Many people who reach middle-age start worrying about their future health. Will they get Alzheimer’s disease? What about type 2 diabetes? Is there a chance of heart disease? And is there anything they can do to prevent it. It turns out that there may be a “fountain of youth” against these chronic diseases – exercise.

A study out of the University of Texas Southwestern Medical Center looked at data from 18,670 healthy individuals from the Cooper Center Longitudinal Study who were an average age of 45 and had received Medicare coverage between 1999-2009. The participants’ fitness was assessed using a treadmill. The researchers also factored in the participants’ age, body mass index, blood pressure, cholesterol and glucose levels, alcohol use and smoking. However, they did not take into account the participants’ diet or genetic factors that could play a role.

The researchers used the Medicare claims over a 26-year period to gauge whether participants had developed eight chronic conditions, including heart disease, diabetes, Alzheimer’s disease and colon cancer. Their analysis found that a participant’s fitness level was significantly associated with a lower risk of developing chronic diseases over the next 26 years. For instance, the rate of chronic disease was 28 percent per year among men who scored in the lowest 20 percent of fitness scores. In comparison, the rate of chronic disease was 16 percent among men who were in the top 20 percent of fitness scores. Women saw a similar difference. The rate of chronic disease was 20 percent per year for women in the lowest 20 percent of fitness scores while the rate was 11 percent for women in the highest 20 percent of fitness scores. In an online commentary about this study, Dr. Diane Bild, who works in the Division of Cardiovascular Sciences at the National Heart, Lung and Blood Institute pointed to multiple studies that have found that cardiorespiratory fitness is strongly associated with longevity and reduced risk of chronic disease.

One concept that I found interesting was a comment that study author Dr. Jarett Berry made in an article on MedlinePlus. “We know from prior literature that higher-intensity exercise tends to translate into more fitness,” he said. “Walking is clearly better than doing nothing, but if you can make the choice between walking and jogging, then jogging is probably better for you.”

Why did I find Dr. Berry’s comment interesting? That’s because I just read a story by Dallas Morning News reporter Leslie Barker this morning that encourages a more varied workout. She described a trainer who devised an experiment for two of his clients. One was a devoted runner while the other preferred weights as well as exercises such as jumping jacks and push-ups. The trainer gave both the same workout as they exercises together. It turns out the runner nearly threw up before the end of the session. Barker quotes experts as saying that cross-training using complementary exercises can actually help a person perform better at his or her favorite form of exercise.