Inactivity Greater Factor In Insulin Resistance Than Aging

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September 19, 2008

Inactivity may be a greater factor in insulin resistance than aging

Inactivity or adiposity may be a greater factor in insulin resistance than aging

An article entitled, “Endurance exercise as a countermeasure for aging,” published online on August 20, 2008 in the journal Diabetes, concluded that the reduction in insulin sensitivity that often occurs in one’s later years may not be an inevitable consequence of aging.

Researchers at the Mayo Clinic College of Medicine in Rochester, Minnesota sought to determine whether long-term endurance training could improve lowered insulin sensitivity (a factor in the metabolic syndrome, which is more prevalent with aging) and mitochondrial dysfunction, a widespread condition of aging which has been associated with declines in insulin sensitivity. (Mitochondria are organelles within the cell that produce energy.) The team enrolled 22 adults aged 18 to 30 years, and 20 adults between the ages of 59 to 76 years for the current study. Participants were divided into those who reported less than 30 minutes of exercise per day two times weekly, and those who participated in at least one hour of running or cycling per day six days per week over the past four years. Blood samples were tested for lipids, glucose, and other factors, and dual x-ray absorptiometry was used to measure fat and fat free mass. Insulin sensitivity, whole-body peak oxygen uptake, muscle mass, mitochondrial function, and SIRT3 expression were also measured. SIRT3 is a mitochondrial gene of the sirtuin family that has been linked with longevity, whose expression has been found to increase with calorie restriction.

Older participants had less muscle mass, greater adiposity and diminished whole-body oxygen peak, however, among those that were exercised trained, oxygen peak was higher and fat was lower than in the age-corresponding sedentary groups. For trained subjects, insulin sensitivity was significantly greater compared to the sedentary groups, with no significant difference between young and old groups noted. The age-related decrease in mitochondrial oxidative capacity observed in older individuals was not seen in exercised-trained participants. Although mitochondrial DNA was higher in trained compared with sedentary participants, it remained greater in younger than in older subjects. No decline of SIRT3 expression with age was observed among trained adults, although a significant decline was noted in older sedentary participants.

In their summary of the findings, the authors write that “endurance exercise-trained young and older people have substantially higher insulin sensitivity than the sedentary groups and no differences between young and older people were observed in either sedentary or exercise trained groups. Secondly, in contrast, we found age-related declines in various markers of mitochondrial function in the sedentary groups, but these age-related differences were partly, but not completely, abolished in people who practice regular endurance exercise. Finally, we show that endurance exercise may exert similar potentially lifespan-enhancing effects as caloric restriction through elevated SIRT3 expression in both young and older adults.”

The authors conclude that exercise could have similar effects on life-span as those observed with calorie restriction in other organisms.

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Getting the most from exercise

Exercise has been shown to increase life span by an average of one to four years for people who engage in moderate to difficult exercise routines (Jonker JT et al 2006; Franco OH et al 2005). Better yet, those additional years will be healthful years because exercise benefits the heart, lungs, and muscles. Even moderate levels of exercise have been documented to stave off many dreaded diseases of aging. Walking briskly for 3 hours per week reduces one’s chances of developing many chronic health problems (Chakravarthy MV et al 2002). Exercise may also alleviate depression and enhance self-image and quality of life (Elavsky S et al 2005; Schechtman KB et al 2001).

There are many benefits to a program of regular exercise. In addition to enhanced self-esteem, exercise can promote weight loss and aid in the prevention of a number of diseases, including heart disease and diabetes. In addition, the following nutrients have been shown to enhance muscle function, promote quicker recovery after exercise, and increase strength:

  • Carnitine—1000 to 2000 milligrams (mg) daily
  • Carnosine—1500 to 3000 mg daily
  • Branched-chain amino acids—containing at least 1200 mg L-leucine, 600 mg L-isoleucine, and 600 mg L-valine
  • Glutamine—500 to 1000 mg daily
  • Whey protein—consider taking 20 to 80 grams (g) whey protein daily. It is most important to consume whey protein before and immediately after your exercise session to make sure adequate protein is available to depleted muscles.
  • PPC—900 to 1800 mg

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