We all know children are shortsighted, but parents are often shortsighted too. Of course health habits influence the sick days from school, but childhood habits also influence their life expectancy in later years. Before the teenage years are over, a child’s longevity may be determined by habits that have already done harm.

Since 1900, life expectancy has increased from 48 years for men and 51 for women to 75 for men and 79 for women in 2000, but now Jay Olshansky in the New England Journal of Medicine predicts the trend will reverse due to obesity. Fifty percent of U.S. children will be overweight by 2010, the International Journal of Pediatric Obesity reports. More children will be at risk due to being overweight, than from drugs, alcohol, or teenage pregnancies. Chances of being overweight grow from 50 to 70 percent for children of overweight parents. For every pound overweight your child is as a young teenager, his prospects for longevity are reduced a little.

Type 2 diabetes was a rare disease in 1900, but now 7 percent (21 million) of Americans are diabetic and 42 million are pre-diabetic. Diabetics can manage their problem with careful eating, but their enjoyment of life is forever limited. A precursor to diabetes is being overweight. Fifteen percent of white adolescents are obese and the percentage rises to 24 percent for many minority groups.

We all know smoking shortens life expectancy on average by about as many days as you smoke. Of course, every smoker thinks he is an exception. My uncle surprised us all by living to be 80 and died with his pack of cigarettes on his night stand, but he lived a miserable coughing life due to emphysema.

Recently my doctor asked me when I had stopped smoking. I said I knew the exact day - Thanksgiving, November 22, 1962.

He said, “Oh good, you know the date. It gives me a chance to use my tables to show how long you are likely to live.”

“The day makes a difference?” I asked.

“Not much, but every day of non-smoking makes a little difference.”

Suddenly I wished I had quit even earlier.

The next important longevity factor is a person’s alcohol habit. Kids who start drinking early are at risk for long-term dependency and then other substance abuse. Later on, if they drink and drive, they risk adding to another gruesome statistic since traffic accidents are still our number one teenage killers. Alcoholism and other drug dependence will of course reduce longevity.

Give your child a chance at a long and active life. Set the right example. Insist on no smoking, reasonable eating and drinking habits and regular exercise in the growing years.