LONDON (Reuters) - British and Norwegian scientists believe that taking a simple supplement of folic acid and vitamin B12 could help prevent or delay the onset of Alzheimer`s disease, they said on Tuesday. But the researchers at the Universities of Oxford in England and Bergen in Norway called for further research and stressed that so far their study has revealed only an association, not a direct cause and effect between diet and the debilitating brain disease. "These findings are important because they provide a testable hypothesis that it may be possible to prevent or delay the progression of Alzheimer's disease in a proportion of potential sufferers," Professor David Smith, chairman of the department of pharmacology at Oxford, said in a statement. "However, testing this hypothesis will require long and costly trials," he added. Smith and his colleagues studied 76 Alzheimer`s patients who took part in the Oxford Project to Investigate Memory and Ageing (OPTIMA). The researchers found that patients with Alzheimer's had moderately elevated blood levels of the amino acid homocysteine and lower blood levels of folate and vitamin B12, which controls homocysteine, compared to 108 healthy people of a similar age. A moderate rise of homocysteine in the blood is also a known risk for heart disease and stroke. The discovery opens the way for an accurate blood test to identify people most at risk of the disease which is the main cause of senile dementia. Alzheimer`s affects tens of millions of people and although there is no cure, drugs can reduce some of its effects.