Middle-aged women with high levels of homocysteine in their bloodstream could be at more risk of developing Alzheimer's. Homocysteine is an amino acid that is important for the body's metabolism but too much of it can damage blood vessels and increase the risk of blood clots. Swedish scientists started following 1,500 women aged between 38 and 60 at the end of the 1960s. They took blood samples and can now compare the levels of different substances in people's blood with who went on to develop Alzheimer's later. The study - a Ph.D. thesis at the University of Gothenburg - found that those women with the highest levels of homocysteine had twice the risk of developing Alzheimer's as those with the lowest levels.