The longer I’ve been a health writer, the more convinced I've become that exercise is the true fountain of youth.

That belief was reinforced on Monday with the publication of four new articles in the Archives of Internal Medicine linking physical activity with healthier aging.

“The promotion of physical activity may be the most effective prescription that physicians can dispense for the purposes of promoting successful aging,” wrote Jeff Williamson, MD, and Marco Pahor, MD, of the University of Florida’s Institute on Aging, in an editorial that accompanied the studies.

The health benefits of exercise, they added, include preventive effects related to “numerous age-related conditions, such as osteoarthritis, falls and hip fracture, cardiovascular disease, respiratory diseases, cancer, diabetes mellitus, osteoporosis, low fitness and obesity, and decreased functional capacity.”

That list alone (and it could be easily extended to add other illnesses and conditions, including mild depression) should be enough to get each of us hitting the weight rooms, pools, walking paths, golf courses, tennis courts or wherever else we can give our heart and our other muscles a good workout — both aerobically and anaerobically.

Sharper thinking skills
Two of the studies published on Monday looked at the relationship between physical exercise and thinking skills (cognitive function). One study followed more than 3,000 people, aged 56 and older, for two years. None showed signs of cognitive impairment at the start of the study. Those participants who engaged in moderate or intense physical activity (for example, walking, bicycling, swimming, or gardening) at least once each week were less likely than those who never exercised to experience a decline in thinking skills.

Specifically, the incidence of new cognitive impairment among the study’s participants was 13.9 percent for those who didn’t exercise at all, 6.7 percent for those who exercised once or twice a week, and 5.1 percent for those who exercised three or more times a week.

Resistance training helps
In another study, Canadian researchers randomly assigned 155 women, aged 65 to 75 years, to either a once-weekly or twice-weekly resistance-training group (using both machine- and free-weights) or to a twice-weekly group that took a class in developing better muscle tone and balance through stretching, range-of-motion, core-strength and tai chi-like exercises.

The study found that the women who stuck with the resistance-training program for 12 months improved their scores by up to almost 13 percent on a series of cognitive tests (not memory, though), while the women in the tone-and-balance group exhibited a decline in cognitive skills of 0.5 percent.

Stronger bones
A third study randomized 246 elderly German women either to a multipurpose exercise program that emphasized intense physical activity or to a program that encouraged general well-being and low-intensity physical activity.

After 18 months, those in the high-intensity program had significantly denser spines and were less likely to experience a fall than their peers in the low-intensity program. There was no significant difference between the groups, however, in their risk of developing cardiovascular disease.

Better quality old age
The fourth study examined data from more then 13,000 participants in the long-running Nurses’ Health Study. It found a strong correlation between “midlife leisure-time physical activity and the odds of successful survival or exceptional overall health in later life.”  “Successful” was defined as living beyond age 70 without debilitating chronic diseases or significant limitations in physical or mental function.

The final word?
Each of these studies had its limitations, of course. The randomized, controlled studies were very small, for example, and the larger non-randomized studies revealed only an association, not a cause-and-effect connection, between exercise and better health.

To try to determine once and for if there is a strong connection between exercise and healthier aging, a new major randomized multicenter study, called Lifestyle Interventions and Independence for Elders (LIFE), is getting under way.  Recruiting begins soon.

It’ll be years before we know those results, however. In the meantime, if you aren't already doing so, get out there and exercise (after talking it over with your doctor, of course).

As Williamson and Pahor noted in their editorial: “Along with the expected results of the LIFE study, the 4 new studies in this issue of the Archives, and the evidence from clinical studies over the past 25 years, we have never had greater reason to be hopeful regarding the potential for exercise to become a proven and generalizable strategy for promoting successful aging in the expanding population of older adults.”