Regular exercise has long been known to play a key role in keeping dementia and Alzheimer's disease at bay. In fact, it's so important it's ranked No. 1 among the "Six Pillars of Alzheimer's Prevention" by some medical sources.

The other five pillars are social engagement, healthy diet, mental stimulation, quality sleep and stress management.

Regular physical exercise can reduce your risk of developing Alzheimer’s disease by up to 50 percent, according to the Alzheimer’s Research & Prevention Foundation (ARPF). This nonprofit based in Colorado points out a person is diagnosed with Alzheimer’s every 65 seconds. Alzheimer's, which afflicts 5.4 million Americans, is now the 6th leading cause of death in the U.S. Alzheimer's leads to memory loss and difficulty in thinking, and causes up to 70 percent of all dementia cases.

ARPF emphasized that exercise can slow further deterioration in Americans that have already started to develop cognitive problems. It said exercise protects against Alzheimer’s and other types of dementia by stimulating the brain’s ability to maintain old connections, as well as make new ones.

Staying healthy through exercise will take a lot of sweat though. You should aim for at least 150 minutes of moderate intensity exercise each week. The ideal exercise plan involves a combination of cardio exercise and strength training. For beginners, a great way to start is by walking or swimming.

Moderate levels of weight and resistance training increase muscle mass and help maintain brain health. For those over 65, adding at least two strength sessions to your weekly routine could cut your risk of Alzheimer’s in half.

The Alzheimer’s Society noted that of all the lifestyle changes that have been studied, taking regular physical exercise appears to be one of the most effective strategies for reducing a person's risk of getting dementia.

Now that you know the value of regular exercise in preventing Alzheimer's, you've also got to know what exercises will be good for you.

Several studies suggested aerobic exercise, or exercise that increases one's heart rate, in middle-aged or older adults has led to improvements in thinking and memory. Aerobic exercises also seem to have reduced rates of dementia.

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Yoga is also being recommended for its ability to boost brain health. A recent analysis suggested yoga may be as effective as aerobic exercise for brain health. A study published last week in the journal Brain Plasticity suggested yoga’s effect on brain health might be as beneficial as aerobic exercise.

To reach this conclusion, the study focused on 11 studies of the relationship between yoga practice and brain health. Five of the studies engaged individuals with no background in yoga practice in one or more yoga sessions per week over a period of 10 to 24 weeks. It compared brain health at the beginning and end of the intervention.

The other studies measured brain differences between individuals who regularly practice yoga and those who don't. All the studies involved Hatha yoga, which includes body movements, meditation and breathing exercises.

"From these 11 studies, we identified some brain regions that consistently come up, and they are surprisingly not very different from what we see with exercise research," Neha Gothe, a University of Illinois kinesiology and community health professor, said. She led the research along with Jessica Damoiseaux, a Wayne State University psychology professor.

Many studies looking at the brain effects of aerobic exercise have shown a similar increase in hippocampus size over time, according to Gothe. She said the hippocampus is involved in memory processing and is known to shrink with age.

"It is also the structure that is first affected in dementia and Alzheimer's disease," she added.

Supporting these findings is a study published in the Journal of Alzheimer's Disease, which found that yoga and meditation are more effective than memory exercises for preventing the mental decline that often precedes Alzheimer’s.