I know a great deal about aging but this study surprised even me.

They are called “the oldest old ‘ – those who are people age 90 and above, and they are the fastest-growing segment of the U.S. population. Yet very little is known about the oldest old, since until recently, there were so few of them. So what determines which of us will make it past age 90? What kind of shape will we be in if we do? And what can we do now to up our odds? Finding out is the goal of a groundbreaking research study known as “90+.”

Dementia, including that most dreaded form, Alzheimer’s disease, is a looming threat, and a primary focus of the 90+ study. Participants are asked to donate their brains to the study after they die, so researchers can compare what they saw in life to the secrets buried deep within. And the picture isn’t always matching up, bringing new discoveries and new questions about what may actually be causing dementia in the “oldest old” and what we may be able to do about it.

What’s amazing is they’re finding that 40 percent of the time in people over 90 — what doctors would think is Alzheimer’s — isn’t. Researchers found something else — something the 90+ study is finding quite a bit — evidence of tiny, microscopic strokes called micro infarcts.

Also in the study: No surprise – smokers died earlier than non-smokers. And what about exercise? The study recommends 45 minutes a day of moderate exercise which doesn’t have to be completed at one time. It could be, for example, 15 minutes of walking and then later in the day 30 minutes of gardening.

A few more tid bits: Vitamins make no difference to life expectancy and up to two drinks a day led to a 10-15 percent reduced risk of death compared to non-drinkers.