Stop smoking, grow faster
Smokers' muscle tissue breaks down more quickly than the muscle tissue of non-smokers. Researchers at the Copenhagen Muscle Research Centre discovered this when they compared muscle cells from the quadriceps muscle of 8 smokers and 8 non-smokers. Smokers produce more myostatin, a hormone that inhibits muscle growth.
As the western population ages, sarcopenia or age-related loss of muscle mass is becoming more common, so researchers are looking for ways to help elderly people maintain muscle strength. According to some epidemiological studies, elderly smokers are more likely to develop sarcopenia than non-smokers. So the Danish researchers set up a lab experiment to find out exactly what effect smoking has on muscle cells.
The researchers compared the muscle cells of 8 smokers, who all smoked over 20 cigarettes a day, with muscle cells of 8 non-smokers of the same age. The subjects did no sport. Before taking a cell sample from the subjects' thigh muscle, the researchers gave the subjects a dose of labelled leucine. This enabled them to see whether the cells absorbed amino acids and built them into muscle protein.
The cells of the smokers absorbed amino acids just as well as the non-smokers' cells did. But their mixed-muscle protein fractional synthesis rate - their muscle protein manufacture, in simple language - was lower, analysis of the muscle cells showed.
Smoking causes inflammatory reactions. The concentration of inflammatory factors TNF-alpha, CRP and Interleukine-6 did not increase in the smokers' blood. Nor did smoking increase the activity of the TNF-alpha gene in the muscle cells. So inflammatory processes would seem to have nothing to do with the catabolic effect that smoking has.
"Smoking is a potent inhibitor of the muscle protein synthetic machinery", the researchers sum up in their conclusion.
Am J Physiol Endocrinol Metab. 2007 Sep; 293(3): E843-8.
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