Long-term heavy tobacco smoking can lead to potentially harmful structural and functional changes in skeletal muscle outside the lungs, even in smokers who don't have chronic obstructive pulmonary disease (COPD), a new study suggests.
Smoking is the major cause of COPD, but relatively little is known about the effect of smoking on skeletal muscle. Skeletal muscles are striated and usually attached to the skeleton.
By exerting force on the bones and joints, the skeletal muscles contract to produce movement. Tobacco smoke contains more than 4 700 chemicals that are potentially harmful to skeletal muscle.
How the study was doneAccording to their report, published in the medical journal Chest, the investigators observed significantly reduced cross-sectional area of two types of muscle fibres in smokers compared with non-smokers.
For their study, Dr Maria Montes de Oca from Hospital Universitario de Caracas, Venezuela and colleagues compared the vastus lateralis muscle, which originates in the thigh bone extends to the shin bone, in 14 heavy smokers without COPD and 20 healthy non-smokers. Subjects in both groups led sedentary lifestyles.
Smokers were also more apt to show potentially harmful metabolic changes including an imbalance of oxidant and antioxidant chemicals, suggesting "preferential damage of oxidative fibres" among smokers, the investigators note.
The results also suggest that tobacco smoke alters the normal process by which the body generates nitric oxide, a chemical that helps open small blood vessels.
What the results reveal
This alteration could lead to hypoxia (low oxygen levels), which in turn may explain the fibre atrophy observed in the smokers.
The writer of a commentary published with the study reminds readers that the smokers in this study had normal airway function.
"It is remarkable," according to Dr Peter D. Wagner of University of California, San Diego, "that although the portal of entry of tobacco products was respiratory, there were systemic but not respiratory changes found."
Why did the lungs seem to escape the effects of smoking, yet distant organs (in this case the muscles) have substantial structural changes? "As is so often the case, one question answered gives rise to so many more," Wagner notes. – (Reuters Health)
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