A new study out of France highlights an unexpected potential link between marijuana smoking and cataracts
Ready or not, a green wave is crashing on shores across the world. Cannabis has now been legalized or decriminalized in dozens of countries. Medical research on the negative effects of the drug, however, remains sparse. A near total ban on cannabis cultivation for almost a century has stymied scientific and medical research. But new research on this previously banned controlled substance is shedding new light on what negative effects it has on the human body, and especially eye health.
Sight up in smoke?
Enter a 2022 study published in the French Journal of Ophthalmology.1 This landmark investigation has circumvented historical difficulties in researching cannabis by making use of the U.K.’s Biobank, a large repository of historical data on participants recruited between 2006 and 2010. Noting an established connection between tobacco smoking and cataract risk, study authors analyzed data for potential correlations between cannabis and cloudy lenses.
Tobacco smoke has been found to increase the risk of the development of cataract,2 and especially nuclear cataract. And since weed smoke and tobacco smoke both contain a similar carcinogenic profile, a cannabis-cataract connection would seem to follow.
A Pot Twist
And indeed Lehrer and Rheinstein did find a connection, though not exactly of the variety anticipated. The U.K. Biobank data was collected and analyzed by Minerva, a Linux mainframe, to suss out potential correlations.
The first question explored was whether or not cannabis consumption accelerated the process of developing a cataract. Data parameters were lifetime instances of cannabis consumption (1-2, 3-10, 11-100, more than 100 times) and age of development of cataract, with 2358 subjects found matching the criteria.
Overall, the mean age of development of cataract was 56, with 8 years on either side representing a standard deviation. A surprisingly tidy trend was spotted in the data — the age of cataract onset gradually decreased as the number of times of cannabis consumption increased. For the 1-2 times group, average cataract onset was 57.55. For 3-10 times, it was 55.95; for 11-100, a stunning drop to 52.94; and for more than 100 times, a rebound to 53.3 (though it should be noted this group contained a paltry 33 patients who developed a cataract.
In other words, the more doobies you blaze, the earlier you get blinding lens haze. The data certainly suggests a mechanism at work speeding up the process of cataract development — but the search for a causal link was another story entirely.
A High Degree of Difference
This same quickening effect in tobacco smoke was not observed. And not only that, but when data on a potential link between cannabis use and cataract risk was analyzed, the picture got even cloudier.
Propensity score matching was used to determine if smoking marijuana and smoking tobacco increase the chances of an individual to develop cataracts. For the wacky tobacky, the answer to this question was no. And just as with age of cataract onset, the results for regular old tobacco were completely different, just as the data in a previous study2 also found a link between tobacco use and increased risk of cataract development.
So what gives? How can two substances similar in carcinogenic profile produce such wildly different results? Though this study was limited by leaning so heavily on data, the authors pointed out one key avenue of investigation — pesticides. Due to lack of regulation, pesticides, which have been noted for their adverse impact on eye health,3 have been far more likely to be found in cannabis than in tobacco, which is heavily tested and regulated.
Despite all this, of course, more investigations are necessary, said Lehrer and Rheinstein. Data on cataract type, for example, is sorely needed for any attempt to describe the relationship between cannabis and cataract.
- Lehrer S, Rheinstein PH. Marijuana smoking and cataract. J Fr Ophthalmol. 2022;45(3):267-271.
- Kelly SP, Thornton J, Edwards R, Sahu A, Harrison R. Smoking and cataract: review of causal association. J Cataract Refract Surg 2005;31:2395-2404.
- Jaga K, Dharmani C. Ocular toxicity from pesticide exposure: a recent review. Environ Health Prev Med 2006;11:102–7.