Sodium levels linked to glaucoma risk

Glaucoma News: Recent research from a team of international scientists has uncovered a possible link between dietary sodium intake and the risk of developing glaucoma, a leading cause of blindness worldwide. This Glaucoma News report highlights key findings of the study, which involved participants from the United Kingdom and provides insights into how excessive sodium consumption could potentially affect eye health.


Sodium levels linked to glaucoma risk

The Research Behind the Findings
The study was conducted by a group of researchers from prominent institutions, including the University College London (UCL), Moorfields Eye Hospital, the University of Cambridge, and the University of Edinburgh, among others. They explored the relationship between urinary sodium excretion, a reliable indicator of dietary salt intake, and various eye health indicators like intraocular pressure (IOP), which is closely linked to glaucoma. The study used data from the UK Biobank, a large-scale population-based study, to investigate these associations.
 
More than 103,000 individuals, with an average age of 57 years, participated in the study. The researchers measured the participants’ sodium excretion levels using urine samples and examined their eye health, including their IOP, thickness of the macular retinal nerve fiber layer (mRNFL), and prevalence of glaucoma. In addition, they took into account the participants’ genetic predisposition to glaucoma by using a polygenic risk score that involved over 2,000 genetic variants.
 
Study Findings
The results showed a clear link between higher levels of sodium excretion and increased intraocular pressure. A one standard deviation rise in the sodium-to-creatinine ratio in urine was associated with a significant increase in IOP. Participants with the highest sodium levels had, on average, a 0.45 mmHg higher IOP than those with the lowest levels. This increase in IOP is particularly concerning because elevated intraocular pressure is a key risk factor for glaucoma.
 
Moreover, individuals with the highest sodium excretion levels were 30% more likely to have glaucoma compared to those with the lowest sodium excretion. Importantly, the study found that this association was stronger in participants who had a higher genetic risk for glaucoma. Those in the highest genetic risk category experienced the largest increase in glaucoma prevalence when their sodium intake was high.
 
However, it is worth noting that despite the link between sodium excretion and IOP, the researchers did not find a direct association between sodium levels and the thickness of the mRNFL or the ganglion cell-inner plexiform layer (GCIPL), two other important markers of eye health.
 
Salt Intake and Its Impact on Eye Pressure
One of the key explanations offered by the researchers is that high sodium intake leads to water retention and increased blood volume. This, in turn, can raise blood pressure and possibly affect eye pressure. Blood pressure has already been shown in various studies to have a direct effec t on intraocular pressure, which may explain the results observed in this study.
 
Previous research had already established the link between high blood pressure and glaucoma. However, this study highlights a new potential pathway - through dietary salt intake - by which people might be increasing their risk of glaucoma. High salt consumption could lead to fluid retention not only in the blood vessels but also within the eyes, thereby increasing the pressure that damages the optic nerve over time.
 
Genetic Factors Play a Role
The study also emphasized that the relationship between sodium intake and glaucoma risk may depend on a person's genetic predisposition. The researchers observed that individuals with a high polygenic risk score for glaucoma were more vulnerable to the adverse effects of sodium on eye health. This finding suggests that those with a family history of glaucoma should be particularly cautious about their salt intake.
 
Interestingly, this connection between genes and lifestyle factors, such as diet, supports the emerging field of precision nutrition. In the future, it may be possible to tailor dietary recommendations for individuals based on their genetic risk factors for certain conditions, including glaucoma.
 
Broader Implications for Public Health
Glaucoma is a complex disease with multiple contributing factors, including age, ethnicity, genetics, and environmental influences. With over 70 million people affected by glaucoma globally, and numbers expected to rise, identifying modifiable risk factors like dietary salt intake is crucial for disease prevention and management.
 
Excessive sodium consumption is already known to cause cardiovascular problems, such as high blood pressure, and now this study suggests it could also be harming eye health. Most health organizations, including the World Health Organization (WHO), recommend limiting sodium intake to less than 2,000 milligrams per day (or less than 5 grams of salt), yet the average sodium intake in many populations exceeds this recommendation.
 
Study Limitations and Future Research
While this study provides valuable insights, it does have some limitations. Since the data was cross-sectional, it only shows associations and cannot prove a direct cause-and-effect relationship between sodium intake and glaucoma. Longitudinal studies are needed to confirm whether reducing sodium intake can lower intraocular pressure and reduce the risk of glaucoma development.
 
Additionally, the researchers used urinary sodium excretion as a proxy for dietary sodium intake. Although this is considered an accurate method, it may not perfectly reflect long-term dietary habits or capture all fluctuations in salt consumption.
 
Finally, most of the study participants were of European descent, so the findings may not necessarily apply to other ethnic groups, especially those with higher rates of salt-sensitive hypertension.
 
Conclusion
This study sheds new light on how dietary habits, particularly sodium intake, might influence eye health and glaucoma risk. The results suggest that controlling salt intake could be an effective strategy for managing intraocular pressure and reducing the likelihood of glaucoma, especially in individuals who are genetically predisposed to the condition.
 
For those with a family history of glaucoma or other risk factors, making dietary changes might be a simple but impactful step towards protecting their vision. However, further research is needed to confirm these findings and to explore the possibility of developing personalized dietary recommendations for glaucoma prevention.
 
The study findings were published in the peer-reviewed journal: Ophthalmology Glaucoma.
https://www.sciencedirect.com/science/article/pii/S2589419624000747
 
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