Q. At what age does my brain no longer grow new cells (neurons)? Can I delay senility or improve cognition? What's DHEA?

A. You have almost all the neurons you will ever have at birth, but your brain continues to grow for several years because its glial cells continue to multiply. Glia promotes brain function and insulates neurons with myelin. And neurons continue to make new connections after birth.

The hormone DHEA declines with age and was believed to be neuroprotective and anti-aging. To know if something like DHEA really works, you need to compare it to a placebo, or fake pill, and do a randomized study, otherwise you won't know if it's the power of suggestion or other medical or social issues that really improved memory or reduced strokes.

The highly regarded Cochrane Database group studies everything from statin drugs to ear wax using only the most accurate, randomized studies. On Oct. 18, it found that DHEA did nothing for memory or thinking, and may even worsen visual memory.

The very next day, the New England Journal of Medicine reported on whether DHEA could delay aging. They even added testosterone in men with low testosterone levels, but found that after two years, neither DHEA nor testosterone improved any aspect of aging, such as physical performance, body composition, bone strength, glucose tolerance or quality of life. And because DHEA is not FDA-approved, its purity and safety are unknown.

The Cochrane Database group also found that in those with senility, thiamine, lecithin, selegiline, ibuprofen and alpha lipoic acid did not help. There was some evidence that ginkgo biloba helped, though more recent studies were conflicting.

In healthy folks, this group found that omega-3 fatty acids (fish oil), folic acid, and vitamin B6 with or without vitamin B12 did not improve thinking or prevent senility. And in the only randomized study of cognition or senility that I could find on vitamin C, published in Neurology on Nov 9, 2004, adults who took vitamin C 500 mg, vitamin E 400 IU and beta carotene at 15 mg a day did not have better cognitive function seven years later.

A study reported in the April 14, 2005, New England Journal of Medicine also found that vitamin E did not delay senility. In fact, an analysis of multiple randomized studies found that vitamin E above 150 International Units a day may actually increase death rates. Kaiser no longer sells vitamin E at doses above 100 IU.

So forget vitamins. To delay senility, get regular exercise, eat more fruits and veggies, quit smoking, watch your weight and keep your alcohol (even red wine) intake to fewer than one or two drinks a day.

Dr. Landis Lum is a family practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i's John A. Burns School of Medicine. Send questions to Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.