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Seniors with low levels of the B vitamin folate have more than triple the risk of developing Alzheimer's disease and other forms of dementia, according to the new research.

But what remains unclear is whether the lack of folate circulating in the blood contributes to the onset of dementia or is a result of the physical changes related to memory loss.

Jin-Sang Yoon, a psychiatric researcher at Chonnam National University Medical School in Kwangju, South Korea, and lead author of the research, said that, regardless, the folate levels of the elderly provide valuable information and should be monitored.

"Attention needs to be paid to the nutritional status of people with dementia from the time of diagnosis onwards, regardless of whether this is a cause or effect of the condition."

The study, published in today's edition of the Journal of Neurology, Neurosurgery and Psychiatry, involved 518 people over the age of 65, who were tracked over a period of two years. All the participants live in South Korea.

During that period, 45 of them developed dementia - principally Alzheimer's disease, but also vascular dementia.

Researchers tested the blood levels of all participants for folate, vitamin B12 and the amino acid homocysteine.

At the start of the two-year period, 20 per cent of participants had high levels of homocysteine, while 17 per cent had low vitamin B12 levels and 3.5 per cent were folate deficient.

The higher the levels of folate to begin with, the higher were vitamin B12 levels, and the lower those of homocysteine.

The seniors with low folate levels at the outset of the study were 3.2 times more likely to develop dementia; those with low levels of vitamin B12 had a much lower risk, about 60 per cent.

A number of studies have shown that high levels of homocysteine - a substance that can make arteries stiffen and clog - translate into higher rates of heart disease and dementia.

Folate, or vitamin B9, is found in leafy green vegetables such as spinach, broccoli and asparagus, and in legumes such as lentils and kidney beans, and in citrus fruits. It is also well established that folate and B12 lower homocysteine.

What remains in question, however, is whether bolstering intake of B vitamins - for example with folic acid and B12 supplements - can actually prevent or slow the onset of dementia.

The new research does not directly answer that question, but it does demonstrate quite clearly that a drop in folate levels is closely associated with the onset of dementia.

Dr. Yoon and his team cautioned that when people begin to suffer from dementia, one of the first effects is dietary changes - the poor eating habits could explain the drops in folate and B12 levels. People with dementia also suffer weight loss and a drop in blood pressure.

Dr. Yoon said the "relationship between weight loss and micronutrient concentrations is potentially complex," but the new research suggests that it may be related to poor diet.

The researcher said that paying more attention to the "nutritionally deficient frail population" is probably a good strategy for delaying the onset of dementia.

Since 1998, Canada has fortified staples such as flour, pasta and cornmeal with folic acid (the synthetic version of folate). The result has been a dramatic reduction in birth defects such as spina bifida and in some forms of childhood cancer such as neuroblastoma.

Some researchers also believed that fortification would also results in a drop in cardiovascular deaths and in dementia, but that has not panned out.

South Korea, where the study was conducted, does not fortify foods with folic acid.