Influence of Dietary Seafood on the Prevention of Ocular Disorders: A Clinical Analysis

Abstract

Age-related macular degeneration, retinal dysfunction, dry eye syndromes, cataract formation, and the prevalence of other vision defects are directly related to nutrients in the diet. People consuming seafood are less prone to several vision disorders. The present study was designed to validate the view. In this study, 712 visitors to tertiary eye care for eye check-ups were interviewed using a standard questionnaire, and from them, 264 persons were identified with some ocular defects. The identified cases were further screened based on their dietary habits with seafood. The isolated cases were clinically examined, and the development of ocular defects such as macular edema, optic neuropathy, myopia, double vision, dry eye syndrome, and color blindness was recorded. The results show that the respondents taking one or another type of three fishes regularly have a low impact on visual disorders. Respondents with fish intake above 500 g/week were less affected by all five ocular disabilities tested when compared with occasional users. Among the total respondents, the percentage of visual defects was seen in 62.12% in seafood users, but among the non-seafood users, the presence of visual defects was 89.6%. Statistical analysis using the Pearson population correlation coefficient, ρ (rho), further confirmed the relationship between eye wellness and a seafood diet. The omega-3 fatty acids linked with vision were also high in the fish consumed by the people. This study confirms that a regular seafood diet is good for eye health and can prevent the epidemics of several eye diseases. As fish intake contains a good amount of long-chain polyunsaturated omega-3 fatty acids, people who consume fish in their diet are less susceptible to advanced macular degeneration and other vision impairments responsible for age-related blindness.

Main article text

INTRODUCTION

Diet plays a vital role in keeping the ocular system proficient and reducing the incidence of disorders ( Lawrenson and Downie, 2019). A well-balanced, healthy diet maintains wholesome health and reduces vision impairments. A diet enriched with antioxidants, including essential fatty acids such as omega-3, vitamins A and C, carotenoid pigments such as lycopene, lutein, and zeaxanthin, and minerals such as zinc, supports good vision and reduces certain vision defects ( Mrowicka et al., 2022). Omega-3 fatty acids are “healthy fats” promoting good heart health, reducing triglycerides, protecting against autoimmune disorders, and preventing oxidative stress associated with eye disorders. The dietary intake of fish supplies a good amount of omega-3 fatty acids, vitamins, and minerals to prevent meibomian gland dysfunction, macular degeneration, and vision impairment ( Braakhuis et al., 2019). The macular region is a part of the retina, the vision center, and its degeneration causes macular edema or swelling that ends in blurry vision due to blood vessels leak. Regular fish intake supplies omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), vitamins, and minerals that help to keep the eyes healthy and vision protected ( Zhang and Downie, 2019). Dietary sources of omega-3 help in easy absorption than synthetic drugs ( Ponnampalam et al., 2021).

Healthy practices such as exercise, a nutritious diet with antioxidants, vitamins, and minerals, and quitting smoking protect the ocular system from many disorders ( Matsumura et al., 2022). A nutritional diet prevents defects related to the optic nerve, helps overcome problems related to visual acuity and image contrast, and enhances optic neural communication with the brain. Optic neuropathy indicates damage to the optic nerve that transfers visual information from the eyes to the brain in your eye and causes visual impairment. Nutritional optic neuropathy impairs mitochondrial function, electron transport, ATP synthesis, and vision ( Roda et al., 2020). Optic neural disorders can be remediated by supplementing with vitamins ( Chandrinos et al., 2023). Omega-3 fatty acids are essential for cardiac health, brain functions, and the endocrine system as they are good antioxidants. Omega-3 fatty acids, EPA, and DHA are essential for cellular function in the retina. Dietary supplementation is the only source for providing these essential fatty acids. Socio-demographic background also influences vision-related issues ( Rajput and Pawar, 2018; Wong et al., 2020).

A study using a sample of 32,000 female respondents proved that dietary intake of fish with omega-3 fats reduced the risk of dry eye syndrome by 17% compared to non-seafood consumers ( Miljanović et al., 2005). Dry eye syndrome involves inadequate secretion of tears that lubricate the eyes and leads to stinging, burning sensations, inflammation, and damage to the eye’s surface. Fish intake supplies omega-3-fats that are vital for the functioning of meibomian glands and reduce the risk of dry eye symptoms ( Giannaccare et al., 2019). Omega-3 fats protect against age-related macular degeneration (AMD) and other retinal defects ( Titiyal et al., 2018). The retina, especially the macula, is prone to high oxidative stress because of heavy production of free radicals. The excessive free radicals induce oxidative stress in DNA and damage protein synthesis inside the retinal cells. Therefore, antioxidant provision is essential to fight against free radicals to protect the retina from cellular damage ( Monés et al., 2021). The presence of two carotenoid pigments, lutein and zeaxanthin, protects the retina from oxidative stress and macular degeneration ( Eisenhauer et al., 2017). Eye disorders like myopia (near-sightedness), color blindness (color differentiation inability), and double vision (misalignment of one or both eyes) stay away from regular seafood consumers. Lutein and zeaxanthin pigments protect cells in the macular area by absorbing excess blue and ultraviolet light and neutralizing free radicals. Seafood is a good source of lutein and zeaxanthin ( Buscemi et al., 2018). Ocular defects are reduced if fish is added to the diet twice a week, along with some fruits and vegetables ( Laíns et al., 2022). The polyunsaturated fatty acids (PUFAs) in seafood are responsible for the progression of diabetic microangiopathy ( Shah et al., 2022). Against this background, the present study was designed to confirm the relationship between seafood (fish) diet and ocular wellbeing.

MATERIALS AND METHODS

To trace the relationship between the nutrient content, particularly fatty acid contents in the seafood diet, and the wellness of the eyes, an ophthalmic health survey and clinical examination were conducted as per WHO guidelines using visitors to a tertiary care eye hospital in South India. A standard questionnaire was administered to 712 respondents from the coastal area and adjacent villages who visited the hospital for general eye check-ups. The respondents were of both sexes and were aged 15-70 years. Among them, 264 respondents were identified with some ocular issues, and 448 had no major ocular-related problems. The identified cases were further grouped on the basis of their dietary habit. Of them, 164 cases were consuming seafood regularly or occasionally from their childhood and 100 were not consuming any seafood. The seafood consumers were further grouped based on the quantity of seafood they consumed daily and were examined clinically with the help of ophthalmic doctors after approval by the ethics committees of the Agarwal Eye Hospital, Tirunelveli [ethical approval numbers were 3215KY009 and No. 04 (2023)]. As per the dietary uptake of seafood, the respondents were divided into five groups. (i) Respondents consuming seafood—fish diet above 500 g per week. (ii) Respondents consuming 300-500 g of seafood in their food every week. (iii) Respondents consuming <200 g of seafood per week. (iv) Respondents consuming seafood occasionally. (v) Respondents who do not consume any seafood. Among the seafood users, the incidence of vision problems was 62.12%. However, among the non-seafood users, the incidence of vision problems was 89.6%. The 164 seafood consumers under four groups were further examined for five major types of optic defects. The prevalence of chosen optic defects included macular edema (30 patients, 30 eyes), optic neuropathy (30 patients, 30 eyes), myopia (30 patients, 60 eyes), double vision (14 patients, 28 eyes), dry eye syndrome (30 patients, 30 eyes), and color blindness (30 patient, 30 eyes). The statistical relationship between the five reported eye ailments and food habits was traced using Pearson’s correlation coefficient.

The respondents’ home towns are coastal and nearby places, where the people consume the identified fish varieties from their childhood as they are available throughout the year and are cheap. The prime fish varieties include sardine species ( Sardinella dayi, Sardinella fimricata, and Sardinella longiceps) belonging to the family Clupeidae. All three species are grouped as one sample. The second dietary component was the anchovies group, Stolephorus spp. belonging to the family Engraulidae. The third type of fish in their diet was the Indian mackerel Rastrelliger kanagurta, which belonged to the Scombridae family. Because fish intake correlates with defense against ocular disability, the nutrient content in the three major groups of fish in their diet was analyzed. Biochemical components, including protein, carbohydrate, fat, fiber, ash, and moisture, were estimated. Fatty acid contents in the three dietary fishes were estimated using standard protocols.

The fishes used in the respondents’ diets were collected from a fish landing center on the Tuticorin coast of South India for biochemical analysis. The fish were collected in December 2020. The weight range of sardines was 110-130 g, anchovies 25-35 g, and mackerels 100-304 g. For nutritional analysis, 100 g of flesh samples were taken from 15 representative samples from each group under aseptic conditions. The tissue samples were homogenized using a mechanical grinder and stored at −18°C for further analyses.

Assessment of nutritional components in the selected fishes

The moisture, protein, total lipids, carbohydrate, fiber, and ash content were estimated following the standard procedure. To estimate the fatty acid content in the fish groups, the flesh samples were homogenized using the chloroform:methanol mixture (2:1 v/v). The extracted fat was esterified with 1% sulfuric acid, and the prepared fatty acid methyl esters were subjected to gas chromatography analysis as described previously. Fatty acid peaks were detected using known standards ( Nollet, 2000).

Ocular deformities in respondents with seafood as their regular diet

A case–control study was designed to explore the relationship between seafood consumption and the incidence of major ophthalmic complications such as macular edema, optic neuropathy, myopia, double vision, dry eye syndrome, and color blindness. The respondents were examined clinically, their ocular disabilities were recorded, and the problems were correlated with their responses about their dietary seafood intake in the questionnaire. The statistical relationship between the five reported eye ailments and food habits was traced using Pearson’s correlation coefficient. The data were statistically analyzed for their correlation between the fish consumption frequencies and ophthalmic disease using IBM- SPSS Version 20.

RESULTS

Proximate composition

The proximate composition of the most commonly consumed fish showed a significant variation among the species ( P < 0.05) ( Table 1). In the Sardinella group of fish, the percentage of moisture, protein, fat, ash, carbohydrate, and fiber contents were 73.2 ± 0.41%, 23.5 ± 0.56%, 5.9 ± 0.42%, 1.4 ± 0.12%, 1.73 ± 0.32%, and 2.78 ± 0.1%, respectively. In anchovies, the percent occurrence of different proximate components such as moisture, protein, fat, ash, carbohydrate, and fiber contents were 67.4 ± 0.31%, 19.4 ± 0.31%, 4.6 ± 0.75%, 1.8 ± 0.14%, 1.47 ± 0.01%, and 2.3 ± 0.12%, respectively. In mackerel the presence of different proximate components such as moisture, protein, fat, ash, carbohydrate, and fiber contents were 74.33 ± 0.39%, 19.89 ± 0.07%, 10.89 ± 0.07%, 1.26 ± 0.14%, 0.29 ± 0.14%, and 1.82 ± 0.31%, respectively. Among the three groups of fish studied, the moisture content is high in mackerel (74.33 ± 0.39%) followed by sardines and anchovies 73.2 ± 0.41 and 67.4 ± 0.31%, respectively.

Table 1:

Proximate composition of selected fishes.

Proximate composition (%)	Sardines	Anchovies	Mackerel	Significance ( P < 0.05)
Moisture	73.2 ± 0.41	67.4 ± 0.31	74.33 ± 0.39	P < 0.05
Protein	23.5 ± 0.56	19.4 ± 0.31	19.89 ± 0.07	P < 0.05
Fat	5.9 ± 0.42	4.6 ± 0.75	10.89 ± 0.07	P < 0.05
Ash	1.4 ± 0.12	1.8 ± 0.14	1.26 ± 0.14	P < 0.05
Carbohydrate	1.73 ± 0.32	1.47 ± 0.01	0.29 ± 0.14	P < 0.05
Fiber	2.78 ± 0.1	2.3 ± 0.12	1.82 ± 0.31	P < 0.05

Values were reported as means ± S.D. of triplicate groups of five fish ( n = 15); significance: P < 0.05.

Fatty acid composition

The fatty acid contents varied widely among the three tested groups of fish, shown in Table 2. The total saturated fatty acids (SFAs) in mackerels was higher than in the other two groups (1.985%). The total SFAs in sardines were 1.292%. In anchovies, the SFAs were 1.597%. Of the three groups of fish studied, the mono-unsaturated fatty acids was 2.949% in mackerels, 1.552% in anchovies, and 0.488% in sardines. In mackerels, the total PUFAs were maximum (44.516%). In anchovies, the total PUFAs were 39.161%. The total PUFAs in sardines were less when compared to the other two groups (37.757%). The omega-3 fatty acids, DHA, and EPA are richly present in all the three groups of fish tested. The availability of EPA in sardines, anchovies, and mackerels was 11.53 ± 0.74%, 12.25 ± 1.61%, and 18.257 ± 2.41%, respectively. The amount of DHA in sardines, anchovies, and mackerels was 21.47 ± 2.36%, 20.28 ± 1.54%, and 19.582 ± 2.54%, respectively.

Table 2:

Fatty acid composition of sardines, anchovies, and mackerels.

Fatty acid	Fatty acid in different fishes (%)
	Sardines	Anchovies	Mackerel	Significance
Saturated fatty acids (SFAs)
Myristic acid	0.239 ± 0.02	0.241 ± 0.27	0.523 ± 0.08	P < 0.05
Palmitic acid	0.401 ± 0.09	0.313 ± 0.42	0.419 ± 0.56	P < 0.05
Stearic acid	0.442 ± 0.15	0.462 ± 0.18	0.663 ± 0.18	P < 0.05
Arachidic acid	0.210 ± 0.03	0.581 ± 0.07	0.580 ± 0.09	P < 0.05
Total SFAs	1.292	1.597	1.985
Mono-unsaturated fatty acids (MUFAs)
Palmitoleic acid	0.141 ± 0.42	0.107 ± 0.54	0.204 ± 0.69	P < 0.05
Oleic acid	0.197 ± 0.09	0.825 ± 0.06	1.225 ± 0.09	P < 0.05
Gadoleic acid	0.150 ± 0.08	0.620 ± 0.12	1.520 ± 0.09	P < 0.05
Total MUFAs	0.488	1.552	2.949
Polyunsaturated fatty acids (PUFAs)
Linoleic acid	0.123 ± 0.17	0.280 ± 0.35	0.330 ± 0.58	P < 0.05
a-Linolenic acid	0.110 ± 0.01	0.341 ± 0.08	0.420 ± 0.01	P < 0.05
e-Linolenic acid	0.124 ± 0.007	1.260 ± 0.82	2.260 ± 0.82	P < 0.05
Eicosadienoic acid	0.39 ± 0.02	0.54 ± 0.34	1.040 ± 0.74	P < 0.05
Eicosatrienoic acid	0.14 ± 0.06	0.80 ± 0.04	0.215 ± 0.05	P < 0.05
Arachidonic acid	3.87 ± 0.14	3.41 ± 0.64	2.412 ± 0.84	P < 0.05
Eicosapentaenoic acid	11.53 ± 0.74	12.25 ± 1.61	18.257 ± 2.41	P < 0.05
Docosahexaenoic acid	21.47 ± 2.36	20.28 ± 1.54	19.582 ± 2.54	P < 0.05
Total PUFAs	37.757	39.161	44.516

Values were reported as the fatty acid percentage distributions (% w/w of total fatty acids). Means ± S.D. of triplicate groups of five fish ( n = 15); significance: P < 0.05.

Ocular disability and diet

The results show that the following vision-related complications: macular edema, optic neuropathy, myopia, double vision, dry eye syndrome, and color blindness were seen less in respondents depending on the fish diet ( Fig. 1). Cooking fish has less impact on the biochemical nature of fatty acids ( Chen et al., 2022). The incorporation of omega-3 PUFAs into food products has a chance for oxidative degradation; therefore, encapsulation is needed to enhance oxidative stability ( Homroy et al., 2024). The various ocular parameters were recorded in the respondents according to the frequency of fish intake in their diet per week. The time interval covers fish intake once a week, twice a week, thrice a week, and occasionally. Macular edema was reported in 30 patients (30 eyes). Among the patients, macular defects were seen in 16.75% of respondents who consumed >500 g of seafood every week, 26.7% among the 300-500 g/week consumers, 20.0% in those who consumed <300 g/week, and 36.7% in occasional seafood users. Optic neuropathy was less in respondents consuming seafood >500 g/week (13.3%), and among the respondents consuming 300-400 g of seafood, optic neuropathy was found in 20.0% of cases. Among the respondents consuming seafood <300 g/week, the incidence of optic neuropathy was elevated (23.3%), but in occasional seafood consumers, optic neuropathy was high (43.3%). Among the respondents with myopia, 56.7% occasionally consumed seafood. In people taking seafood >500 g/week, the incidence of myopia was only 10.0%. A positive correlation was observed between the nondevelopment of myopia and the seafood diet. Among the 30 eyes diagnosed with dry eye syndrome, its incidence was seen only in 16.7% of cases consuming seafood >500 g/week. At the same time, dry eyes were reported in 33.3% of people who occasionally included seafood in their diet.

Figure 1:

Prevalence of ocular problems among the patients identified for vision issues and their dietary intake of seafood. CB, color blindness; DES, dry eye syndrome; DV, double vision; ME, macular edema; MY, myopia; OP, optic neuropathy.

The occurrence of color blindness was not reported in respondents who consumed seafood >300 g/week of seafood. However, in occasional users, the incidence was 76.6%. Another ocular problem, double vision, was seen more often in people with occasional seafood diets (50.0%). However, among people consuming seafood >500, 300-500, and <300 g/week, the incidence of double vision was 14.29%, 20.61%, and 25.80%, respectively. As per the statistics collected from the metadata from people visiting a tertiary care eye hospital, there is a positive correlation between seafood intake and nonoccurrence of eye defects.

The linear relationship between the different ocular problems and seafood intake was correlated using Pearson’s correlation coefficient. Statistical analysis of the correlation between seafood consumption and ocular problems confirmed the interrelationship, shown in Table 3. Pearson’s coefficient of correlation analysis showed that for all the respondents with seafood eating habits, there was a negative correlation between the development of eye problems and the ρ (“rho”) factor was <1 for all eye problems. In the case of macroedema, the Pearson coefficient was 0.265 for seafood consumers and 1 for occasional food consumers. Therefore, there is a good correlation between the incidence of macular edema and a less seafood diet. In respondents with a habit of eating fish, the incidence of “optic neuropathy” is less (a rho factor of 0.530).

Table 3:

Pearson’s correlation coefficient factor between food habits and the development of ocular defects.

S. No	Presence of ocular defects	Respondents	Pearson population correlation coefficient ρ (rho)
1	Macular edema	Respondents without seafood eating habits ( n = 30)	1
		Respondents with seafood eating habits ( n = 30)	0.265
2	Optic neuropathy	Respondents without seafood eating habits) ( n = 30)	1
		Respondents with seafood eating habits	0.530
3	Myopia	Respondents without seafood eating habits	1
		Respondents with seafood eating habits	0.038
4	Dry eye syndrome	Respondents without seafood eating habits	1
		Respondents with seafood eating habits	0.109
5	Color blindness	Respondents without seafood eating habits	1
		Respondents with seafood eating habits	0.352

If the ρ (rho) value is near ± 1, it is a perfect correlation. If the coefficient value lies between ± 0.50 and ±1, then it is said to be a strong correlation. If the value lies between ± 0.30 and ± 0.49, then it is said to be a medium correlation. When the value lies below ± 0.29, there is a slight correlation, and no correlation occurs when the value is 0.

DISCUSSION

Estimating the proximate composition and fatty acid contents in the most common fish consumed by the respondents (sardines, anchovies, and mackerels) showed a rich presence of protein and fatty acids. All fish species have a high protein content, and the protein content varies depending on the species. In this study, the protein content in the chosen three fishes was above 62%. Regular fish intake provides protein and promotes immunity ( Balami et al., 2019). The fatty acid contents in the three groups of food fish showed a rich presence of PUFAs (37.757% in sardines, 39.161% in anchovies, and 44.516% in mackerels). In this study, all three fishes consumed had high amounts of DHA and EPA. Regular fish consumption has been reported to enhance the working mechanism of the macula. The macula is a part of the retina and a key to vision ( Moschos et al., 2018). It has been reported that regular fish consumption reduces the risk of AMD ( Zhu et al., 2016). Omega-3 fatty acids are abundant in sardines, anchovies, mackerel, rainbow trout, and salmon ( Uçak et al., 2019).

The results of clinical analysis of eye problems and the dietary habits of respondents showed that the regular consumption of seafood >500 g/week reduced the risk of developing ocular defects. At the same time, the prevalence of ocular problems was high among the people not consuming seafood. The major reasons are the beneficial omega-3 fatty acids, vitamins, and minerals present in seafood. The impact of seafood in protecting the eyes from diseases is quite evident from the lower incidence of ocular defects in people with respect to the quantity of seafood they consume. Pearson’s correlation between the fish-based diet and nonfish food consumption habits and the prevalence of eye disorders confirms seafood’s importance.

All ocular diseases diagnosed among the respondents were less among the good seafood consumers. It has been reported that regular fish consumption (at least twice per week) reduces retinal problems by widening the mean retinal arteriolar diameter and slightly narrowing the mean retinal venular diameter ( Kaushik et al., 2008). The fish-based diet is rich in long-chain omega-3 PUFAs (EPA, DPA, and DHA). People who regularly consume fish (at least twice per week) have a healthy retinal microvasculature profile and low risk of cardiovascular disease ( Gopinath et al., 2017). AMD is a major factor in vision loss and is common in older people. Adding fatty fish to the diet prevents AMD formation by preventing neovascularization and influencing the retinal pigments ( Fan and Song, 2022). The high amount of omega-3 fatty acids (DHA and EPA) present in the respondent’s seafood diets are reported to be associated with the photoreceptor cells of the retina and highly influence retinal function ( Zanke and Kustra, 2020). This study confirmed that fish consumers are less susceptible to ocular disabilities.

Near-sightedness (myopia) is another problem in vision. Regular intake of seafood in the diet prevented the myopia epidemic ( Wong et al., 2021). An alarming report says that the global myopia problem may increase by 49.8% in the global population by 2050, which may lead to irreversible blindness. During the COVID-19 lockdown period, increased exposure to digital devices aggravated myopia ( Navel et al., 2020). Therefore, as per this study, regular seafood intake can prevent myopia problems from exploding.

Regular seafood intake helps overcome macular degeneration, diabetic-related retinal problems, and glaucoma. According to a WHO report, of the 2.2 billion people suffering from some eye diseases, 196 million are related to AMD, 146 million with diabetic-related retinal defects, and 76 million with glaucoma. Furthermore, nearly 200 million eyes worldwide are affected by cataracts, which cause one-third of worldwide blindness ( World Health Organization, 2019). Reports show that food supplementation can reduce the epidemic of eye disorders ( Rusciano et al., 2020). As reported in this study, regular seafood intake reduces the development of many eye disorders. Regular consumption of oily fish containing DHA and EPA reduces the risk of developing eye disorders by 69% ( Augoode et al., 2008). Recently, seafood products have received much attention by yielding preventive and therapeutic agents to cure eye diseases ( Krueger et al., 2022). People with higher fish intake were less likely to have severe diabetic retina. Higher fish intakes widen the retinal vascular caliber and reduce disease impact ( Chua et al., 2018). Studies indicate that a diet with omega-3 fatty acids such as DHA enhances the development of photoreceptors, and high DHA concentrations in the retina promote the well-functioning of rhodopsin, a pigment in the photoreceptor rod cells ( Christen et al., 2011). Omega-3 supplementation also prevents macular degeneration and dry eye formation ( Zhang et al., 2020). Long-chain PUFA fish oil remediates inflammatory dry eye disease and AMD ( Wang and Daggy, 2017). As fish food, mainly sardines and anchovies, is rich in omega-3 fatty acids, its influence on the respondents’ reduced AMD ocular problems was reported ( Wang and Daggy, 2017). Seafood with a high concentration of n-3 long-chain PUFAs protects against AMD ( Merle et al., 2013). Dietary habits with regular fish intake provide omega-3 fatty acids as good anti-inflammatory antioxidant agents that influence retinal functions ( Krueger et al., 2022). Another study confirmed that people who consume high amounts of fish and shellfish add rich omega-3 fatty acids into their system, making them significantly less susceptible to ocular disabilities ( Swenor and Ehrlich, 2021).

CONCLUSION

The present study shows that the inclusion of sea food provides the essential fatty acids that guard the vision from oxidative stress and impairment. As reported in previous clinical studies, it is confirmed that a regular seafood diet is vital for eye health and plays a defensive role in protecting the vision as a natural food-borne nutrient resource. As the seafood diet contains many omega-3 fatty acids, their inclusion in the diet supplies rich antioxidants and reduces the development of macular edema, optic neuropathy, myopia, dry eye syndrome, color blindness, and double vision. This study recommends sufficient seafood-related diets to prevent the development of many ocular disorders.

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