You may recall that in 2008, the Ginkgo Evaluation of Memory study, or GEM, concluded that ginkgo was ineffective in reducing the incidence or progression of Alzheimer's disease and other types of dementia. However, given previous studies suggesting that ginkgo might be useful for people with milder cognitive impairment, the GEM group also decided to look at the effect of ginkgo on cognitive decline in normal older adults or adults with only mild cognitive impairment.

The resulting study, published last month in the Journal of the American Medical Association, suggests that ginkgo is not helpful in preventing cognitive decline in older adults. In this study, more than 3,000 adults with normal cognition or mild cognitive impairment, ages 72 to 96, were randomized to receive either ginkgo (120 mg, twice daily) or a placebo for about six years.

At the end of the study, the researchers found no differences between the ginkgo and placebo groups in their assessment of memory, attention and language, or rate of decline in cognitive impairment. Age, gender, race and education did not seem to have any impact on the outcomes.

The authors concluded that ginkgo biloba taken in that amount was ineffective in preventing cognitive decline in older adults with either normal cognitive function or mild cognitive impairment.

Ginkgo has intrigued researchers as a brain supplement because it seems to have a positive effect on blood vessels in the brain -- it dilates them, thins the blood a bit (thought to enhance circulation) and functions as an antioxidant.

In addition, animal studies have suggested it may inhibit amyloid protein in the brain, which is a cause of Alzheimer's disease. However, the data have been inconsistent about positive effects in humans, and this most recent study is not encouraging.

In addition, the Cochrane Library, an international nonprofit organization that reviews the efficacy of health care interventions, reviewed 36 research studies of ginkgo in 2009 and concluded that while ginkgo biloba appears to be safe and without significant side effects, it does not seem to reduce the risk of cognitive decline or dementia.

That said, several other lifestyle choices and supplements are showing some promise:

—Fish: Observational studies show a link between a high intake of fish and a reduced risk of Alzheimer's disease as well as a reduced risk of cognitive decline in non-demented individuals.

—Vitamin D: A 2009 British study showed that people with the lowest levels of vitamin D in their blood were more than twice as likely to be cognitively impaired than those with the highest levels.

—Vitamin E: It might help delay the progression of Alzheimer's, but some data suggest vitamin E may actually increase mortality. Stay tuned.

—Other nutrients: Adequate intake of vitamin B3 (niacin), vitamin B12 and iron are all associated with improved cognition.

—Turmeric: An observational study from 2006 showed that healthy people ages 60-93 who ate curry (turmeric) at least once a month scored better on cognitive tests than people who rarely ate curry.

—Diet: People who follow the Mediterranean diet (high in plant food, low in animal food) seem to have a lower risk of Alzheimer's.

—Stress: Chronic stress impairs the growth of new brain cells and seems to lead to changes in memory.

Several other supplements look promising for Alzheimer's disease, including huperzine A, phosphatidylserine, acetyl-L-carnitine and vinpocetine, though long-term effectiveness and safety are still unknown. Also, many of these supplements can interact with other medicines, including prescription drugs used for Alzheimer's as well as blood thinners, so talk to your doctor before trying any.

And of course, do everything you can to prevent dementia in the first place: Stay active, stay with a healthy diet and healthy weight, and stay engaged in your community. Your aging destiny is largely in your hands.