In a recent study published in Transitional Vision Science and Technology, researchers investigated the causal effects of physical activity (PA) on the risk of developing senile cataracts (SC).
Give me some background first.
Cataracts are one of the most common causes of vision loss in older individuals, affecting an estimated 95 million globally.
Symptoms can include:
- Cloudy or blurry vision
- Colors appearing faded
- Trouble seeing at night
- Lamps, sunlight, or headlights appearing too bright
- Seeing a halo around lights
- Seeing double vision
- Needing to change the prescription of glasses or contacts often
In relation to this research: SC—also referred to as age-related cataracts—commonly occurs due to aging.
Now, talk about the study.
Investigators utilized a bidirectional two-sample Mendelian randomization (MR) approach for their analysis.
Several methods were used in their analyses, including:
- Primary analysis
- Inverse variance weighted method
- Secondary analyses
- MR-Egger regression
- MR-PRESSO
- Cochran's Q statistic
Note: Causal estimates were presented as odds ratios (ORs) with 95% confidence intervals (CIs).
What data was used in the study?
Investigators utilized PA summary statistics from a genomewide association study (GWAS) within the United Kingdom (UK) Biobank cohort.
The study involved an estimated 400,000 individuals aged 40 to 69.
A second GWAS study was also mentioned that involved 377,234 individuals of European descent.
Further: The data source for SC was obtained from a dataset on FinnGen, which included 406,781 individuals of European ancestry comprising:
- 65,235 cases
- 341,546 controls
Findings?
The following were associated with decreased risk of SC:
- Genetically predicted moderate PA ≥ 10 min/wk
- OR = 0.765, 95% CI = 0.627–0.936, P = 8.73E-03
- Vigorous PA ≥ 10 min/wk
- OR = 0.691, 95% CI = 0.521–0.917, P = 1.04E-02
- Moderate-to-vigorous PA levels
- OR = 0.552, 95% CI = 0.369–0.823, P = 3.75E-03
- Overall acceleration average
- OR = 0.952, 95% CI = 0.926–0.978, P = 3.80E-04
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Additionally:
- Walking ≥ 10 min/wk had no significant correlation with decreased risk of SC
- OR = 0.972, 95% CI = 0.741–1.275, P = 8.36E-01
- Reverse MR analysis showed no reversal causality from SC to PA except for walking ≥ 10 min/wk
- OR = 0.951, 95% CI = 0.923–0.979, P = 7.30E-04
Now interpret this data.
The investigators hypothesized that the potential preventative effect that PA had on SC could be due to several factors:
- Alleviate oxidative stress
- The lens is highly impressionable to oxidative damage, which can lead to opacities.
- The authors stated that PA may alleviate oxidative stress by activating antioxidant enzymes.
- Enhance the formation of high-density lipoprotein (HDL)
- HDL is vital in transporting lipophilic antioxidants.
- Elevated levels of HDL may facilitate the transport of more antioxidants from the plasma to the lens, which can prevent oxidative damage and inflammation in the lens.
- Inhibit concentrations of circulating C-reactive protein
- C-reactive protein is an inflammatory marker associated with a higher SC risk.
- Manage certain health aspects
Limitations?
Bidirectional MR was based on the GWAS data focusing on populations of European ancestry.
What this means: The broader application of the findings to other populations who may have different causes of visual impairment could be limited.
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The research did not reveal the relationship between PA and specific subtypes of SC, which could present with different clinical symptoms.
Additionally, the study can not be replicated because it relied on the GWAS data and a lack of validation sample,
Meaning: This could limit the interpretation of the findings.
For a full overview of the limitations, refer to the study.
Expert opinion?
The authors recommended that future studies test their findings on a more diverse population, recruit more young SC samples, and use more inclusive definitions to identify SC cases to obtain a more accurate incidence estimate.
Take home.
Moderate and vigorous intensity PA with a higher frequency and longer duration may be effective for SC management and prevention, they concluded.