Seniors who may require home care may be able to limit the progression of lessened cognitive ability if they, along with their assistants' help, follow healthy lifestyle choices that help maintain good levels of vitamin D.
The vitamin is present in oily fish which often contain omega-3 fatty acids, and multivitamins which may help improve nutrition.
Levels may also be improved by outside activity.
At eight centers throughout Europe, researchers followed the cases of 3,000 men ages 40 to 79 to see how they responded to tests measuring their attention and ability to process information.
Scientists at University of Manchester found that those with higher levels of the vitamin were able to perform the tasks more easily than participants with lower vitamin levels, a result they say is stronger than prior "inconsistent" studies because of the large sample size.
"Interestingly, the association between increased vitamin D and faster information processing was more significant in men aged over 60 years," said lead author Dr David Lee, adding that there is a "potential benefit for minimizing ageing-related declines in cognitive performance."