Olive oil is one of the staples of the Mediterranean diet, which is high in vegetables, grains and fish.
Eating a diet rich in fish and vegetables, while low in meat and dairy, lowers an older person's risk of developing mild mental impairment and Alzheimer's disease, a study showed.
Those who adhered most closely to the Mediterranean diet had a 28 percent lower risk of developing mild cognitive impairment, which is a precursor to Alzheimer's disease in many people, than those who didn't, research in the February issue of Archives of Neurology found.
The benefit was larger for those who already had cognitive impairment. People with the impairment who followed the diet closely had a 48 percent lower probability of developing Alzheimer's disease than those who didn't eat similar food, according to the study, which is among the first to examine the effect of the Mediterranean diet on the risk of this mental decline.
"It's another piece of evidence that should reinforce healthy diet behavior," said lead author Nikolaos Scarmeas, an assistant professor of neurology at Columbia University Medical Center in New York. With this study, people "have an additional reason to follow a healthy diet. It may not only help them from vascular risk factors, but it may also be helpful for their brain function as well."
About 5 million Americans ages 65 and older have Alzheimer's, and the number may triple by 2050, according to the Alzheimer's Association. Mild cognitive impairment is the stage between the normal mental decline seen with aging and more serious problems caused by Alzheimer's, according to the Mayo Clinic. Not all people with mild cognitive impairment go on to develop Alzheimer's.
Researchers in the study looked at 1,393 people with no cognitive problems and 482 people with mild cognitive impairment. Those in the study were asked to complete a food questionnaire. They were then divided into three groups based on how closely their eating habits matched the Mediterranean diet. The average age in the study was about 77.
Among those who started the study with mild cognitive impairment, 106 developed Alzheimer's disease over about 4.3 years of follow-up. Those in the group that stuck most closely to the Mediterranean diet showed a 48 percent lower risk for developing Alzheimer's.
Scarmeas cited many reasons why the Mediterranean diet may lower the risk of Alzheimer's and mild cognitive impairment. The diet has been shown to help lower blood pressure and cholesterol, and it reduces inflammation in the body, all of which may play a role in developing either mental condition, he said.