Findings from a recent study published in Eye used accelerometer data from more than 77,000 UK Biobank participants to test whether objectively measured physical activity (PA) protects against senile cataract (SC).
Give me some background first.
Some context: Cataracts are among the leading cause of vision impairment and blindness worldwide, with unaddressed cataract accounting for 94 million cases of distance vision impairment or blindness.
Earlier research had already flagged PA as a possible protective factor: A Swedish cohort of 52,660 adults found high long-term PA associated with lower age-related cataract risk.
However, nearly all of that evidence came from self-reported questionnaires, which carry recall bias and social desirability bias. Neither applies to a device that measures movement directly.
Now, talk about the study.
Investigators paired a prospective cohort analysis with two-sample Mendelian randomization (MR), which uses genetic variants as instrumental variables to work around confounding and reverse causality.
The question: Does intensity-specific PA reduce cataract risk, and is the relationship causal?
In practice: PA was captured with triaxial accelerometers worn continuously for 7 days, then sorted into light (LPA), moderate (MPA), and vigorous (VPA) intensity bands. Moderate-to-vigorous PA (MVPA) was calculated as MPA minutes plus double the VPA minutes.
Who was included in the study?
Screening started with 502,370 UK Biobank participants at baseline and landed at 77,123 after excluding people without accelerometer data, those with poor wear-time quality, anyone with cataract at baseline, and those missing covariate data.
Demographics: Mean age was 55.67 years (standard deviation 7.81). Mean follow-up ran 6.3 years (interquartile range: 5.3 to 7.3), covering 2006 to 2021 and 488,960 person-years.
Outcome: 1,194 incident SC cases (657 women, 537 men), identified from hospital inpatient and primary care records using International Classification of Diseases, Tenth Revision (ICD-10) and ICD-9 codes.
Findings?
Compared with less than 150 min/week, MVPA of 150 to 600 min/week carried a 21% lower risk of incident SC (hazard ratio [HR] = 0.79, 95% confidence interval [CI]: 0.68 to 0.91).
Broken into bands after full adjustment:
- MPA 150 to 299 min/week: HR = 0.79 (0.64 to 0.98)
- MPA 300 to 599 min/week: HR = 0.79 (0.64 to 0.97)
- MVPA 300 to 599 min/week: HR = 0.79 (0.64 to 0.98)
- MVPA ≥600 min/week: HR = 0.79 (0.62 to 1.00)
Worth noting: LPA and VPA on their own showed no significant association with SC risk.
Tell me more.
The relationship between physical activity and cataract risk wasn’t simply “more is better.” For MPA, cataract risk fell as activity increased, reaching its lowest point at about 539 minutes per week, before rising again at higher levels. The apparent protective range was about 440 to 618 minutes per week. MVPA showed a similar pattern.
The genetic arm: Genetic data also supported a protective effect of MVPA. People genetically predisposed to higher MVPA had 32% lower odds of cataract (OR 0.68; 95% CI, 0.53–0.88). The association remained significant after additional statistical adjustment (OR 0.76). No causal association was found for light activity, moderate activity alone, or overall physical activity.
Subgroups: The MPA 300 to 600 min/week association held across adults aged 50 and older (HR = 0.58, 0.47 to 0.72), men (HR = 0.61, 0.46 to 0.81), current smokers (HR = 0.70, 0.53 to 0.92), patients with hypertension (HR = 0.74, 0.59 to 0.92), patients with hyperlipidemia (HR = 0.76, 0.58 to 0.98), and those with no prior cancer diagnosis (HR = 0.78, 0.63 to 0.97).
Reverse causality check: A 1-year landmark analysis produced even larger effect sizes. MPA of 150 to 299 min/week cut risk by 30% (HR = 0.70, 0.54 to 0.91, P = 0.007), and 300 to 599 min/week cut it by 31% (HR = 0.69, 0.53 to 0.88, P = 0.002).
Limitations?
Cases were identified from medical records, so early or asymptomatic lens opacities went uncounted. ICD codes also blur the line between lens opacity, clinically diagnosed cataract, and post-surgical status.
- The authors noted this non-differential misclassification would dilute the true association, making their estimate a conservative one.
Other considerations:
- UK Biobank participants skew healthier than the general population, which limits generalizability
- The model left out several known cataract risk factors: genetic predisposition, corticosteroid use, ocular trauma, prolonged ultraviolet exposure, and radiation therapy
- Residual reverse causality is still possible. SC progresses slowly, and preclinical changes like glare or reduced contrast sensitivity could quietly push people to move less years before diagnosis
- The MR instruments showed notable heterogeneity for MVPA, VPA, and overall PA
Expert opinion?
No outside expert commentary was included in the study.
Their position: Oxidative stress drives lens protein denaturation and opacification, and long-term regular exercise may counter it by strengthening endogenous antioxidant defenses. The authors pointed to earlier work showing 10 to 12 weeks of moderate-intensity exercise can bring circulating pro-inflammatory biomarkers down to levels seen in younger people.
They also offered a theory for the upper limit: prolonged high-intensity exercise may cancel out those antioxidant and anti-inflammatory gains by triggering recurrent transient oxidative stress and systemic inflammation.
Take home.
The WHO target of at least 150 minutes of moderate-intensity activity per week appears to do double duty for the lens.
For middle-aged and older patients asking what they can actually do about cataract risk, 150 to 600 minutes of moderate-to-vigorous activity per week now has backing from both observational and genetic evidence.
As such: There is no support here for pushing patients past that range for ocular benefit.