As we age, we get shorter. Starting about age 40, we lose about four-tenths of an inch in height each decade. By age 70, men lose, on average, about an inch and a half in height; women lose up to 2 inches.
As we get older, the disks between the vertebrae of the spine dry out and become thinner, causing the spine to shrink. It also doesn't help that the arches of our feet flatten as we age.
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And we tend to lose muscle mass. When we lose it in the abdomen, our posture deteriorates. We tend to lean forward, which makes it appear we've shrunk more than we really have.
So shrinkage is a natural part of aging. But recent research conducted by economists at Harvard University, the University of Southern California and Peking University indicates that shrinkage can be controlled.
The data they derived from a long-term survey of 17,078 adults in China beginning at age 45 indicates that lifestyle choices exert considerable influence on how much height we lose.
Urban dwellers lost much less height than country people, the economists found. Chinese men who completed primary school lost nearly a centimeter (0.4 inches) less height than men who were illiterate. Men who completed high school retained an additional centimeter in height. Because the average loss of height for men in the survey was 3.3 centimeters, education could account for up to a 57 percent difference in height loss.
The correlation between education and height loss wasn't as strong for women. The women in the survey who completed primary school shrank 0.6 centimeters less than illiterate women. The average overall height decrease among women was 3.8 centimeters.
Those who lost more height also tended to perform more poorly on tests of cognitive health, such as short-term memory, ability to perform basic arithmetic and awareness of the date, the researchers said.
The economists viewed the level of education as representing a person's knowledge of habits that are conducive to good health and having access to better medical care.
Poor diet, lack of exercise and smoking lead to greater height loss, said Dr. Christine Herb, who practices internal medicine with an emphasis on geriatrics at Allegheny General Hospital in Pittsburgh.
The survey indicates that "making lifestyle modifications is beneficial at any point in life," Herb said.
A key variable in height loss is osteoporosis (a loss of bone density), she said. Those who eat a well-balanced diet rich in calcium and vitamin D, who don't smoke, drink alcohol in moderation and exercise regularly are less likely to suffer from it.
"Exercise helps to keep our bones strong," Herb said. Resistance exercises, such as weightlifting, are most helpful, but any exercise is beneficial.
"Walking can be prescribed for almost any individual at any age," she said.