«Wild Edible Plant Consumption and Age-Related Cataracts in a Rural Lebanese Elderly Population: A Case control Study By Joelle Zeitouny School of ...»
There are around 6.3 million blind and around 22 million people with visual impairment in the Middle Eastern Region according to the WHO (2005). In Lebanon, 0.6 % of the population is blind and 3.9% suffers from low vision (Mansour et al., 1997). Cataracts are responsible for 41.3% of the causes of blindness and macular degeneration for 3.8% (Mansour et al., 1997). Lutein and zeaxanthin have been shown to have a protective role against both age-related cataract and age-related 28 macular degeneration; however, since the prevalence of macular degeneration in Lebanon is very low, the present study will only investigate the effect of the intake of lutein and zeaxanthin on the incidence of age-related cataracts. Many factors contribute to the low prevalence of macular degeneration: a shorter lifespan of individuals living in eastern Mediterranean countries than that of those living in the United States or Europe, an early onset of cataract which may prevent light-related damage to the macula, and the fact that the retinal pigment epithelium of dark skinned individuals may protect against macular damage (Tabbara, 2001). Several epidemiologic studies have also shown that dark-colored irises decrease the risk for developing age-related macular degeneration (Hammond et al., 1996; Nicolas et al., 2003), even though some studies found no significant association between iris color and the incidence of age-related macular degeneration (Khan et al., 2006).
Moreover, most of the evidence on the relationship between lutein and zeaxanthin and the eye diseases of aging (i.e. age-related cataract and age-related macular degeneration) is based on epidemiological studies done in the United States.
The particularity of the present study is that it will try to establish a link between dietary diversity in general, and green vegetable consumption in particular, and an eye disease of aging (age-related cataract) in a developing country where the diet is characterized by a heavy reliance on refined grains as the primary source of energy (WHO, 1998), and where cataracts account for more than 40% of the causes of blindness (Mansour et al., 1997). Furthermore, it hopes to promote dietary diversification in Lebanon and the consumption of dark leafy vegetables (esp. wild leafy edible plants) to combat age-related cataracts and improve overall health.
2.7 STUDY OBJECTIVES
1. Assess the relationship between lutein and zeaxanthin intake and age-related
a. Determine if high or low intake of lutein and zeaxanthin is associated with the development of age-related cataracts.
2. Determine the factors that come into play in wild edible leafy greens’ consumption:
a. Develop an in-depth understanding of the role of indigenous knowledge about wild leafy greens’ identification and collection in increasing wild leafy greens’ consumption and improving ocular health.
b. Determine the socio-economic factors that affect the consumption of wild edible leafy greens.
3. Determine whether dietary diversity is linked with the development of age-related cataracts.
3.1 STUDY AREA AND POPULATION The study was part of a project conducted by the American University of Beirut in collaboration with McGill University and funded by IDRC. The project, which started in December 2004, principally aimed to improve dietary diversity in poor communities in Lebanon by promoting the consumption of wild edible plants.
Dr. Malek Batal, the project’s principal investigator, suggested that the study takes place in one of the project’s study sites, Hermel. Hermel is a poor, ethnically homogeneous and fairly traditional rural area of around 100,000 inhabitants situated in the northeast of Lebanon in the Bekaa Valley, 134 km from the capital city of Beirut (Figure 3.1). Due to its location in between the two Lebanese mountain chains, the area receives little precipitation and is semi-arid (US Library of Congress).
Figure 3.1: Map of Lebanon (Lonely Planet).
Approval for the study was granted from the “Research Ethics Committee” of McGill’s faculty of Agricultural and Environmental Sciences and from the “Institutional Review Board” of the American University of Beirut’s Faculty of Medicine. The study was explained in detail to all potential participants and their voluntary consent was solicited. We insured that all subjects thoroughly understood the informed consent (which was translated to Arabic) before signing it. Participants who could not read or write gave their consent verbally and a member of their family was asked to sign for them. Upon completion of data collection, preliminary study results were to be presented to the community at a town meeting but the unfortunate circumstances that took place in summer 2006 in Lebanon prevented that from happening. Nevertheless, such a meeting is to be organized in the near future.
3.2 STUDY DESIGN
A case-control study design was employed to explore the relation between the intake of carotenoids (and especially lutein and zeaxanthin) along with diet diversity and age-related cataract risk. A nutritionist and 3 local community members with previous training in administering questionnaires conducted the interviews in groups of two. A meeting was held with the interviewers before the start of the interviews and a training module was followed to ensure a common understanding of the goals and objectives of the project and the meaning of the questions in the questionnaire.
323.3 SAMPLING PROCEDURE
Our sample size consisted of 100 cases and 100 controls. To reduce sampling bias, cases and controls were both to be selected from a local eye clinic. However, since not enough patients were visiting the clinic and were going instead to nearby Syrian clinics which were much cheaper, 98% of the participants were eventually selected by random walk. The Hermel district comprises the town of Hermel (capital of the district) and a collection of small surrounding villages. Sampling started in the town of Hermel where the survey team spun a bottle or a pen at every crossing to determine the direction to continue and visited the households in the chosen direction in search of patients with age-related cataracts or who have had age-related cataract extraction (who if found and selected were matched with people living in the neighborhood of the same age and gender who have been tested negative for any eye disease during the last eye check-up they had). Each group of interviewers was to recruit 10 participants per day. If not enough participants could be recruited in a certain neighborhood, another direction was randomly chosen until the required number of participants was obtained.
A nutritionist and 3 local community members collected all dietary, demographic, and anthropometric data. All spoke Arabic fluently and understood the dialect particular to the area. Almost all interviews were conducted in the homes of the participants (apart from those conducted in the eye clinic). Data was collected during the month of June 2006 when the wild edible leafy greens’ season was coming to its end. The questionnaires were translated to Arabic and each interview took around 30 to 45 minutes. Two questionnaires were administered to each of the participants. The first collected socio-demographic data and included a 7-day semiquantitative food frequency questionnaire. The second consisted of a 3-month food frequency questionnaire that was administered a week after data collection for the
3.4.1 Socio-demographic assessment Socio-demographic data was gathered from the participants during the first interview. As a matter of fact, the first questionnaire collected demographic information, data on socioeconomic conditions, and data on indigenous knowledge about wild plant identification and collection.
3.4.2 Dietary assessment
Two structured semi-quantitative food frequency questionnaires (a 7-day and a 3-months food frequency questionnaire respectively) separated by a one-week interval were used to describe patterns of food intake. Calibrated local utensils were available at each interview to help participants describe quantities of food eaten. The food-frequency questionnaires included a total of 82 food items each but were not exhaustive: they were composed of local foods rich in lutein and zeaxanthin, local foods rich in other carotenoids (such as β-carotene and lycopene), and staple foods.
Food items were divided into 9 categories: breads and cereals, fruits, vegetables, beans, milk and dairy products, meats and eggs, fats and oils, drinks, and wild edible leafy greens. The participants were asked to recall their usual frequency of consumption of a given food item and the amount consumed daily, weekly, or monthly.
The CANDAT Nutrient Calculation System (2005) was used to process the dietary data obtained from the food frequency questionnaires. A user file was created to include Lebanese foods (such as labneh, kishek, etc.) and local wild edible leafy
3.4.3 Diversity indexes For this study, two indexes of diversity were used: Food Variety Score (FVS) and Dietary Diversity Score (DDS) (Ogle et al., 2001). FVS was obtained from a count of the number of foods consumed during the last 3 months and was calculated for the total number of foods consumed, foods rich in lutein and zeaxanthin, foods rich in retinol activity equivalents (RAE), foods rich in β-carotene, foods rich in αtocopherol, and foods rich in vitamin C. Food items that were considered to be rich in lutein and zeaxanthin were those that contained 500 μg or more of lutein and zeaxnthin per portion size: this amount constituted 25% of the mean daily intake of lutein and zeaxanthin for our study population and approximately 50% of the mean daily intake of lutein and zeaxanthin according to the literature. Thirty-two food items out of 82 were thus considered to be rich in lutein and zeaxanthin. Using a similar logic, the 32 food items highest per portion size in any other nutrient studied (retinol activity equivalents (RAE), β-carotene, α-tocopherol, and vitamin C) were considered to be rich in that particular nutrient. However, only 29 food items out of the possible 82 contained non-negligible amounts of α-tocopherol per portion size; they were the ones considered to be “rich” in α-tocopherol.
DDS was obtained from a count of food groups consumed over the last 3 months. Two DDS were created. Both had a total number of 8 food groups and included starches, fruits, vegetables, legumes, dairy products, meats, fats and oils.
The first DDS however also comprised leafy greens while the second comprised wild leafy greens.
Age was obtained from the national identity card of each participant. Height and mid-upper arm circumference were measured using a measuring tape and were recorded to the nearest one-tenth centimeter. When standing height could not be measured (because of postural problems or confinement to bed), knee-height was used to estimate it with equations derived from North American people and based on age and gender (Chumlea et al., 1994). Weight was measured with a digital scale and was recorded to the one-tenth kilogram. Body Mass Index (BMI) was computed by weight (kg)/ height (m2).
3.5 DATA ANALYSES
Data were analyzed using the Statistical Package for Social Sciences (SPSS) for Windows version 13.0 (SPSS Inc., 1989-2004). Nutrient intakes were not normally distributed, therefore the Mann-Whitney U test, the nonparametric equivalent of Student's t-test, was performed to test the differences between cases and controls. Spearman’s rho correlation coefficient was used to assess the degree of association between the intake of lutein and zeaxanthin and that of wild leafy greens.
In addition, a stepwise multiple linear regression was used to determine the best predictors of the consumption of wild edible leafy greens. The data on the intake (in grams) of wild leafy greens was not normally distributed and had therefore to be logtransformed before the regression could be run. The independent variables entered into the regression were age, gender, duration of residence in Hermel, marital status, education level, occupation, socio-economic status, smoking, and source of knowledge on wild leafy greens. In the present study, p0.05 was used to indicate statistical significance.
4.1 SAMPLE CHARACTERISTICS Participants were between the ages of 45 and 90 years (Table 4.1). Both male and female participants were approximately the same age (around 67 years old on average). Most participants were illiterate, had always lived in Hermel, and classified themselves as “poor”. In fact, more than three quarters were unemployed, homemakers, or retired. Two thirds of the participants were married. Around three quarters, of both cases and controls, had dark-colored irises. More than half were cigarette or hookah smokers at one point in their lives. However, more cases than controls worked in agriculture, had a family history of age-related cataracts, and a high level of psychological stress.
Mean BMI was 31 and wasn’t significantly correlated with age. BMI ranged from 18 to 47.6 kg/m2 with 1% having a BMI below 18.5 kg/m2, the cut-off point used by the WHO to identify chronic energy deficiency, and 81% having a BMI over 25 kg/m2. MUAC and BMI were statistically significantly positively correlated (ρ= 0.479, p0.01); however, only about 10% of the participants were above the 85th MUAC percentile and surprisingly, as many as 10% were below the 10th MUAC percentile, using the age and gender-specific MUAC percentiles for older men and women examined in the NHANES III (Kuczmarski et al., 2000). Both cases and controls had approximately the same BMI and MUAC on average.
4.2 NUTRIENT INTAKES AND AGE-RELATED CATARACTS
The distribution of the average intakes per day over a period of three months for lutein and zeaxanthin, β-carotene, Retinol Activity Equivalents (or vitamin A), vitamin C and α-tocopherol is described in quantiles along with the mean (Table 4.2).
Values are compared to FAO/WHO recommendations. Participants at the 25th