Researchers believe the study reinforces the link between B vitamins and the condition. The Alzheimer’s Research Trust called for a large-scale trial to conclusively prove the association.
Many previous studies had linked the amino acid homocysteine, which is associated with vitamin B12, to the development of cardio/cerebrovascular diseases.
To examine whether there was also a link with Alzheimer’s, researchers analysed blood samples of 271 Finnish people aged 65-79 without dementia.
Samples were tested for homocysteine and the active element of vitamin B12, holotranscobalamin.
Researchers saw that elevated homocysteine levels increased the risk of Alzheimer’s. But they also found a rise in holotranscobalamin levels reduced risk.
Researchers said further work may allow vitamin B12 to be used as a marker to identify patients at increased risk.
Professor Helga Refsum of the Alzheimer’s Research Trust said: ‘This study adds further evidence that low vitamin B12 status is associated with Alzheimer's, and it is probably the first to link the active component of the vitamin to the incidence of dementia.’
Rebecca Wood, chief executive of the Alzheimer’s Research Trust, said: ‘Discussion continues around how much promise B vitamins hold in protecting us from dementia, a debate that can only be put to bed by a comprehensive large scale trial.’
But she warned against patients ‘stocking the cupboard’ with vitamin B supplements, saying it was too early to be sure of the benefits.