Vitamin B12: The Oxford Project to Investigate Memory and Aging (OXPRIMA) found that adults over 55 years of age who had low B12 levels also had four times the average risk of dementia. As they age, many people lose their ability to absorb B12 from the foods they eat. Some vegans also have B12 deficiency because all sources of the vitamin are animal products — fish, poultry, dairy products, and yeast, for example. Have your doctor check your B12 levels as part of a routine blood panel. If your levels are low due to poor absorption, vitamin supplements won’t do you any good, but a monthly injection of B12 will.

Folate: In the OXPRIMA study, low folate levels correlated with triple the average risk of Alzheimer’s. Good sources of folate are leafy green vegetables, dried legumes, whole grains, and citrus.

Iron: A deficiency in iron, which is crucial for the maintenance of brain cells, is especially common among women. It’s also common among adolescent girls. Iron deficiency affects thinking skills in general, and even mild deficiency has been found to have a particularly strong impact on mathematical reasoning skills. One theory holds that iron deficiency may be partly responsible for boys’ superiority in math skills from adolescence on. Good sources: meat, dark leafy green vegetables, whole grains, beetroot, raisins.

Antioxidants: Highly reactive hydrogen, oxygen, and iron molecules called free radicals can kill brain cells by punching holes in their protective membrane. Some of the best-known forms of protection against free radicals are antioxidants, also known as free radical scavengers. Vitamins C and E are both antioxidants. Good sources of vitamin E are vegetable oils, nuts, and leafy green vegetables. Good sources of vitamin C are fruits and vegetables, especially: citrus, kiwifruit, mangoes, guavas, persimmons, rose hips, tomatoes.

Extracts from the Ginkgo biloba tree have been the subject of trials in Europe and North America that produced claims of beneficial effects on memory and alertness. The exact mechanism by which ginkgo might have any benefit is still a subject of investigation. Some have pointed to anti-clotting and antioxidant properties, and its ability to boost blood supply to the brain. Like vitamin E, it is low-risk and non-invasive, so it is sometimes recommended to those with mild cognitive impairment or memory complaints.