Although long-term placebo-controlled studies are rarely available for dietary supplements, research has shown cognitive benefits for several, including:

Antioxidants. In the late 1990s, a large-scale study showed that 2,000 IU of daily vitamin E slowed the progression of Alzheimer’s disease. However, later research raised concerns about side effects for doses greater than 400 IU. Initial studies with antioxidant pomegranate juice suggest its benefits in people with mild memory changes.

Vitamin B. The B vitamin folate may protect older adults from strokes. Vitamins B6, B12, and folate are involved in the breakdown of homocysteine — an amino acid building block of protein. High homocysteine blood levels increase the risk for Alzheimer’s disease. Vitamin B supplementation in patients with mild cognitive impairment slows cognitive decline and brain shrinkage compared with a placebo.

Vitamin D. Low vitamin D levels are associated with cognitive decline. A study of approximately 5,000 older women showed that those taking the recommended amount had better cognitive function than those who did not, but not all studies have replicated such benefits.

Omega-3 fats (fish oil). Omega-3s may benefit people with mild age-related memory complaints. One study showed that 2.2 grams of omega-3 taken daily for four months led to significant cognitive benefits compared with placebo. Omega-3s also improve the brain’s executive function, which translates into better planning and organizational skills.

Huperzine A. Some studies have demonstrated its effectiveness in patients with dementia or milder cognitive problems, but others show no benefits. A small investigation indicated cognitive benefits in adolescents treated for a month, but more research is needed to confirm its memory effects in older adults.

Phosphatidylserine. Several studies have shown cognitive benefits in people with age-related memory decline after three months of treatment. One study indicated that phosphatidylserine plus an omega-3 fatty acid improved memory compared with a placebo after 15 weeks of treatment.