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Exercise topped the Alzheimer's prevention list
The assignment
In 2014, the physician gave his analyst, Dan Pelletier, a project: pull together all the mechanistic and clinical trial data on Alzheimer's prevention, and map every input and the way it offers protection. The work took nine months to a year, and the presentation that came back put exercise first.
The pushback
The physician did not believe it. He suspected a drug had been missed, or that EPA and DHA must have a bigger effect, and pushed back for about six months. The analyst's answer was that exercise touches every aspect of the brain: BDNF, vascular endothelium, glucose disposal, and insulin signaling. After a neurologist who works on Alzheimer's prevention, Richard Isaacson, was brought in, the work became a paper.
The size of the effect
The biggest gain comes at the start. Going from completely sedentary to 15 MET hours per week brings probably a 50% reduction in risk. A MET is a metabolic equivalent, about one at rest and about five for a really brisk walk, so 15 MET hours equals three one-hour brisk walks. The physician suspects the true figure is somewhat lower and that more exercise holds more upside than studies can capture.
How does exercise protect the brain?
Exercise raises levels of brain-derived neurotrophic factor, a protein that supports the survival and growth of neurons. In a 2011 randomized trial in PNAS led by Kirk Erickson, 120 older adults who walked for a year showed about a 2 percent increase in the volume of the hippocampus, a region central to memory. The control group's hippocampus shrank over the same year. Gains in volume tracked with higher BDNF levels in the blood.
Why does the first activity gain count most?
Large studies find the steepest drop in mortality at the lowest levels of activity. A 2015 analysis in JAMA Internal Medicine by Hannah Arem and colleagues pooled six cohorts with more than 660,000 adults. Those who did some activity but less than the recommended minimum already had roughly 20 percent lower risk of death than those who did none, and benefits continued to rise at a flatter slope with more activity.
Where did the MET unit come from?
The MET was built around resting oxygen consumption, which physiologists standardized at about 3.5 milliliters of oxygen per kilogram of body weight per minute. Multiples of that figure let researchers compare different activities on one scale. Barbara Ainsworth and colleagues published the first Compendium of Physical Activities in 1993, assigning MET values to hundreds of activities. The compendium has been updated several times since.
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