The benefits were modest but encouraging, said author Janine Walker, a researcher at Australian National University, of the study published in the American Journal of Clinical Nutrition.

"(Vitamins) may have an important role in promoting healthy ageing and mental wellbeing, as well as sustaining good cognitive functioning for longer on a community-wide scale," said Walker in an email to Reuters Health.

The researchers asked more than 700 people aged 60 to 74 years to take a daily dose of folic acid and vitamin B12, or placebo pills that resembled the vitamins. The vitamin dose included 400 micrograms of folic acid and 100 micrograms of vitamin B12, and participants didn't know which they were assigned to take.

The people taking part in the study showed signs of depression, but none had been diagnosed with clinical depression, the researchers said.

"We felt that older people with elevated depressive symptoms were an important cohort to target given evidence that late-life depression is associated with increased risk of cognitive impairment," Walker said.

After 12 months, there seemed to be no difference between the groups in how well people scored on mental tests, including memory, attention and speed.

But after two years, those who took the vitamins showed more, if modest, improvement in their scores on the memory tasks.

For instance, on a short term memory test, those who took the fake pills improved their score from about 5.2 to about 5.5 over two years. Those who took the vitamins increased their test scores from 5.16 to about 5.6.

Short term memory is used to dial a number someone has just told you, while long term memory comes into play when you try to call that number a day or week later.

It's not yet clear how taking vitamins might work to boost brain functioning, and not all studies have agreed on their benefits.

One idea is that the vitamins reduct the body's levels of a molecule called homocysteine, which is linked to cardiovascular disease and poor cognitive function. The thinking goes that lowering homocysteine could perhaps reduce the cardiovascular risk, and in turn affect mental functioning.

Joshua Miller, a professor at the University of California, Davis, said it's difficult to translate the memory improvement on the tests into real life benefits, with some people likely having larger memory improvements and others much less.

"For any given individual, there may or may not be an effect," he said.

"But on a population level, a small increase in cognitive function can have very real ramifications on the functioning of the population as a whole, and on the costs of healthcare."

Further tests are needed, including whether other groups of people, especially those older than people in the new study, would also benefit from taking vitamins, Walker said.

SOURCE: bit.ly/yyx6YW

(Reporting from New York by Kerry Grens at Reuters Health; editing by Elaine Lies)

• A Permanent Economic Emergency