Feeling lonely increased risk for all-cause dementia by 31 percent and cognitive impairment by 15 percent. Loneliness is a common — some would even say, universal — human experience.

Diet seems to be a crucial player. In the past, several systematic reviews have found healthy diets, like the Mediterranean diet, are linked to a reduced risk of dementia. Meanwhile, the Western diet, which is high in saturated fat, sugar, and salt, seems to be a risk factor for dementia.

A study of more than 9,800 adults in their 70s showed that those with stable cholesterol levels had a "significantly lower" risk of dementia.