ASSESSMENT OF PLASMA ZINC STATUS OF SENILE CATARACT AND NON-CATARACT ELDERLY PATIENTS IN MID-WESTERN NIGERIA- A CASE STUDYOF EDO AND DELTA STATES OF NIGERIA.
ABSTRACT
Cataract is the opacification of the crystalline lens, which may result in visual impairment and subsequent blindness. Incidence of cataract is distinctively more in tropical/ developing countries where pronounced exposure to sunlight and profound nutritional deficiencies are prevailing. Zinc is a trace element essential in human nutrition, ubiquitous in cells, significant in membrane function and cellular metabolism like protection of lens from oxidative damage and photochemistry of vision. Deficiency of zinc may be due to decreased intake, metabolic disorders, poor absorption and medication and may result in prolonged dark adaptation time, night blindness, retinal degenerations and cataract. The aim of this study was to assess the level of zinc in cataract and non-cataract elderly patients in Nigeria
. Five hundred senile cataract and five hundred non-cataract respondents (males and females), ³ 60 years, without any other underlying factor that may cause visual impairment, were randomly (simple) selected among patients attending eye clinics of the teaching hospitals in Irrua and Benin City and general hospital Sapele. Blood samples were assessed by computerized atomic absorption spectroscopy and questionnaires were used to estimate dietary pattern (Modified Helen Keller International food frequency method). Using a baseline of plasma zinc levels < 1,050 mg/L, 38% of cataract and 17% of non-cataract respondents had deficient zinc status while the questionnaire showed 48% cataract and 21% non-cataract patients had reduced dietary zinc intake; with all the zinc deficient patients complaining of prolonged dark adaptation and night blindness. Physiological, biochemical and dietary parameters influence zinc status in the elderly which severally affect vitamin A metabolism with regard to absorption, and transportation. Majority of respondents with deficient zinc status suffered night blindness, which may occur in zinc deficiency even with normal vitamin A status. Zinc deficiency may, therefore, be implicated in the high prevalence of cataract manifestation in developing countries. Additionally, zinc deficiency may contribute to the high incidence of night blindness usually involved in vitamin A deficiency (VAD) in areas with high prevalence of VAD.
KEYWORDS: Cataract, Zinc, Nutritional Status, Eye
FRENCH
ETUDE DU PLASMA DE ZINC DANS LA SITUATION DE CATARACTE ET NON-CATARACTE SENILE CHEZ LES MALADES ASSEZ AGES DANS LE MIDWEST DU NIGERIA UNE ETUDE DE CAS DES ETATS DE EDO ET DU DELTA DU NIGERIA.
NOTE DE SYNTHESE
La cataracte représente une opacification du cristallin qui peut donner lieu à un affaiblissement visuel et plus tard à la cécité. L'incidence de la cataracte est typiquement plus fréquente dans les pays tropicaux/en voie de développement où prévaut une exposition marquée à la lumière solaire ainsi que des déficiences nutritionnelles profondes. Le zinc est un oligo-élément essentiel dans l'alimentation humaine, omniprésent dans les cellules, important dans la fonction des membranes et du métabolisme cellulaire tels que la protection des lentilles cristallines contre les dégâts d'oxydation et la photochimie de la vision. La déficience en zinc peut être due à une faible ingestion, des troubles métaboliques, une mauvaise absorption et une médication. Elle peut se traduire par l'adaptation prolongée à l'obscurité, la cécité de nuit, la dégénération de la rétine ainsi que la cataracte. La présente étude a pour objet d'évaluer le niveau de zinc chez les malades assez âgés de cataracte et de non-cataracte du Nigeria qui ne présentent aucun autre facteur fondamental qui peut causer un affaiblissement visuel. Un échantillon aléatoire (simple) de cinq cents cas de cataracte sénile et de cinq cents cas de non-cataracte (hommes et femmes), âgés de plus de ³ 60 ans. Ces personnes ont été sélectionnées parmi les malades en consultations ophtalmologiques des hôpitaux universitaires de Irrua et Benin City et de l'hôpital général de Sapele. Des échantillons de sang ont été analysés par la spectroscopie informatisée d'absorption atomique. En outre, des questionnaires ont été utilisés pour étudier le modèle diététique (Méthode modifiée de la fréquence alimentaire de Helen Keller International). En utilisant des points de comparaison dont les niveaux de plasma de zinc sont < 1,050 mg/L, 38% des personnes interrogées à cataracte et 17% de celles qui n'ont pas de cataracte ont une déficience en zinc. D'autre part, le questionnaire a révélé que 48% de cas de cataracte et 21% de cas non-cataracte avaient diminué la quantité de zinc absorbée dans la nourriture. La plupart des malades ayant une déficience en zinc se plaignent d'une adaptation prolongée à l'obscurité et d'une cécité de nuit. Les paramètres physiologiques, biochimiques et diététiques chez les personnes assez âgées influencent la condition par rapport au zinc qui affecte sévèrement le métabolisme de la vitamine A, à savoir l'absorption et le transport. La plupart des personnes interrogées qui ont une déficience en zinc souffrent de cécité nocturne, qui peut apparaître à cause de la déficience en zinc même lorsque le niveau de vitamine A est normal. Le manque de zinc peut par conséquent compromettre le niveau élevé des cas de cataracte dans les pays en voie de développement. En outre, la déficience en zinc peut contribuer à une incidence élevée de cécité nocturne, souvent impliquée dans la déficience de la vitamine A (DVA) dans les régions à haute prévalence de DVA.
Mots-clés :: Cataracte, Zinc, Condition nutritionnelle, il)
INTRODUCTION:
The world's elderly population is growing at a rate of 2.4% per year [1]. This implies that by the year 2020, the year envisaged by the World Health Organisation (WHO) for there to be sight for all, a good number of Africans and more in developed countries would be 65 years and above. This would be because of improved sanitation, easier access to drugs, improved education, awareness and efficient and effective social engineering. Additionally, the leading causes of death among the elderly, due to advances in biomedical research, would probably be more properly handled. However, optimal ocular health shall be a major quality of life issue for the elderly by 2020 because sustained good vision enhances optimal health, improves mobility and encourages self-reliance. Currently, epidemiological, clinical and biochemical evidence are mounting on the beneficial roles of nutrition in the sustenance of good eye health. Of particular interest in this study, is the relationship between zinc metabolism and cataractogenesis among the elderly. Cataract is the opacification of the crystalline lens of the eye, which may result in visual impairment and subsequently blindness [2]. It is the major cause of blindness worldwide and Africa has the lion's share [3]. Between 45 65% of blindness worldwide is attributable to cataract [4]. Cataract has the propensity of onset in more than 60% of people above 65 years but in developing countries, there is rather disturbingly, an increase in occurrence in people less than 50 years [5]. Incidence of cataract is distinctively more in developing countries where pronounced exposure to environmental hazards, poverty and profound nutritional deficiencies are prevailing.
Similar to other vital organs of the body, the eye must be healthy in a healthy body for which good nutrition is essential and sustainable. Scientists concur that the human body requires about 50 essential nutrients. Some are beneficial to the eye directly, others indirectly while some still fall in both categories, implying that they are beneficial to the body in which the eye is dependent [6].
Zinc is an essential mineral in human nutrition and because of its unique chemistry, serves essential structural, catalytic and regulatory functions in biological systems. Zinc is ubiquitous in all cells [7]. Since the documentation of the essentiality of zinc in human nutrition, considerable scientific findings have revealed the multiple and complex ocular and systemic functions of zinc. Currently, zinc is a major constituent of more than 200 matallo-enzymes involved in protein, lipid and carbohydrate metabolism and nucleic acid synthesis and degradation [8]. The diversity of zinc in optimal health includes growth and development, reproduction, immune and sensory functions, antioxidant protection and the stabilization of membranes [9]. The highest concentrations of zinc in the body are in the eye, prostrate and bone [10]. For the eye, zinc protects all the tissues in the eye against oxidative damage and ocular birth defects. Zinc is extremely vital in the photochemistry of vision, stabilization of intraocular pressure (IOP) and protection from early onset of cataract, optic neuritis and retinal degenerations [7].
Nutritional deficiency of zinc may be due to decreased intake, metabolic disorders, poor absorption and medication. This may result in ocular birth defects, prolonged dark adaptation time, night blindness, retinal degenerations and cataract occurrence. Systemic manifestations include retarded growth, depressed immune function, anorexia, dermatitis, altered reproductive performance, skeletal abnormalities, diarrhea and alopecia. Children, pregnant women and the elderly are more susceptible to zinc deficiency [11]. In the elderly, presence of disease states (such as diabetes), use of certain medications and supplements may precipitate secondary zinc deficiency states [12].
The objectives of this study therefore, were to assess the plasma zinc status of senile cataract and non cataract elderly patients attending eye clinics in Midwestern (Edo and Delta States) Nigeria and the investigation of possible relationship between utilization, under-utilization and mal-utilization of zinc and the manifestation of cataract.
MATERIALS AND METHODS
This study was performed according to stipulated regulations of the Helsinki declaration, University of Benin and Otibhor Okhae Irrua Teaching Hospitals guidelines.
Subjects: A total of 1000 elderly male and female patients were sampled. All the subjects were 60 years and above, attending eye clinics in the following hospital locations.
Locations: (1) University of Benin Teaching Hospital, Benin City, Edo State
(2) Otibhor Okhae Teaching Hospital, Irrua, Edo State
(3) Central Hospital, Benin City, Edo State
(4) St. Thomas Hospital, Sapele, Delta State
Both Edo and Delta States were created out of the old Midwestern region of Nigeria.
Selection criteria: The sample population selected were elderly patients diagnosed with cataract (500) and those not diagnosed as suffering cataract (500). Also, all the patients had no other underlying factor that could contribute or manifest into cataract. Clinical assessment and case history were the parameters used for selection criteria.
Sampling technique: The simple random sampling technique was applied.
Consent to participate: A written consent was received, duly signed, by each of the respondents.
Questionnaires: Structured questionnaires were used to assess the dietary and other nutritional parameters of the respondents. The questionnaires also provided information about the assessment of ocular, clinical and physical examinations.
METHODS
A. Dietary patterns: Questionnaires were used to assess the dietary pattern of the sample population using the Food Frequency Method by applying a reference time period of one week to assess intakes of a variety of nutrients rich in zinc, which were subsequently ranked into high and low only [13].
B. Clinical signs and symptoms: The Keller Medic Lux Ophthalmoscope was used to differentially diagnose cataract and non-cataract patients. Also it was used to ascertain the absence of other retinal disorders that could show similar signs and symptoms of zinc deficiency like retinitis pigmentosa, achromatopsia, optic atrophy among others. Data on dark adaptation time (vision restoration time) was collected using a New SF Stardust rechargeable Lantern. The light from the lantern was flashed into each patient's eyes for 60 seconds and then the light in the dark room (eye examination room) was switched off. The time it took to recognise the largest letter in the visual acuity chart (LogMAR visual acuity chart) was the dark adaptation time or vision restoration time for this study.
Qualitative data on night blindness was obtained through interviews, which were conducted by trained interviewers.
C. Blood sample collection: Qualified health personnel working in the health institutions used for this study assisted in the blood sample collection. Blood samples were collected according to international standards as recommended by Cheesbrough (2000)[14] and this was centrifuged into plasma. Anticoagulated venous blood was collected according to the technique of Cheesbrough (2000), deproteinized with 6% trichloroacetic acid after which it was diluted into a ratio of 4:9 with deionized water and stored without freezing. All the tubes used were evacuated to ensure they were trace element free. Also, all blood assays were performed in contamination controlled laboratory environment. A Pye Unicam 969 atomic absorption spectrometer fitted with a zinc hollow cathode lamp was used to assay for zinc.
D. Statistical analysis of data: Statistical analysis of data was by comparison of normal and abnormal zinc status in the perspective of dietary intake, clinical signs and symptoms and biochemical parameters (P< 0.05) using the statistical d-test to compare percentages of the samples.
RESULTS
For this study, we applied a multi-marker model of nutritional assessment systems. Biochemical, dietary and clinical parameters were succinctly interpreted. Dietary assessment as seen in Table 1 shows that 48% and 30% cataract and non-cataract patients, respectively, had zinc deficiency. The increase of zinc deficiency among the study population was rather on the high side. However, the modification of the Helen Keller International Food Frequency method improved further, the validity of the result [13, 15]. A reference period of one week was used to reduce the incidence of recall bias, which is normally high among the elderly.
The results obtained on night blindness and dark adaptation time (vision restoration time) also had a high prevalence. This could be due to the high rate of zinc deficiency, aging and dietary factors. Also, a high incidence of night blindness was recorded among children from same location [16].
Because male and female results were combined, an average of the zinc requirements for adult males and females was obtained which is 1,050 mg/L. (Figure 1)
Figure 1: Plasma Zinc Levels for Cataract and Non Cataract Elderly Patients
DISCUSSION
Zinc concentration in foods varies widely but it is abundant in meats, especially red meat and sea foods. It is also abundant in whole cereals (the embryo portion) and eggs among other foods. Generally, animal products are better dietary sources than plant products [17]. This is due to phytates and fibres in plant products which bind with zinc in the gastrointestinal tract to form insoluble zinc chelate complexes whose effect may be enhanced by high dietary calcium.
The metabolism of zinc is regulated by variation in absorption and excretion, which is a response to changes in dietary intake. Dietary zinc requirements can be defined as the minimum zinc intake that will support optimal growth and metabolism [17]. Biochemical, physiological and nutritional factors affect zinc absorption and utilization. Though pregnant women and children are at risk of hypozincaemia, the elderly are at higher risk due to the higher zinc requirements for their homeostasis [18]. The decreased intake, poor absorption and excess excretion that manifest in the elderly may be implicated with socioeconomic status, certain systemic disorders (diabetes, chronic liver/ kidney diseases) and excessive use of certain trace minerals (calcium, copper and iron). Some medications common to the elderly (Diuretics, corticosteroids, penicillamine) may also contribute to zinc deficiency. These have been implicated with the high incidence of marginal zinc deficiency in the United States [10]. This also substantiates the high incidence recorded in our study in an environment with a high incidence of poverty (Figure 1).
The biochemical mechanisms of zinc metabolism are quite remarkable and it is ubiquitous in all cells. However, some of these biochemical/physiological mechanisms could be elucidated on the perspective of deficiency states. Majority of zinc-induced clinical manifestations may be accounted for by hinging on membrane damages whose remediation could be by enhancement of the functions of ATPases, thiol groups with zinc, whose inactivity encourages lipid peroxidation [19]. This is because many findings have espoused pronounced lipid peroxidation during zinc deficiency [20]. As earlier stated, this is of great significance because studies have implicated oxidative damage to the manifestation of degenerative diseases like cataract, cancer and macular degenerations [2]. Earlier studies have shown that zinc is vital in the maintenance of lens health. These studies reported low levels of zinc in people developing cataract [21]. Additionally, levels of some antioxidant vitamins tend to be low in senile cataract patients [22]. In 1995, 50 million people were blind worldwide [3]. The same 1995 projection shows that by 2002, more than 55 million people shall be blind. More than 55% of the blindness is due to cataract. The majority of them are from Africa, which has a blindness prevalence rate of more than 1%, the highest in the world.
Unfortunately, Africa has between 500,000 and 1,000,000 people to one Ophthalmologist, which implies that more people in Africa will be blind in the years ahead. Again, more than 90% of the entire eye care professionals work in urban areas. In Kenya for example, with a population of about 30 million people, there is a blindness prevalence of 0.7% with cataract contributing 43% and in 1999 alone, about 37,000 cases of cataracts were identified and only about 12,000 were operated on surgically [23]. Nigeria has about 1 million blind people and majority of them (>55%) the blindness is due to cataract [24].
Recent reports (2002) indicate more than 70% of the Nigerian population live on less than one dollar a day, and malnutrition is prevalent and the number of people who are undernourished are on the increase because, just as poor countries tend to have high rates of malnutrition, the poorest segment of the population within a country is the most malnourished [25].
In the same report, Nigeria is ranked 186th among 207 countries based on Gross National Income (GNI). This is a case for sober reflection, because the nutritional status of Nigerians has been shown to be relatively poor [26] and due to prevailing socioeconomic, political and environmental factors have been sliding further down. With little awareness on nutritional requirements due to educational, socioeconomic, cultural limitations, it is therefore not surprising that there is increased nutritional (zinc) deficiencies. The major staple foods of these elderly people include cassava and yam. These have zinc content. Additionally, the local grains have high phytate content. The commonly consumed cassava products may also have high cyanide content [27].
Moreover, the seasonality of farming in Nigeria may affect zinc status of the elderly [28] implying that the incidence of cataract would be on the increase.
Diagnosed cataract may mature to the stage of gross visual reduction before surgery. Surgery for cataract in Nigeria is unaffordable and due to socio-cultural factors, the elderly are less enthusiastic in going for surgery. The most common corrective procedure for cataract in the world is cataract surgery. In the U.S.A., cataract surgery accounts for the highest health care bill [29]. Scientific data show that delaying progression of cataract by just 10 years could reduce the number of surgeries by 45% [30]. This can be done by improving the nutritional status of the elderly by dietary and / or supplementary strategies. Zinc is one of the vital components of those necessary micronutrients.
CONCLUSION
Trends in nutritional research are indicating that optimal health may be attained with optimal nutrition. Research findings further substantiate the fact that nutritional supplements and good dietary consumption play significant roles in the remedy and prevention of degenerative diseases. Good vision at old age greatly improves the lifestyle of the elderly. Our findings in this study show a relationship between zinc deficiency and increased occurrence of cataract among the elderly. This deficiency may be due to under-utilization and mal-utilization of Zinc in the diet and lack of supplementation for zinc. These could be tied to ignorance and poverty. Also, micronutrients are vital for the delay or amelioration of age related diseases. Zinc is a vital part of those nutrients that would guarantee optimal health. Further studies need to be done on the potential of zinc in the prevention of cataract occurrence.
Table 1
Dietary, Clinical and Biochemical Results
| Measurement Parameter |
Cataract |
Non-cataract |
| |
Frequency |
Percentage |
Frequency |
Percentage |
| DIETARY |
|
|
|
|
| Normal dietary intake (Normal zinc status) |
260 |
52 |
395 |
79 |
| Deficient dietary intake (Zinc deficiency Status) |
240 |
48 |
105 |
21 |
| CLINICAL SIGNS / SYMPTOMS |
|
| Normal night vision |
245 |
49 |
355 |
71 |
| Night blindness (Abnormal night vision) |
255 |
51 |
380 |
29 |
| Normal dark adaptation time |
265 |
53 |
380 |
76 |
| Abnormal dark adaptation time |
235 |
47 |
120 |
24 |
| PLASMA ZINC LEVELS |
|
| Zinc levels < 1,050mg/L |
190 |
38 |
85 |
17 |
| Zinc levels > 1,050mg/L |
310 |
62 |
415 |
83 |
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