The benefits were modest, but encouraging, indicating that the 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," confirmed Janine Walker, the lead author of the study and a researcher at Australian National University.

The researchers asked more than 700 people, aged 60 to 74 years, to take a daily dose of folic acid and vitamin B12 or fake pills that resembled the vitamins.

The vitamin dose included 400 micrograms of folic acid and 100 micrograms of vitamin B12. The participants didn't know which pills they were assigned to take.

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

Two years on, however, those who took the vitamins showed larger improvements in their scores on the memory tasks.

The difference in the improvements was small, the researchers write in their study, published in the American Journal of Clinical Nutrition.

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.