«Wild Edible Plant Consumption and Age-Related Cataracts in a Rural Lebanese Elderly Population: A Case control Study By Joelle Zeitouny School of ...»
This work is used with the permission of Joelle G. Zeitouny.
© 2007, Joelle G. Zeitouny.
Wild Edible Plant Consumption and Age-Related Cataracts in a
Rural Lebanese Elderly Population:
A Case control Study
School of Dietetics and Human Nutrition
Montreal, Quebec, Canada
A thesis submitted to the Faculty of Graduate Studies and Research in partial
fulfillment of the requirements for a Master of Science
August 2007 © Joelle G. Zeitouny, 2007 i Abstract The Mediterranean diet is characterized by considerable diversity and high consumption of wild leafy greens which are excellent sources of antioxidants, including lutein and zeaxanthin. The latter are the only carotenoids present in the human lens and observational and intervention studies suggest they may be protective against age-related cataracts. To better understand the role of dietary diversity in general (and lutein and zeaxanthin in particular) in preventing age-related cataracts and the determinants of wild leafy greens’ consumption, dietary and socioeconomic data were collected from one hundred cases and controls randomly selected from Hermel, a poor and fairly traditional Lebanese rural area. Results showed that dietary diversity and antioxidants (including but not limited to lutein and zeaxanthin) are inversely related to age-related cataracts and that wild leafy greens seem to substantially contribute to protection against age-related cataracts by optimizing nutrient and antioxidant intake especially in those of low socio-economic status.
ii Résumé Le régime Méditerranéen est caractérisé par une diversité considérable et une consommation élevée de plantes vertes sauvages, qui constituent d’excellentes sources d’antioxydants, y compris la lutéine et zéaxanthine. Ces-derniers sont les seuls caroténoïdes présents dans la lentille humaine et des études observationnelles et interventionnelles suggèrent qu’ils pourraient protéger contre la cataracte liée à l'âge.
Pour mieux comprendre le rôle de la diversité alimentaire en général (et de la lutéine et zéaxanthine en particulier) dans la prévention de la cataracte liée à l'âge et les déterminants de la consommation de plantes vertes sauvages, des données socioéconomiques et alimentaires ont été collectées de cent cas et témoins sélectionnés arbitrairement de Hermel, une région rurale pauvre et traditionnelle Libanaise. Les résultats ont montré que la diversité alimentaire et les antioxydants (y compris mais non limité à la lutéine et zéaxanthine) sont inversement reliés à la cataracte liée à l’âge et que les plantes vertes sauvages sembleraient contribuer substantiellement à la protection contre la cataracte liée à l'âge en optimisant l’apport de nutriments et d’antioxydants, particulièrement chez ceux d’un statut socio-économique peu élevé.
I would like to thank my supervisor Dr. Timothy Johns for the patient guidance, encouragement and advice he has provided throughout my time as his student. I could have not imagined having a better advisor and mentor for my Masters and without his relentless support, and stimulating suggestions, I would have never completed this project. Dr. Johns, thanks for giving me the confidence that I needed and for taking care of me only like my parents would.
I extend my gratitude to my co-supervisor, Dr. Malek Batal for making this project possible and financially supporting it through funds from the International Development Research Center (IDRC), for introducing me to the community of Hermel and for providing invaluable expertise.
Many thanks also to Dr. Harriet Kuhnlein, my only committee member, for her overall contribution and more particularly her thoughtful guidance, at all stages of this study.
A big thank you to all study participants for their generosity and patience, the interviewers (Rajaa, Rana, and Falah) for their understanding and support and Khadije and Neyif for their warm welcome and hospitality.
Completing this work would have been all the more difficult were it not for the support and friendship provided by the other members of the School of Dietetics and Human Nutrition. I am indebted to Louise Johnson-Down and Dina Spigelski for their guidance with CANDAT, Patrick Owen and Yuan Zhou for their priceless help with SPSS and Bronwen Powell for making me feel I wasn’t quite useless as I
Francine for always coming to my rescue.
Thanks also to Dr. Pierre Dutilleul for overseeing the statistical analysis and giving me helpful pointers.
My last thank you goes to my family for fielding transatlantic crisis calls at all hours of the day (and night), for uninterruptedly supporting my decision to do a Masters both morally and financially, and for endowing me with faith to keep me strong and courage to stand up for what I believe in day after day. Mom, Dad, Tino, Chris and Joe, I love you.
This thesis is dedicated to the memories of all the innocent victims of the 2006 Lebanese war, some of whom participated in this project. May they all rest in peace.
Table of Contents
List of Tables
List of Figures
2.0 LITERATURE REVIEW
2.1 THE MEDITERRANEAN DIET AND FOOD DIVERSITY
2.2 WILD LEAFY GREENS AS FOOD
2.3 CAROTENOIDS AND HEALTH
2.4 LUTEIN AND ZEAXANTHIN
2.4.1 About lutein and zeaxanthin
2.4.2 Absorption, transport, and bioavailability
2.4.3 Mechanism of action
2.4.4 Body of evidence to support a protective role for lutein and zeaxanthin in two common eye diseases of aging, cataract and macular degeneration
2.5 OTHER ANTIOXIDANTS AND AGE-RELATED CATARACTS & MACULARDEGENERATION
2.5.1 Other antioxidants and age-related cataracts
2.5.2 Other antioxidants and age-related macular degeneration
2.6 STUDY RATIONALE
2.7 STUDY OBJECTIVES
3.0 SUBJECTS AND METHODS
3.1 STUDY AREA AND POPULATION
3.2 STUDY DESIGN
3.3 SAMPLING PROCEDURE
3.4.1 Socio-demographic assessment
3.4.2 Dietary assessment
3.4.3 Diversity indexes
3.5 DATA ANALYSES
4.1 SAMPLE CHARACTERISTICS
4.2 NUTRIENT INTAKES AND AGE-RELATED CATARACTS
4.3 WILD LEAFY GREENS’ CONSUMPTION
4.4 DIVERSITY SCORES
Table 4.1: Sample characteristics
Table 4.2: Distribution of nutrient intakes compared to the FAO/WHO vitamin recommended nutrient intakes.
Table 4.3: Distribution of energy intakes for males (N=58) and females (N=142) according to their weight and compared to the FAO/WHO/UNU recommended energy intakes for older adults and elderly.
Table 4.4: Comparison of the average 3-month intake of energy (kcal), lutein and zeaxanthin (μg), vitamin A (μg), β –carotene (μg), vitamin C (mg) and α -tocopherol (mg) between cases and controls
Table 4.5: Main sources of lutein and zeaxanthin in the diet of subjects (N=67) with a high intake of lutein and zeaxanthin.
Table 4.6: Comparison of the main sources of lutein and zeaxanthin in the diet of cases (N=26) and controls (N=41) with a high intake of lutein and zeaxanthin.
....... 44 Table 4.7: Collection and consumption of wild leafy greens
Table 4.8: Predictors of the consumption of wild leafy greens
Table 4.9: Comparison of the Food Variety Scores (FVS) and the number of food items rich in lutein and zeaxanthin, vitamin A, β-carotene, vitamin C and αtocopherol consumed over a 3-month period between cases and controls.
................ 48 Table 4.10: Comparison of the Dietary Diversity Scores (DDS) between cases and controls
Figure 2.1: The structures of the predominant carotenoids found in human plasma.
.. 6 Figure 2.2: How the structure of the carotenoids affects their incorporation into biological membranes..
Figure 2.3: The human eye shown in a 3D structure.
Figure 2.4: The structures of the three major components of the macular pigment.
... 9 Figure 2.5: Steps of carotenoid absorption and dietary factors that affect carotenoid absorption
Figure 2.6: Macular pigment optical density versus dietary (μg/d) and serum (μmol/L) lutein and zeaxanthin.
Figure 2.7: Absorption spectrum for lutein
Figure 2.8: Macular pigment optical density and light transmission
Figure 2.9: Funduscopic matter of the human eye and retina
Figure 3.1: Map of Lebanon
Populations living in Mediterranean countries benefit from a longer life expectancy and a lower incidence rate of chronic diseases than Northern Europeans or North Americans (Simopoulos, 2001; Schröder, 2007). Migrant studies say the Mediterranean diet and lifestyle are behind these societal differences, rather than any genetic or racial factors (James et al., 1989; Darmon & Khlat, 2001; Trichopoulou, 2004). As a matter of fact, traditional Mediterranean diets are unquestionably healthier than North European and American diets: they include a significantly large amount and variety of plant foods (such as fruits, vegetables, wild leafy greens, breads, seeds, nuts and olive oil) and thus guarantee an adequate intake of carotenoids, vitamin C, tocopherols, α-linolenic acid, various important minerals, and several possibly beneficial non-nutrient substances such as polyphenols and anthocyanines (Visioli and Galli, 2001).
Lutein and its stereoisomer zeaxanthin are members of the xanthophyll family of carotenoids. Their concentration is particularly high in dark leafy green vegetables (Mares-Perlman et al., 2002). Part of what makes these compounds unique relative to other carotenoids in humans is that they are the only carotenoids present in the macula (a small area of the retina responsible for central vision and high visual acuity) and in the lens (Bone et al., 1985; Yeum et al., 1995). Observational studies in the US have suggested that lutein and zeaxanthin may be protective against certain eye diseases such as age-related cataracts and age-related macular degeneration and intervention studies showed that lutein supplementation resulted in improved visual function in patients suffering from these eye diseases and in increased lutein levels in the eye (Alves-Rodrigues and Shao, 2004).
In Lebanon, an Eastern Mediterranean country known for its richness and diversity in wild leafy edible greens but where the diet is characterized by a heavy reliance on refined grains as the primary source of energy (WHO, 1998), cataracts account for almost half of the causes of blindness (Mansour et al., 1997). The present
2.1 THE MEDITERRANEAN DIET AND FOOD DIVERSITYThe various cultures, religious beliefs, ecologic backgrounds and historic developments around the Mediterranean basin resulted in many diets that revolved around distinct local or regional traditions but also shared a multitude of elements.
Based on his observation of the food habits of some populations in the Mediterranean region, the American Ancel Keys was the first who described, in the 1960s, what was later to be known as the “Mediterranean diet” (Keys, 1980). The diet observed by Keys was based on a large variety of foods, mostly of vegetable origin, and characterized by a high consumption of fruits, vegetables, legumes, nuts, cereals and olive oil, and, on the other hand, a low consumption of meat and sausages. It’s this tremendous diversity that makes the Mediterranean diet unique and is also responsible for its numerous health benefits (Simopoulos, 2001).
As a matter of fact, dietary diversity is a crucial element of a high quality diet (Johns, 2003). Not only does it guarantee an adequate intake of nutrients but also it increases their bioavailability (Kennedy et al., 2003). Moreover, dietary diversity is thought, as well, to decrease the chances of both deficiency and excess and to decrease the likelihood that any food-borne toxicant will be consumed in hazardous amounts (IFT, 1975). Recently, a 10-country study conducted by Hoddinott & Yohannes (2002) using data from Ghana, Malawi, Mali, Kenya, India, the Philippines, Mozambique, Mexico, Bangladesh and Egypt, suggested that dietary diversity could also be a useful indicator of food security (defined as energy availability). Indeed, the results indicated that in each of these ten countries, there was a positive, significant association between household diet diversity and household calorie availability per capita.
32.2 WILD LEAFY GREENS AS FOOD
The diversity of the Mediterranean diet is a result of the high plant diversity of the Mediterranean region which, in fact, houses eleven of the world’s two hundred and thirty one most important centers for plant diversity, and approximately 25,000 species, of which about half are endemic (Heywood, 1999). Factually speaking, it’s the diversity of the Mediterranean region’s physical and climatic conditions that makes it one of the world's major centers of plant diversity and explains why a wide variety of edible wild plants are consumed and used in a range of ways in the Mediterranean diet all year round (Simopoulos, 2001).