Experts in human nutrition believe that eating eggs may help to prevent the onset of dementia in the ageing population.Scientists in the United States are setting up a research study to examine the effect of egg consumption on cognitive function in people over 50 years old. And the research team, which is based at the Human Nutrition Research Centre on Ageing at Tufts University near Boston in the United States, appears confident that eating eggs will be shown to be beneficial. "The investigators hypothesise that there will be a significant increase in cognitive function measures in older adults," the team says in a submission outlining its proposals. The proposals are detailed at clinicaltrials.gov, a service run by the United States National Institutes of Health.The team's research will focus on two nutrients called lutein and zeaxanthin, which are found in egg yolk. Lutein and zeaxanthin are known as carotenoids and they are said to filter harmful high energy blue wavelengths of light and act as antioxidants in the eye, helping protect and maintain healthy cells. It is believed that they prevent macular degeneration, cataracts and age related blindness. The doctor heading up the new study at Tufts University is Elizabeth J Johnson, whose previous work includes research into carotenoids, lutein and zeaxanthin. In a 2008 study for the American Society for Clinical Nutrition called 'The influence of supplemental lutein and docosahexaenoic acid on serum, lipoproteins, and macular pigmentation,' she found that lutein and docosahexaenoic acid "may aid in prevention of age related macular degeneration." Her work has been repeatedly cited by other researchers looking into ways of preventing age related macular degeneration and Elizabeth Johnson, herself, has conducted numerous other studies on the effects of carotenoids, lutein and zeaxanthin on ageing people. For the new Tufts University study, Elizabeth Johnson and her team say that their previous work leads them to believe that the consumption of eggs will be shown to help cognitive function. "Our studies have shown that egg interventions can significantly increase serum lutein concentrations in older adults," they say in the study proposals published by the United States National Institutes of Health. "Based on the sum of our findings, the next logical step will be to investigate the ability of lutein and zeaxanthin contained in eggs to influence cognitive function in older adults. The investigators hypothesize that there will be a significant increase in cognitive function measures in older adults provided with meals containing two eggs a day at the end of six months, while no significant improvements will be observed in older adults given daily meals containing egg substitute."The planned study will comprise a placebo controlled trial lasting six months in which volunteers will receive either two eggs or four ounces of egg substitute each day. Those taking part in the trial will all be more than 50 years old. "Cognitive impairment is also a major risk factor for development of dementia later in life," said the researchers in the National Institutes of Health published proposals. "Findings from our studies suggest that the carotenoids, lutein and zeaxanthin may be important in cognitive function in the elderly. The investigators have previously reported eggs to be a highly bioavailable source of lutein and zeaxanthin. Our study evaluates long term egg intervention as a treatment strategy for age related cognitive impairment, which could possibly prevent the onset of dementia. The investigators have also shown that lutein supplementation significantly improved verbal fluency scores in healthy older women."According to the Macular Society, lutein and zeaxanthin can only be obtained by the human body through the diet. They can be found in vegetables, particularly dark green leafy vegetables, such as kale and spinach, as well as corn and corn products, but they are also present in high levels in eggs, and the lutein and zeaxanthin in eggs are more easily absorbed by the body than those in vegetables because of the fats they contain. A study carried out in 2006 found that eating just one egg each day over a period of five weeks significantly increased levels of lutein and zeaxanthin in older people.According to the Egg Nutrition Centre in the United States, there is preliminary evidence that lutein and zeaxanthin may also protect against different types of cancer, coronary heart disease and stroke, as well as reducing the risk of cataracts and age-related macular degeneration. For the Tufts University study, researchers will be recruiting both men and women to take part in the trial. The scientists say that all participants will be screened to "meet cognitive and functional criteria." Participants will be pre-screened by telephone and those who appear to meet the team's criteria will undergo further screening. All the volunteers will undergo tests for memory, reasoning, verbal fluency and attention span to determine what impact egg consumption may have on cognitive function.