High intake of the vitamin niacin, particularly from food sources, may reduce the risk of Alzheimer's disease and age-related mental decline.

The study in the Journal of Neurology, Neurosurgery, and Psychiatry points out that severe niacin deficiency is known to cause dementia. However, the researchers note that it is unclear if more subtle variations in niacin intake influence the risk of mental deterioration.

"There have been no epidemiologic studies to look at the association between dietary niacin and Alzheimer's disease or cognitive decline," lead author Dr. Martha C. Morris, from the Rush Institute for Healthy Aging in Chicago, told Reuters Health.

Moreover, "animal studies and other studies have really focused on the effects of very high therapeutic dose levels of niacin," not amounts found in a standard diet.

To investigate, the researchers asked several thousand elderly people living in a Chicago community about the types and amounts of food they ate and tested their mental abilities.

The study focused on 815 randomly selected subjects who were free from Alzheimer's disease at the start of the study. After an average of nearly four years, 131 of the participants were diagnosed with Alzheimer's disease.

A high level of total niacin intake seemed to protect against both Alzheimer's disease and cognitive decline. The association was stronger for niacin intake from foods than for niacin taken in vitamin supplements.

"We were surprised to see a fairly strong association between niacin intake from foods and Alzheimer's disease," Morris said. Compared with the lowest intake, the highest intake "was linked to an 80 percent reduction in risk."

In the overall study population, high niacin intake was also linked to a reduced risk of cognitive decline.

Although the finding are provocative, Morris concluded, they will require verification before any changes to current dietary guidelines can be recommended.

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