Genetics may be to blame for exercise intolerance

This article explains how exercise intolerance may have a genetic component, although does not seem to be a hereditary condition.

Some cases of exercise intolerance have been linked to mutations in a gene found in the mitochondria, the “powerhouses” of the cell, according to a study.

Exercise intolerance is a condition in which a person experiences extreme fatigue, muscle pain or cramps after minimal exercise. Mitochondria provide energy that muscles require to function, so a defect in these could severely limit the ability to exercise.

Mitochondrial DNA — which is separate from DNA found in the nucleus, or control center of the cell — is inherited directly from the mother, so if a child has a disorder linked to the mitochondria, the mother usually also has it.

However, the research team from the Columbia College of Physicians and Surgeons in New York, found that in the patients studied, there was no maternal link to the mutation, and no evidence of the mutation in tissues other than muscles. This suggests that mutation is not inherited but occurs in the embryo, the team suggests. Five patients with exercise intolerance and no family history of the disease enrolled in the study.

Analyses of the patients’ cells revealed that all had defects in respiratory chain enzymes, which are used by mitochondria to make substances that store energy for muscles. Sophisticated techniques narrowed the deficiencies down to mutations in the mitochondrial cytochrome b gene.

The investigators conclude that such mitochondrial gene mutations may be common, and recommend that physicians consider this as a possible diagnosis in patients with “the often elusive symptoms of aches, pain, and cramps.”

No treatments have been developed for this condition, but as a therapeutic course for the patients, researchers suggest “genetic counseling” to explain to the patients that they will not pass their disease onto their children. Also, patients can engage in “appropriate exercise programs,” which might have some benefit, they add.

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Can statins cause fatigue and exercise intolerance?

Researchers delving into the side effects of statins found evidence that the popular cholesterol-lowering drugs may sap energy levels in users.

The study indicates that statin drugs may contribute to a drop in energy and fatigue upon exertion.

The danger of the potential adverse effect was particularly enhanced in women.

Lead author of the study, Dr. Beatrice Golomb, associate professor of medicine at the University of California-San Diego stated, "We found that even at comparatively modest doses, statins were associated with a not-inconsequential drop in energy in some patients, a rise in fatigue with exertion in others and sometimes both.

She added, "This was true for both men and women. But it appears to be more of a problem for female patients."

Study Details
In a study designed to investigate whether statins can cause energy drain and exercise intolerance for users, the researchers tracked 1,016 healthy adults (700 men and more than 300 women) from the San Diego region.

The participants were all aged 21 years or older with elevated LDL or ‘bad’ cholesterol. However, none had a history of heart disease or diabetes.

As a part of the study, they were randomly assigned to receive either a placebo or 40 milligrams of Pravachol (pravastatin), the most water-soluble statin, 20 mg of Zocor (simvastatin), the most fat-soluble statin every evening before retiring for six months.

During the study, the volunteers were asked to rate their energy and fatigue levels on a five-point scale, from "much worse" to "much better." In addition they were questioned how they felt after exercising.

Outcome of the study
The study found those placed on statins were more likely to report lower energy levels and more fatigue with exertion compared to people assigned to the placebo.

The effect was more pronounced in women, with 40 percent experiencing weariness with exertion and a drop in energy while taking the daily dose.

Dr. Golomb says, “Energy is central to quality of life. Exertional fatigue not only predicts actual participation in exercise, but lower energy and greater exertional fatigue may signal triggering of mechanisms by which statins may adversely affect cell health.”

Based on the study findings, the researchers suggest that medical professionals should weigh the pros and cons before prescribing statins to people.

The findings were reported online June 11 in Archives of Internal Medicine.

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