Tobacco smoking is a significant class I risk factor for cataract development, says a report published in the British Journal of Ophthalmology. Researchers also identified several risk-mitigating dietary factors for age-related eye diseases, such as age-related macular degeneration (AMD).
The researchers evaluated 64 associations from 25 meta-analyses and 41 associations from 10 qualitative systematic reviews. It identified class I evidence only for the association between “smoking” and cataract development, and class II evidence for the associations between “ever smoking” and cataracts. The researchers also describe a class III association between “fish consumption” and AMD, which was actually a downgrade from prior research categorizing the association as class II. Class III evidence was identified for associations between the dietary intake of omega-3 polyunsaturated fatty acid (PUFA), lutein, zeaxanthin, vitamin C, and the risk of cataract.
“All of these nutrients have antioxidant properties, which protect against oxidative insult to the lens, and thus may prevent or delay the onset of cataract,” according to the researchers. Foods rich in these micronutrients include eggs, fruits, and green vegetables.
The study also confirms 2 potential protective factors associated with AMD: dietary omega-3 PUFA intake (OR: 0.82 [0.73–0.92]) and fish consumption, fish being a strong source of omega-3 PUFA (OR: 0.78 [0.71–0.85]). Omega-3 PUFAs have antioxidative and anti-inflammatory properties, which the researchers believe account for their beneficial effects
The researchers explained that the results of this study could provide grounds for encouraging the public to take measures to prevent AREDs, such as smoking cessation as well as the consumption of diets rich in nutrients such as omega-3 PUFA, lutein, zeaxanthin, and antioxidant vitamins.
‘First, smoking causes additional oxidative damage, which is reported to play a role in various diseases such as cataract and AMD, consistent with our finding that the evidence for current smoking as a risk factor for AMD was suggestive (class III),” the researchers explain. “Second, the heavy metals contained in tobacco have a direct toxic effect on the lens. Third, serum levels of cyanide and aldehyde are elevated in smokers, which may contribute to lens opacification.”
Study limitations include the low or critically low quality of included systematic reviews; variation among the studies included in terms of diagnostic methods, study design, and populations examined; and possible bias due to the study’s nature.
Kai JY, Zhou M, Li DL, et al. Smoking, dietary factors and major age-related eye disorders: an umbrella review of systematic reviews and meta-analyses. Br J Ophthalmology. Published online December 8, 2022. doi:10.1136/bjo-2022-322325.