In 2010, 40.3 million people in the United States were 65 and older, accounting for 13 percent of the total population. This age group was larger than in any other decennial census, up from 31.2 million in 1990 and 35.0 million in 2000.

And this number will continue to grow. By 2050, the projected population of people 65 and older is 88.5 million, which would comprise 20 percent of the total population at that time.

As we approach those golden years from 65 on, we often become concerned about how well we will function.

We see the signs of cognitive decline in our older family members, friends and colleagues — forgetfulness, dwindling attention span and decreased problem-solving capacity. Yet we also know people in their 80s and 90s who are as mentally sharp as their younger counterparts. These superagers are different.

"Superagers," a term coined by neurologist Marsel Mesulam, are those 80 years and older whose memories and attention spans are on par with healthy, active people in their 50s and 60s. Despite their DNA, superagers live long and healthy lives and continue to do the things they love.

In fact, a group of recent studies shows that our genes account for only 20-30 percent of the reason why people live past age 86. So, the good news is that "superaging" may well be under our control.

In a new ground-breaking study, researchers found that the brains of superagers demonstrate a greater resistance to typical memory loss, dementia and the normal rate of decline that we see in average elderly persons. SuperAgers are managing to strike a balance between life span and health span, really living well and enjoying their later years of life.

Amanda Cook, MA, Northwestern University in Chicago, and colleagues found that while the brain cortex of both superagers and their cognitively average peers showed shrinkage over 18 months, the rate of cortical brain atrophy in the adult controls was about double that of the superagers.

The study took place from April 2010 to May 2015 and involved 36 individuals with intact daily functioning and stable cognitive status from the community. Participants included 24 superagers (75 percent women) and 12 cognitively average elderly adults (42 percent women) who were similar in age (mean 83 years), levels of education (15 years) and intelligence.

Using magnetic resonance imaging, the scientists measured the thickness of the cortex in the 36 participants to determine the approximate health of their brain. While both groups had significant whole-brain cortical volume loss over 18 months, the annual percent change (APC) was significantly greater in the cognitively average elderly compared with superagers (2.24 percent versus 1.06 percent, P=0.02).

This study demonstrates that the brains of superagers shrink at a much slower rate than their age-matched peers and may be related to a thicker cortex. Cook agreed that modern medicine has extended the average human life span but points out that increasing age is often accompanied by typical cognitive decline, or in some cases dementia.

However, the existence of superagers suggests that age-related cognitive decline is not inevitable. According to Nir Barzilai, MD, director of the Albert Einstein College of Medicine Institute for Aging Research, who was not involved in the study, the results support the theory that chronological age and biological age are not the same, but the biological factors and genetic explanations for such resiliency need to be further explored.