A lack of folic acid may lead to a threefold increased risk of developing dementia in old age, finds a new study.

South Korean researchers at the Chonnam National University Medical School in Kwanjiu observed 518 people over a 2.4-year period between 2001 and 2003 to see if they developed dementia. They were all 65 and over.

The study participants had their blood tested at the beginning of the study and throughout, a test that assessed levels of folic acid, vitamin B12 and a chemical called homocysteine. When first tested, one in five of the participants had high levels of homocysteine, 17 per cent had low levels of vitamin B12 and 3.5 per cent had lower levels of folic acid.

In those people who had high levels of folic acid, levels of homocysteine, which has been linked to increased cardiovascular risk, were lower and vitamin B12 levels were higher.

During the two-year period, 45 people were diagnosed with dementia, 30 of them specifically with Alzheimer's disease, seven with vascular dementia and four with other forms of dementia.

Those participants who had been low in folic acid at the start of the study were 3½ times more likely to develop the condition.

The researchers theorize that shifting levels of micronutrients in the body could be responsible for the onset of dementia, in the same way they lead to weight loss and low-blood pressure. But they also believe that a reverse conclusion could be made, namely that the neurodegenerative process associated with dementia could also lead to decreased folic acid in the bloodstream.

The authors suggest further research to clarify this relationship.

Regardless, they suggest that folic acid supplementation could be helpful. "There may be good arguments for focusing interventions for the prevention of dementia on nutritionally deficient frail populations," reads the study.

The findings are published online in the Journal of Neurology, Neurosurgery and Psychiatry.