01.05.2014

Image from MedPageToday

by Crystal Phend
Senior Staff Writer, MedPage Today

The cataract risk associated with smoking slowly fell after ceasing tobacco use, although not to the level of a never-smoker, a Swedish population-based study showed.

Smoking more than 15 cigarettes per day was associated with 42% higher likelihood of a cataract surgery during 12 years of follow-up, Birgitta Ejdervik Lindblad, MD, PhD, ofÖrebro University Hospital in Örebro, Sweden, and colleagues found.

After having quit for 20 years, that risk had declined to a relative 21% above that of never-smokers, the researchers reported online in JAMA Ophthalmology.

The risk declined significantly with time (P<0.001), but “the higher the intensity of smoking, the longer it takes for the increased risk to decline,” the researchers noted.

Even lighter smokers with a fewer-than-15-a-day habit remained at significant risk 2 decades after quitting (rate ratio 1.13, 95% CI 1.04-1.24).

“These findings emphasize the importance of early smoking cessation and preferably the avoidance of smoking,” Linblad’s group concluded.

Plenty of prior studies have shown cataract and other ocular risks from smoking, so “eye care professionals should encourage people to stop smoking,” too, they recommended.

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,” Lindblad and colleagues explained.

“Cigarette smoke also contains toxic metal ions, and cadmium can accumulate in cataractous lenses of smokers,” they added. “Cadmium may affect anti-oxidative lens enzymes such as superoxide dismutase and glutathione peroxidase, thereby weakening the defense against oxidative damage and hastening cataract development.”

Their analysis included 44,371 men in the Cohort of Swedish Men study ages 45 to 79 years, among whom 25% reported smoking and 39% had been smokers, based on questionnaire responses regarding smoking habits and lifestyle factors.

During 12 years of follow-up via the Swedish National Day-Surgery Register, and local registers of cataract extraction in the study area, an age-adjusted 13% had cataract extractions.

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, “and therefore having the greatest clinical and public health importance.”