Dementia and Exercise

I ran across this article this a.m. and I was left scratching my head.

Researchers assessed the health of more than 45,000 men and nearly 15,000 women, ages 20 to 88 years, in the United States and grouped them into one of three fitness categories -- low, middle or high.

After an average follow-up of 17 years, about 4,050 participants died. Of those deaths, 164 were attributed to dementia (72 vascular dementia and 92 Alzheimer's disease). Of those 164 deaths, 123 of the people were in the low-fitness group, 23 were in the middle-fitness group, and 18 were in the high-fitness group. http://www.nbc12.com/story/16924067/exercise-a-defense-against-dementia-study

As I read the above, I could only come away with the following 2 questions and one observation:

• Question 1:  Of the 45,000  participants, how many of them fell into each of the fitness categories?
• Question 2: Over the 17 years, long was their fitness level maintained.  Fit at 20 is not the same as unfit at 40, 50,60....
•  Observation:  Is the incidence of dementia among the fitness groups any different?  Or...Is the incidence of dementia only marginally different?  75% of the deaths were in low fitness, but that leaves 25% of the deaths in the middle to high fitness levels.  I'm simply curious as to how the middle/high group was represented in the original sample (subject to the above two questions).  
• Okay...I have another question...do we even have a statistically significant sample of N deaths from dementia to draw any conclusions.

The story is one of three things:  poor writing or poor science, or my own cognitive issues.

But having said that....we all know the benefits of keeping physically fit...dementia is a small malady compared with the chronic diseases that claim so many more lives.