Page 117 - JSOM Spring 2018

be mediated by smoking-related release of catecholamine. 72,132 Cessation of Smoking and Residual Effects
Blood flow and oxygen tension return to baseline values
within 30 to 50 minutes, emphasizing the transient nature It would seem reasonable that an effective injury prevention
of these effects. 131,133 Nonetheless, continuous smoking can strategy would be to stop smoking. In US Army Basic Com-
result in reduced oxygen and other nutrients to tissues, es- bat Training (BCT) recruits are not allow to smoke and thus
pecially those involved in the process of tissue renewal and smoking cessation begins at the onset of BCT. Yet, a recent
injury healing. meta-analysis found that the overall injury risk among prior
smoking recruits was 1.31 times greater than that of non-
smoking recruits despite smoking cessation. This suggests
17
Risk Taking
Besides physiological mechanisms, psychosocial factors must that smoking cessation does not immediately reverse the ef-
also be considered in accounting for the association between fects of prior smoking on injuries and there may be a period
cigarette smoking and injury. In civilian studies, smokers gen- of time before the injury risk (and/or healing ability) of former
erally scored higher on tests of risk-taking propensity. 134–136 smokers reaches that of nonsmokers. The literature suggests
Also, smokers had more motor vehicle accidents, more traf- that this time period may be dependent on the tissues involved
fic violations, less seat belt use, less physical activity, more and what physiological function is examined.
alcohol consumption, lower intake of fruits and vegetables,
and lower ratings on the importance of safety practices. 137–140 Bone
Heavy smoking (≥ 20 cigarettes/day) was much more likely to Several meta-analyses have found that the risk of fractures in
be associated with multiple risk behaviors. It is possible that former smokers was intermediate between that of smokers and
139
the higher risk-taking behavior of smokers manifests itself in a nonsmokers, suggesting that the effects of smoking on fracture
33,34,75
higher injury rate among smokers. risk are at least somewhat reversible. Five to 10 years
after smoking cessation former smokers had a considerably
reduced risk of hip fractures compared with current smok-
Muscle Tissue 154,155
Although no studies have found a direct effect of cigarette ers or had a risk similar to that of individuals who had
155,156
smoking on muscle injury (e.g., muscle stains), experimental never smoked. Another study found that after an average
studies suggest that muscle tissues is dysregulated in smokers. 9 years of smoking cessation, hip fracture risk was similar in
British military recruits who were smokers had smaller rec- smokers and former smokers, but risk for vertebral fractures
157
tus femoral volumes than non-smokers even after correcting was reduced in former smokers. Finally, a study of older
for body mass index. Cigarette smokers have been shown men in Sweden found that risk of any fracture persisted un-
141
158
to have less cross-sectional area of Type I (oxidative) muscle til 30 years after smoking cessation. Smoking cessation re-
160,161
159,160
fibers, a decreased rate of muscle protein synthesis, and in- duced the loss of BMD over periods of 1 to 3 years.
creased expression of genes that regulate muscle atrophy. 142–145 Taken as a whole, these limited data suggest favorable effects
These studies suggest that smoking increases muscle atrophy on bone health with smoking cessation, although the time
and catabolism among smokers. These effects may have func- course of these effects are not clear.
tional significance. Muscle strength was found to be lower in
smokers even after adjustment for physical activity, cardiore- Wound Healing
spiratory fitness, vitamin intake, alcohol consumption, and Several systematic reviews have examined the effects of smok-
body fat. 145,146 ing cessation on healing of surgical wounds and have attempted
to identify the optimal time presurgical smoking cessation
Smoking may have effects on protein deposition in muscle would minimize adverse effects. 162–164 One systematic review of
and other tissues throughout the body due to alterations in seven investigations found that smoking cessation for 4 weeks
androgen production and metabolism. Male smokers have reduced the overall complication rate by 20% compared with
162
lower testosterone levels in the testicular veins and a lower those who continued to smoke. A randomized controlled
in vitro secretion rates of androgen binding protein sugges- study of experimentally induced wounds that showed that
tive of testicular cell (Sertoli cell) dysfunction. In isolated wound infections were significantly fewer in individuals who
147
rat and mouse testicular cells (Leydig cells), testosterone and had ceased smoking for at least 4 weeks compared with indi-
165
androstenedione production is inhibited by nicotine in a dose- viduals who continued smoking. The physiological basis for
dependent manner. 148–150 Male rats exposed to cigarette smoke this appears involve, at least in part, the largely restored bacte-
166
for 60 days had degradation of testicular cells (Leydig cells) ricide functions of neutrophils and monocytes.
and lower plasma testosterone compared with nonexposed
rats. In dogs exposed to the equivalent of 12 cigarettes per Restoration of normal collagen metabolism after smoking ces-
151
day for 2 years, serum testosterone levels were decreased in a sation may take considerably longer. In individuals who had
dose-dependent manner and hepatic catabolism of testoster- stopped smoking, there was a tendency for a precursor of Type
one was increased. However, a whole body human study 1 collagen (procollagen type 1 amino-terminal propeptide) to
152
using stable isotope tracers found that the production rate of increase very slowly over 12 weeks (the maximal length of the
168
167
testosterone did not differ between smokers and nonsmokers study). Another study followed weekly urinary hydroxy-
but the metabolic clearance rate was higher in smokers. In proline/creatine levels (indicative of collagen metabolism)
153
summary, there is some evidence that smoking may exert ef- from individuals up to 14 weeks after they ceased smoking.
fects on testicular cell function 147,150,151 resulting in decreased It was estimated from mathematical modeling that hydroxy-
production of testosterone 147,152 but also some contradictory proline/creatine levels would return to the level of nonsmokers
evidence. The evidence for increased catabolism of testos- in about 71 weeks, among those who had previously smoked
153
terone in smokers is more consistent. 152,153 These could have 40 cigarettes or fewer per day, while it would take 120 weeks
long-term consequences in the turnover of muscle tissue and to reach the same level in those who had been smoking more
may make muscle-related injuries more common. than 40 cigarettes/day.
Smoking and Injuries | 111