A recent study published in The Ocular Surface investigated the relationship between dry eye disease (DED) and the Mediterranean diet on a population-wide scale.
Give me some background first.
The study of connections between nutrition and diseases has increased in recent years, with the Mediterranean diet being a large focal point.
Antioxidant, antithrombotic, and anti-inflammatory properties of the diet have been identified as well as potential links to longevity, reduced risk of cardiovascular disease, and general health status improvement.
And the connection to this study?
The researchers hypothesized that the anti-inflammatory nature of the Mediterranean diet could possibly aid ocular surface inflammation that is consistent with dry eye disease (DED).
Now talk about it.
Investigators pulled from a population-based cohort study called the “Dutch Lifelines Cohort,” composed of 167,729 people living in the Netherlands and designed to track various factors related to health and genetics.
Participants self-enrolled or were selected via general practitioners between 2006 and 2013, and will be followed for 30 years in total. Elements of the study include general assessments with physical tests and periodic follow-up questionnaires.
What else?
With information on the participants’ diet and DED, descriptive statistics and regressions were then utilized to determine the relationship between the two variables.
How did they get information about DED?
Information pertaining to dry eye was collected during the second general assessment (administered between 2014 and 2017), when the participants were given the Women’s Health Study (WHS) dry eye questionnaire that consists of three questions:
- “How often do your eyes feel dry (not wet enough)?
- “How often do your eyes feel irritated?”
- “Have you ever received a diagnosis of dry eye?”
A participant is considered to have “WHS-defined DED” either when they select “Yes” to having been diagnosed or when they exhibit consistent eye drying and irritation.
How did they measure nutrition?
Typical patterns in participants’ diet regime and micronutrient intake were identified through food frequency questionnaires developed by Wageningen University and Research.
Adherence to the Mediterranean diet was determined by the modified Mediterranean Diet Score (mMDS), which assesses dietary intake to give an eventual score between 0-9.
As the Dutch diet varies from the Mediterranean diet, a secondary score “using pre-defined cut-offs was also used to assessed absolute adherence to a Mediterranean diet (aMDS).”
Findings?
This cohort showcased a reversal of the researchers’ hypothesis, where increased mMDS actually was somewhat associated with a greater risk of DED.
The same relationship was determined when looking at symptomatic DED—reducing the likelihood that it could be caused by changed behaviors post diagnoses.
How do past studies factor into this?
This was the first large epidemiological study investigating a potential correlation between DED and the Mediterranean diet. However, the findings are consistent with a smaller study of male participants, which also identified higher levels of DED following an increased consumption of the Mediterranean diet. .
Expert opinion?
Per the study authors, “there appears to be no large population-wide protective effect against DED of adherence to a Mediterranean Diet in the general population, despite its known anti-inflammatory effects.”
Limitations?
The study being cross-sectional limited the possibility to show causation. However, reverse causality was investigated when researchers removed DED to look at symptomatic dry eye.
Another notable limitation was that many of the questionnaires were self-reported, opening the door to potential biases.
Lastly, while the WHS dry eye questionnaire is the most widely used and has been clinically validated, the lack of actual clinical tests does introduce a limitation.
Take home.
Despite the Mediterranean diet’s well known association with various health benefits, including its anti-inflammatory properties, the study suggests that its adherence may not offer the anticipated protection for DED.
Further research with specific clinical trials are needed to fully explore the relationship.