of the Vietnam War era, who are now in their mid-50s to mid-60s.

The scientists, who had their research results published Monday in the U.S. journal Proceedings of the National Academy of Sciences (PNAS), found that the cognitive capabilities of the veterans, 80 percent of whom had no combat experience, were more associated with their cognitive performance as was demonstrated in a qualification test at the age of 20.

The GCA at age 20 accounted for only about 10 percent of the variance in assessments of each of the seven cognitive domains including memory, abstract reasoning and verbal fluency, said the study.

"The findings suggest that the impact of education, occupational complexity and engagement in cognitive activities on later life cognitive function ... are largely downstream effects of young adult intellectual capacity," said the study's first author William Kremen, a professor of psychiatry at the UCSD School of Medicine.

The scientists believed that the role of education in increasing GCA took place primarily during childhood and adolescence when the brain's development continued to progress substantially.

They suggested that having better-quality childhood and adolescent education could help prevent cognitive capabilities from declining when people grow older.