Dry Eye Disease and Dehydration

Overview

Can greater habitual water intake lower the risk of dry eye disease (DED)? Dry eye disease is a complex disease of the tear film and ocular surface. It causes discomfort, visual disturbance, and the risk of damage to the ocular surface. DED is a condition when a person’s tears aren’t able to provide lubrication for the eyes. It has a prevalence of 5% to 50% depending on the population and definition adopted. Dry eyes can occur if a person also doesn’t produce enough tears or only produces poor-quality tears.

Dry eye symptoms include eye pain and irritation. It can also cause a substantial reduction in a person’s general well-being and quality of life. Normal life activities such as reading, watching television, and driving, are also often affected. Furthermore, DED also causes an economic and financial burden with an estimated annual cost of USD 3.84 billion in the US alone. The disease is even more difficult to treat once the stops are already established. This study’s goal is to uncover modifiable risk factors and interventions that may prevent the development of DED.

Study Methods

There were a total of 51,551 participants included from the population-based Lifelines cohort in this cross-sectional association study. DED was assessed using the Women’s Health Study (WHS) dry eye questionnaire. Water intake was calculated from food frequency questionnaires. Logistic regressions were used to analyze the relationship between DED and water intake or 24-h urine volume, corrected for age, sex, body mass index, physical activity, smoking status, education, income, 48 comorbidities, and 15 medication groups. The main outcome measure was WHS-defined DED. Highly symptomatic dry eye and clinical diagnosis of DED were secondary outcomes.

Assessment of DED

This study used the Women’s Health Study (WHS) dry eye questionnaire to assess DED at assessment. This questionnaire is the most frequently used tool when assessing DED status in population-based studies. The instrument has been validated against a standardized clinical exam and has a similar sensitivity and specificity as a 16-item survey. The WHS questionnaire consists of the following three questions:

(1) “How often do your eyes feel dry (not wet enough)?”

(2) “How often do your eyes feel irritated?”

(3) “Have you ever received a diagnosis of dry eye?”

Questions 1 and 2 have possible answers of: “Never,” “Sometimes,” “Often,” and “Constantly.” Question 3 has possible answers of: “Yes,” “No,” and “I don’t know.” WHS-defined DED was the main outcome measure of this study. WHS-defined DED requires either a self-reported clinical diagnosis of DED or “highly symptomatic dry eye”.

Assessment of water intake

A 110-item semi-quantitative food frequency questionnaire (FFQ) assessing dietary consumption over the previous month was specially developed for the Lifelines cohort study. The FFQ was administered in four parts, with an assessment of major food groups at baseline and three follow-up questionnaires investigating micronutrients.

Assessment of possible confounding factors

At baseline, participants were asked to: “…indicate which of the following disorders you have or have had?” with a wide range of possible answers relating to cardiovascular, chronic pain, gastrointestinal, kidney and urinary, neurological, hematological, autoimmune, skin, and mental conditions. Additionally, subjects were asked to report, using free text, any other disorders that they have or have had.

At repeat visits, the participants were requested to provide information about the occurrence of new conditions since their last questionnaire. A specific questionnaire assessing ocular conditions and traits was also given to the participants at the same time as the DED assessment. Using this information, dichotomous variables were created for the occurrence of a broad range of diagnoses and conditions, as previously described in greater detail. 48 comorbidities were found associated with WHS-defined DED.

Results

In total, 9.1% of the population had WHS-defined DED. Higher water intake was associated with an increased prevalence of WHS-defined DED (OR: 1.011 per 100 ml/day, 95% CI: 1.004–1.017, p = 0.003).

After excluding those with a clinical diagnosis, greater water intake was still tied to an increased risk of having DED symptoms (OR: 1.010 per 100 ml/day, 95% CI: 1.006–1.015, p < 0.001). Higher 24-h urine volumes were also associated with a higher risk of WHS-defined DED (OR: 1.010 per 100 ml/day, 95% CI: 1.005–1.015, p < 0.001).

The prevalence of WHS- defined DED was 9.1%, with females more likely to have DED than men. The mean total water intake was 2491 ml/day with beverage water contributing 62% of the total water consumed. The rest was made up of food water (28%) and metabolic water (10%). On average, males had a higher intake of water from all sources than females.

Females had an increase in the prevalence of WHS-defined DED with increasing water intake, with the 1st quintile (1684 ml/day) having a prevalence of 11.1% compared with 13.4% in the 5th quintile (3257 ml/day). In the male population, the prevalence of WHS-defined DED was 4.7% in the 1st quintile (1824 ml/day) and 5.3% in the 5th quintile (3539 ml/day).

Conclusion

The study shows that higher water intake was not tied to a reduced risk of DED. Rather, it was associated with a modestly increased risk of DED. Interventional studies are needed to fully understand the effect of water intake on DED, but this study found no evidence that greater water intake is beneficial for DED.

While greater water intake has been associated with health benefits in other general populations, such as a lower risk of nonalcoholic fatty liver disease and chronic kidney disease, this large epidemiological study did not find it to be associated with a reduced risk of having DED.

The findings contradicted the hypothesis. In fact, both a higher self-reported water intake and a greater measured 24-h urine volume were tied to an increased prevalence of DED. The same relationship was found when beverage water and food water were assessed separately. However, there was no significant difference in DED prevalence in the 5th and 1st age decade-specific quintiles of water intake in either sex after correcting for comorbidities and medications.

The European Food Safety Authority recommends a daily intake of food and beverage water of 2.0 L/day for females and 2.5 L/day for males, but no upper limit was defined (EFSA Panel on Dietetic Products, 2010). This includes water from all food and beverage sources but excludes metabolic water.

In this study, when excluding metabolic water, 74.5% of males and 39.8% of females consumed less than these recommendations. Using this cutoff in a sensitivity analysis, the results were similar to that of the analyses presented in the current study, with water intake above the cut-off being significantly associated with more WHS-defined DED in all models.

Dry Eye Disease and Dehydration