Nutrition of patients with primary open-angle glaucoma

INTRODUCTION

Glaucoma, according to the European Glaucoma Society and the American Academy of Ophthalmology, is a group of chronic and progressive diseases of the eye, which are characterised by morphological changes in the structure of the optic nerve, the ganglion cell layer and retinal nerve fibre layer [1, 2]. Primary glaucoma, which accounts for 80-90% of all cases of the disease, is not associated with other ocular diseases and congenital abnormalities [3]. From the pathomechanical point of view, glaucoma is defined as a multifactorial neurodegenerative disorder with progressive loss of retinal ganglion cells and changes in the visual field [4, 5].

Primary open-angle glaucoma (POAG) affects every race regardless of social status and place of residence. It is estimated that currently, glaucoma affects approximately 70 million patients, and 14% of this group are end-stage glaucoma cases. Predictions suggest that the number of glaucoma patients will increase to 118,8 million by 2040. It is emphasized that every year about 2,4 million people globally lose their sight due to glaucoma. In Poland, the problem of glaucoma concerns 750-800 thousand people, of which only about 16% are subject to permanent treatment [6].

The etiopathogenesis of glaucoma, despite careful research, is unclear. Widely acknowledged factors contributing to its development and progression are elevated intraocular pressure (IOP) and impaired blood supply to the optic nerve and retina [7].

In addition, apart from elevated IOP values, research mentions other glaucoma risk factors such as age over 35, ethnicity (African Americans) and family history of the disease.

Moreover, correlation between POAG and diabetes, dyslipidaemia, thinner cornea and high axial myopia has been reported [8]. In contrast, there is inconclusive data regarding the association of glaucoma with gender and cardiovascular disease, including heart disease, cardiomyopathies, abnormal blood pressure, nocturnal hypotension, history of stroke, and Raynaud’s disease [8].

Lack of complete understanding of the pathogenesis of the disease, along with limited efficacy of conservative and surgical treatments, has led to the exploration of other factors associated with the development of glaucoma, including the potential role of health and diet-related habits.

Currently, only a few studies indicate that inadequate nutrition and alcohol consumption may contribute significantly to the onset and progression of glaucoma [9, 10]. However, the results of these studies are inconclusive, often conflicting as well as controversial [3, 11, 12].

The aim of the study is to assess the nutrition of patients with glaucoma and the relationship between the adopted nutrition models, the degree of overweight and obesity, and primary open-angle glaucoma.

MATERIAL AND METHODS

The study group was recruited among patients who were admitted because of POAG to the Department of Ophthalmology and Visual Rehabilitation, University Hospital WAM, Central Veteran Hospital in Lodz, Medical University of Lodz, Poland. The requirement for inclusion of subjects in the study group with POAG was a diagnosis of POAG by an ophthalmologist in accordance with the applicable criteria for diagnosing the disease (documented raised intraocular pressure, documented changes in the optic disc correlating with changes in visual field) [13, 14].

The control group was recruited among patients admitted to the aforementioned Department of Ophthalmology for different reasons, with no past medical history of glaucoma or family history of glaucoma. In total, 625 adults (age: 46-96 years) were enrolled in the prospective study. The study group comprised 312 subjects diagnosed with POAG, including 238 women (W) – 76% (476 eyes) and 74 men (M) – 24% (148 eyes). Control group consisted of 313 subjects with no glaucoma diagnosis – including 202 W – 64%, (404 eyes) and 111 M – 36% (222 eyes). General data, including anthropometric indices and body mass index (BMI) [kg/m²], was collected during the interview with the patient including original questionnaire. In the study following BMI values interpretation was applied: normal – BMI 18.5-24.9, overweight – BMI 25.0-29.9, and obesity – BMI ≥ 30 [11].

Nutritional value and composition of consumed meals were also assessed. Study participants were surveyed on their diet (including alcohol consumption) on the day preceding the survey – they gave exact information about each meal consumed that day, including its components and amount. The grammage of meals and selected components of the subjects’ diet were determined comparatively based on photographs included in the album of products and dishes – National Food and Nutrition Institute Publishing House, Warsaw 2000 [15]. The data were later introduced into the Computer Program – Diet 2.0 [16], which calculated the values of the analysed nutrients and ingredients. The daily nutrition of the study subjects was later analysed based on the Questionnaire obtained from this Computer Program.

Data regarding the ophthalmological diagnosis as well as comorbidities (including diabetes, hypertension, cardiovascular diseases) was obtained from the patient’s medical records based on the consent of the Bioethics Committee of the Medical University of Lodz (approval number: RNN/35/11/KB).

As far as statistical analysis is concerned, in order to compare the mean values of measurable variables in two groups, the Mann-Whitney test was used, while in order to compare the frequency of specific categories of non-measurable characteristics in two groups, following tests were used: χ² test of independence and the χ² test of independence with Yates correction, Fischer’s exact test.

Statistical analysis was performed using the Statistica 13,0 statistical package, with significance level p < 0.05.

RESULTS

Obesity (BMI > 30) was found to be significantly more prevalent among subjects with POAG, regardless of gender (p < 0.000). The number of women with normal weight (BMI 18.5-24.9) was significantly lower in the group with glaucoma than in the control group (29,4% vs. 56,4%; p < 0.000). Women with glaucoma were characterised by higher body weight and higher BMI values [kg/m²] than control group women (p < 0.000).

Moreover, the group of men with glaucoma seemed to exhibit higher body weight and higher BMI values [kg/m²] than men in the control group, but the difference was statistically insignificant (p > 0.05; Tables I and II).

The distribution of the number of meals consumed per day was statistically significantly different between the groups (p = 0.001). The highest percentage of subjects (72.0%) ate 3 meals per day, more frequently in the group with glaucoma, but the results were statistically significant only for women (p = 0.000; Tables III and IV).

Daily diet of men with glaucoma did not generally differ in the content of nutritional components in comparison to the control group (p > 0.683). However, the meals of men with glaucoma were found to be richer in saturated (p = 0.001) and unsaturated fats (p = 0.023) as well as cholesterol (p = 0.039) compared to the dishes consumed by men in the control group. It seems interesting that the number of subjects consuming alcoholic beverages was significantly lower in the study group (p = 0.000). Men more frequently than women consumed alcoholic beverages in both groups, respectively: POAG group: M 40.5% vs. W 24.4% (p = 0.007) and control group: M 50,4% vs. W 38,1% (p = 0.035).

On the other hand, analysis of the components of meals consumed by women with glaucoma showed significant differences compared to women in the control group as to both their number and “size” (grammage) of ingredients (p < 0.02). The results showed that women with POAG ate statistically more frequently 3 meals per day, consuming higher amount of ingredients such as cholesterol and animal and vegetable proteins. Moreover, women with glaucoma ingested less water (p = 0.000). Remarkably, the volume of alcohol intake was higher in women with glaucoma (p < 0.014; Tables V, VI, and VII).

It was found that dietary restrictions were not followed by 76% of the subjects. The mentioned percentage was similar in both groups, regardless of gender (p > 0.05). However, results regarding this topic lacked statistical significance.

The most frequently applied dietary restriction in both groups concerned the intake of simple sugars, which seemed more prevalent in the group of patients suffering from glaucoma in both gender groups, but the difference was statistically insignificant (p > 0.05), both among men (14.9% vs. 11.7%) and women (8.8% vs. 9.9%). Furthermore, apparently, the least followed guideline was related to fat-restricted diet in both groups (p > 0.05).

Regarding the POAG group, men were more likely to adhere to dietary restrictions than women (M 25.7% vs. W 23.9%). Different trend was observed in the group of subjects without glaucoma, where women were more likely to use dietary restrictions (M 17.1% vs. W 27.2%; Tables VIII and IX).

Moreover, for the glaucoma group, among subjects following dietary restrictions (n = 76), less frequent prevalence of overweight (23.1%) and obesity (19.0%) was observed compared to non-restrictors (76.9% and 81.1%, respectively).

In the comparative analysis between the groups, a higher proportion of normal weight was noted among individuals following dietary restrictions in the study group (31.9% vs. 24.5%; Table X).

Total daily energy values consumed by the subjects with glaucoma were higher than in the control group, although statistically significant values were observed only among women with glaucoma (p < 0.000).

It was demonstrated that in both study and control group, the energy obtained from carbohydrates constituted the highest percentage of total daily caloric intake for both genders (p > 0.05). Interestingly, it was shown that in the group of people with glaucoma these values were significantly lower, both among men (p = 0.016) and women (p = 0.006).

As far as the level of energy obtained from fat consumption is concerned, it was higher among both men (p = 0.016) and women with glaucoma (p = 0.04) than in the control group.

Remarkably, the percentage of energy obtained from alcohol consumption was higher among subjects with glaucoma, with statistically significant differences observed only among women (p = 0.004; Table XI).

DISCUSSION

According to World Health Organization, health behaviour is the entirety of a person’s habits, customs and attitudes related to health of an individual or the whole society. Health-related behaviours are actions and activities undertaken by humans to improve health or reduce the impact of disease [17].

It has been widely acknowledged that improper health behaviours, including inappropriate dietary habits and alcohol abuse, constitute a group of important risk factors for the occurrence of chronic diseases [18-20]. It is evident that daily diet influences adequate human development and functioning and should contain the right proportions of components including protein, carbohydrates, vitamins, micro- and macroelements as well as saturated and unsaturated fats. In this context, the impact of incorrect health behaviours, including inappropriate diet, on the occurrence of chronic diseases has also been raised [21, 22].

Furthermore, it is widely recognized that inadequate diet as well as consequent overweight and obesity can increase incidence of certain chronic conditions, including POAG [23-25]. According to a number of researchers, consumption of alcohol may contribute to increased intraocular pressure and progression of glaucoma [26-28]. In previous studies conducted by this article’s authors, very low physical activity was found to correlate with higher incidence of glaucoma and faster progression of the disease [28-31].

In this study, we demonstrated that the dietary habits of people with glaucoma significantly deviate from the recommendations of the public health schemes. It was proven that the overwhelming number of the subjects did not follow any dietary restrictions.

Ramdas et al. [32] identified that overweight and obesity were significantly more prevalent among people treated for POAG, which is consistent with this study’s finding that POAG group was characterised by higher body weight and BMI index values. Additionally, according to the authors cited above, each BMI unit reduction results in decrease of the risk of developing glaucoma by 7% [32].

To sum up, taking into account the conclusions of former papers, it can be assumed that the results obtained from this study should be regarded as a strong argument indicating that poor diet and the subsequent overweight and obesity constitute a major risk factor for glaucoma.

Evidently, the primary role of nutrition is to satisfy the qualitative and quantitative demand for nutrients. Daily diet should provide sufficient energy for the proper functioning of the human body, taking into account age, gender, physical activity and environmental temperature. According to widely recognised recommendations, the daily energy requirements of an adult human being should not exceed 2,300 kcal for men and 1,900 kcal for women.

Ideal diet is well supplied with vitamins and minerals. An exceptionally frequent dietary mistake is insufficient intake of vegetables and fruit, which leads to vitamin and mineral deficiencies [33]. Furthermore, a preferred daily diet also includes low-glycaemic index carbohydrate meals, well-known to be an important source of fibre. A varied daily menu is widely recognised to help maintain a good balance between the above-mentioned components.

It has been established that 57% of the daily energy intake should come from carbohydrates, 20-30% from fats and 13-15% from protein. As mentioned, 50% of the protein in the daily ration should be animal protein. 30% of fats should be from vegetable source [34-36]. It is also considered essential to consume fats rich in omega-3 fatty acids due to their antineoplastic effects, reduction of the risk of heart attacks as well as because of their beneficial effects on cognitive function [37]. It is also necessary to drink an adequate amount of water, between 30 and 45 ml/ kg/b.w. per day [38-40].

Literature underlines the significant impact of the components of the daily diet on the state of the organ of vision [33]. In our own study, it was revealed that the daily caloric energy intake of people with glaucoma significantly exceeded the recommended standards. The mean value of total daily energy obtained from meals in the glaucoma group was 3,442 kcal and was on average higher by approximately 400 kcal than among glaucoma-free subjects. Remarkably, the diet of the glaucoma subjects was richer in all components of the daily diet, except water. It also seems interesting that the frequency of alcohol ingestion was lower than in control group but the amount of alcohol consumed was higher among glaucoma group especially in women.

Coleman and other authors claim that the presence of adequate levels of vitamins in diet prevents glaucoma [40]. Insufficient level of vitamins B₆ and B₁₂, as suggested by Turgut et al., is a determinant of glaucoma occurrence [41]. Furthermore, consumption of meals containing adequate amounts of vitamins: A, B, C, E, carotene, beta carotene, selenium, and zinc may play a role in preventing the progression of ganglion cell damage in individuals with glaucoma [42-44]. Our results showed that diet of people with POAG contained more vitamins: A, β-carotene, C, D as well as group B in comparison to control group. Probably, it can be linked with the excessive food supply also indicated by high prevalence of overweight and obesity in glaucoma group.

On the other hand, it has been reported that diet rich in magnesium, copper as well as selenium, zinc and B-group vitamins decreases intraocular pressure values by 13% in the period of 40 weeks from the beginning of their supplementation [45, 46]. Other authors also make similar suggestions regarding the role of zinc and selenium in glaucoma therapy [47]. In his work, Johnson suggests that magnesium is one of the most important minerals and its presence in the diet influences the processes of synthesis and breakdown of energy-rich compounds. In addition, its dietary deficiency significantly increases blood cholesterol levels [48]. Aydin et al. described the role of magnesium in improving blood flow in the ocular arteries [49].

As far as intake level of macro and microelements is concerned, similarly to vitamins, its higher consumption in glaucoma group is likely due to increased amount of consumed food compared to control group.

Some authors imply that consumption of vegetables exerts an important protective effect against the development of glaucoma [50, 51].

In turn, the impact of ingesting excessive amounts of fluids on intraocular pressure values is inconclusive. Some studies have demonstrated that drinking 1,000 ml of water raises intraocular pressure by more than 30% [52-54].

Water drinking test, which evaluates the impact of single intake of a significant amount of water (typically 1,000 ml) on IOP, shows more significant increase of IOP values in POAG patients after the test compared to healthy subjects [55, 57]. Moreover, Susanna et al. showed that POAG patients with more progression in visual field test also had higher IOP rise after water drinking test [56].

However, we did not find in the available literature any articles considering general, long-lasting impact of water intake on glaucoma. Based on the various results obtained by other researchers, such studies should be conducted in order to better understand the subject [55-57]. Certain publications report the importance of alcohol consumption in the onset of glaucoma [58, 59]. Wise et al. suggest that alcohol intake is an important initiating factor in the development of glaucoma [60].

Other authors contradict this relationship, indicating that alcohol consumption lowers IOP by approximately 2 mmHg [61-63]. Data from our research showed that women in POAG group were characterised by higher alcohol in-take than control group.

CONCLUSIONS

Concluding from the obtained results, it can be observed that people with glaucoma in contrast to the general adult glaucoma-free population were characterized by:

Concluding the findings of this study, it is recommended to intensify the education of POAG patients in terms of proper diet and possibly other health-related behaviours. Such action may have a beneficial impact on the process of treatment, prevention, occurrence and modification of the course of POAG.

Apparently, further research is needed to determine the role of efficacy and safety of nutritional methods and nutritional supplementation in the treatment of glaucoma.

Lifestyle modification can delay the onset, and in some cases stop the disease progression by preventing visual disability and may allow to maintain social and occupational activity of people with POAG.