Smoking 15 cigarettes daily linked to 42% risk of cataract surgery
Smoking a pack a day of cigarettes may double the risk of developing cataracts. Smokers are at particular risk for cataracts located in the nuclear portion of the lens, which limit vision more severely than cataracts in other sites. However, the effect of smoking cessation on the risk of cataracts is uncertain.
Dr. Birgitta Ejdervik Lindblad, MD, PhD, School of Health and Medical Sciences, Örebro University, Institute of Environmental Medicine, Karolinska Institutet, Stockholm and Department of Ophthalmology, Örebro University Hospital, Örebro along with colleagues examined the link between smoking cessation and the risk of cataract extraction.
This new study included 44,374 men, aged 45 to 79 years, participating in the Cohort of Swedish Men who in 1997 completed a self-administered questionnaire on smoking habits and lifestyle factors, with 25% reported smoking and 39% had been smokers.
The men were followed up from January 1, 1998, through December 31, 2009. The cohort was matched with the Swedish National Day-Surgery Register and local registers of cataract extraction in the study area.
During 12 years of follow-up, 5,713 incident cases of age-related cataract extraction. Smoking intensity and cumulative dose of smoking were associated with an increased risk of cataract extraction.
Current smokers who smoked more than 15 cigarettes a day had a 42% increased risk of cataract extraction compared with never smokers after adjustment for age and other potential risk factors.
Smoking cessation significantly decreased the risk for cataract extraction with time. After more than 20 years since stopping smoking, men with a mean smoking intensity of more than 15 cigarettes per day had a 21% increased risk of cataract extraction compared with never smokers.
Among men who smoked 15 cigarettes or less per day, the effect of smoking cessation was observed earlier, but more than 2 decades after smoking cessation, the risk of cataract extraction did not decrease to the level of never smokers.
In their conclusion the researchers write “Smoking cessation seems to decrease the risk of cataract extraction with time, although the risk persists for decades. The higher the intensity of smoking, the longer it takes for the increased risk to decline. These findings emphasize the importance of early smoking cessation and preferably the avoidance of smoking.”
The presumed mechanism for this risk is that "smoking increases the oxidative stress in the lens by generating free radicals and reduces the plasma concentration of several antioxidants, such as ascorbic acid, explain the researchers.
The researchers add "Cigarette smoke also contains toxic metal ions, and cadmium can accumulate in cataractous lenses of smokers.” "Cadmium may affect antioxidative lens enzymes such as superoxide dismutase and glutathione peroxidase, thereby weakening the defense against oxidative damage and hastening cataract development."
Limitations of the study included possible misclassification of self-reported smoking history, no assessment or control for sunlight or UV exposure, and lack of data on subtype of cataracts, although all were severe enough to cause visual impairment requiring lens extraction.
This study appears in JAMA Ophthalmology.