Marijuana smoking and cataract

Cigarette smoking is a well-known risk factor for cataract and other ailments, including heart disease, lung cancer, and chronic obstructive pulmonary disease. Cannabis smoke, like tobacco smoke, contains a comparable variety of carcinogenic and toxic compounds.

In the present study, we analyzed UK Biobank data to determine whether smoking cannabis, like cigarettes, might be related to cataract.

Our analysis included all UK Biobank subjects with cataracts and information on cannabis and cigarette smoking habits. The diagnosis of cataract was ascertained using the 10th Revision of the International Classification of Diseases (ICD10), H25. The age at diagnosis of cataract was obtained from UK Biobank data field 4700. Cannabis information was recorded in UK Biobank category 143, data field 20453, ever taken cannabis.

Subjects who used cannabis 11-100 times or more were significantly younger (4-5 years) when they developed cataract than subjects who never used cannabis. To determine the relationship of current cigarette smoking to cannabis use and age at cataract, the univariate general linear model of SPSS was used, dependent variable age at cataract, fixed factor cannabis use, random factor pack years of cigarettes smoked. Cannabis use was significantly related to age at cataract diagnosis (P<0.001) and independent of the effect of pack-years of cigarettes smoked (P=0.008). Linear regression revealed an insignificant relationship between pack-years of cigarette smoking and age at cataract diagnosis (P=0.073). To further evaluate the relationship of cannabis to cataract, propensity score matching was performed. We identified 28,432 subjects with cataract. Current cigarette smoking and age were covariates; cannabis use (yes/no) was the indicator variable. Current cigarette smoking was significantly associated with a 1.2 odds ratio for cataract. Cannabis use was not significantly associated with the odds ratio for cataract.

Like tobacco smoke, cannabis smoke contains thousands of organic and inorganic chemical compounds. Cannabis tar is chemically similar to tar found in tobacco smoke, and over fifty known carcinogens have been identified in cannabis smoke, including nitrosamines, reactive aldehydes, and polycyclic hydrocarbons. Thus, the association of cannabis with cataract that we report here is not entirely surprising. Further studies are warranted.