Dementia prevention: reason enough for road tolls and public transit

I was a persistent skeptic. I didn't believe that exercise slowed the inevitable [1] onset of age related cognitive decline.

The animal models broke my resistance. Now we're exploring mechanisms (emphases mine) ...

Observations: Aerobic exercise bulks up hippocampus, improving memory in older adults

... adults aged 55 to 80 years who walked around a track for 40 minutes on three days a week for a year increased the volume of their hippocampus, the brain region that is implicated in memory and spatial reasoning. Older adults assigned to a stretching routine showed no hippocampal growth. The 120 previously sedentary older adults recruited for the study did not yet have diagnosable dementia but were experiencing typical age-related reduction of the hippocampus, according to pre-study MRIs. "We think of the atrophy of the hippocampus in later life as almost inevitable," ...

The growth of the hippocampus was modest, increasing 2.12 percent in the left hippocampus and 1.97 percent in the right hippocampus, which effectively turns back the clock one to two years in terms of volume. The stretching group, on the other hand, experienced continued reduction in pace with expected age-related losses, losing on average 1.40 percent and 1.43 percent in the volume of their left and right hippocampus, respectively...

In addition to the increased size of the hippocampus, the aerobic exercise group also tended to have a higher level of brain-derived neurotrophic factor (BDNF), a compound that is associated with having a larger hippocampus and better memory. The researchers did not see any changes in the thalamus or caudate nucleus, two other parts of the brain that are involved with spatial sense and memory, respectively. Because only the hippocampus seemed to be affected by the aerobic exercise regime, the researchers reasoned that the activity might be acting specifically on certain molecular pathways to prompt "cell proliferation or dendritic branching," they noted...

This was a randomized (non-blinded of course) therapeutic trial and it's backed up by persuasive animal model studies. I think this is real.

I would not call the effects "modest". Over one year there was a 3.4% difference in hippocampal volume between the control and experimental groups. This corresponds to a 2-4 year age gap. There is no reason to assume the groups would not continue to diverge for additional time.

This is a big enough difference that ethics panels may not approve further experimental studies of this sort. Future control groups will have to include significant exercise (I would not call 40 minutes 3 times a week modest.)

So now we have a few known ways for individuals to reduce their personal risk of cognitive disability:

1. Don't hit your head. That means no football for your kids (and, worse, maybe no hockey).
2. Exercise (without hurting your head) a lot.
3. Don't smoke, drink to excess, eat too much, etc.

We know things that don't work at all ...

1. Playing bridge, cognitive work, crosswords, etc.
2. Nutritional supplements

And we're waiting to find out if sleeping 7-8 hours a night will matter. I have a hunch sleep duration will be found to be a key to amyloid turnover ...

Insights Give Hope for New Attack on Alzheimer’s - Gina Kolata - NYTimes.com

...  Dr. Bateman was his own first subject. He then did the test on people in their 30s and 40s, as well as healthy older people and people with Alzheimer’s...

The problem in Alzheimer’s, he found, is disposal. Beta amyloid, he found, normally is disposed of extremely quickly — within eight hours, half the beta amyloid in the brain has been washed away, replaced by new beta amyloid.

With Alzheimer’s disease, Dr. Bateman discovered, beta amyloid is made at a normal rate, but it hangs around, draining at a rate that is 30 percent slower than in healthy people the same age. And healthy older people, in turn, clear the substance from their brains more slowly than healthy younger people.

... “What we think may be happening is that a clearance mechanism is broken first,” Dr. Bateman says. Slowly, as years go by, beta amyloid starts to accumulate in the brain. If that clearance can be fixed, or enhanced, the buildup might never occur...

Of course exercise helps regulate sleep as well ...

We know enough to make some policy decisions. The economic payoff to delaying cognitive disability across the US population is enormous. It's enough of a savings, for example, to justify a shift to public transit, which leads to higher levels of ambulation. A carbon tax, which makes sense in many other ways, can pay for public transit, reduce automobile use, and reduce dementia rates.