Eye diseases
Based on WHO data [217], it is assumed that more than 28 million subjects in Europe are visually impaired, with a prevalence for blindness of 0.3 %. The main causes for loss of sight in Europe and the United States are age-related macular degeneration (AMD; 50 %), glaucoma (18 %), diabetic retinopathy (17 %), and cataract (5 %) [218]. Despite worldwide trends for reduced prevalence of visual impairment and blindness since the 1990s [219], the prevalence of eye diseases in the ageing population is expected to increase in Western countries, for example, Germany, within the next 20 years [220]. The prevalence is reported to be 3.5–40 % depending on age for AMD, 3.3–14 % for glaucoma, and 4.4–20.9 % for diabetic retinopathy [221]. The prevalence for cataract increases with age and is over 40 % in subjects older than 75 years [222–224].
Macular degeneration is an age-related degenerative retinal disease that leads to the loss of central vision [225]. Risk factors for the development of AMD include age, smoking, and nutrition [226–228]. Important protective factors are dietary fibre [229], mono-unsaturated fatty acids [230], certain vitamins [231–233], and especially carotenoids like lutein and zeaxanthin. These carotenoids selectively accumulate in the macula lutea (point of high-resolution vision) and protect the pigment epithelial cells from blue light and damage by short-wave rays [234].
The dietary intake of carotenoids, the serum levels, and the supplementation of these carotenoids are associated with a risk reduction for AMD in most of the studies [235–244]. While protective effects of a high lutein/zeaxanthin intake were observed, one study showed an increased risk of AMD at high β-carotene intake [244].
In an analysis of the NHS [245, 246] and in the prospective Rotterdam Study [247], the intake of lutein/zeaxanthin and other carotenoids was not associated with the risk of AMD. The results of the CHARM Study (Cardiovascular Health and Age-Related Maculopathy) indicate that at already existing AMD, high lutein/zeaxanthin intake can promote AMD progression [248].
Although lutein/zeaxanthin intake was calculated directly from food intake in the mentioned studies, hardly any studies have been published that have investigated the association between vegetable and fruit consumption and risk of AMD. In a prospective cohort study, the consumption of fruit, but not of vegetables, was associated with a risk reduction by 36 % [249]. In women younger than 75 years, the risk of AMD was reduced by 52 % at higher intake of vegetables (4 vs. 0.9 portions per day) [250]. High intake (>5 times/week) of foods rich in lutein, like spinach and collard greens, was associated with a reduction in the AMD risk by 86 % in a case–control study [251]. According to Goldberg et al. [252], the intake (>7 times/week) of vegetables and fruit rich in provitamin A was associated with a reduction in the AMD risk by 33 % in a cross-sectional study.
Cataract is a clouding of the lens in adults, which results in impaired vision or visual acuity [253]. The risk is influenced by age, ethnic origin, gender, smoking, sunlight, consumption of alcohol, diabetes mellitus, corticosteroid medication, and nutritional factors [254]. The data on the influence of vitamin C and carotenoids on risk of cataract are inconsistent [255–259]. The more recent results of the prospective Blue Mountains Eye Study [260] suggest that high intake of vitamin C, especially from fruit juices, is associated with a significantly reduced risk of cataract. The combined intake of vitamin C and other antioxidants (β-carotene, vitamin E, zinc) from foods and/or supplements was also associated with a reduction in the cataract risk by 38–49 %.
In 4 prospective cohort studies, the influence of vegetable and fruit consumption on risk of cataract was investigated. A diet according to the Dietary Guidelines for Americans 2000 is associated with a cataract risk reduction by more than 50 % [261]. In this subpopulation of the NHS, eating habits and cataract were investigated in 479 women between the age of 52 and 73 years. In the group with the highest fruit consumption (3.9 portions/day), the prevalence of cataract was 42 % lower than in the control group (1.3 portions/day). In the HPFS, high consumption of broccoli and spinach in men was associated with a reduction in the cataract risk by 23 and 27 % [262]. In participants of the Women’s Health Study, a high intake of vegetables and fruit was associated with a significant reduction in the cataract risk by 10–15 % [263]. In the updated analysis of the same study [264], the risk reduction (10 %) at high intake of vegetables and fruit was not significant any more (changed database and analysis). In contrast, in the highest quintile of both lutein/zeaxanthin and vitamin E intake, the risk of cataract was 18 % and 14 % lower than in the lowest quintile of intake. In the Carotenoids in the Age-Related Eye Disease Study (CAREDS), the risk was reduced by 26 % at high vegetable intake [265]. Comparing highest with lowest quintiles, the risk of cataract was reduced by 32 % regarding both the calculated daily intake of lutein and zeaxanthin and the measured plasma concentrations of lutein and zeaxanthin. These findings are confirmed by results of the prospectivePOLA Study (Pathologies Oculaires Liées à l’Age) [242]. In the group with the highest plasma concentration of zeaxanthin (≥0.09 μM), the risk of cataract was reduced by 43 % compared with the control group (<0.04 μM).
Glaucoma is caused by changes in the intraocular pressure that can damage the optic nerve and may progress to complete blindness [266]. There are hardly any data on the influence of lifestyle factors on the risk of glaucoma. Regarding nutritional factors, so far mainly the role of vitamins has been investigated [267,268]. Only one study described the association between vegetable and fruit intake and the risk of glaucoma [269]. In this cross-sectional investigation, a lowered risk was observed at high intake of certain kinds of vegetables and fruit, for example fresh carrots (−64 %).
Diabetic retinopathy is a microvascular complication of diabetes mellitus that is characterised by damage of the retina. Since it is a secondary disease of diabetes mellitus, there is a direct causal relation with the underlying primary disease [270, 271]. Currently, there are no studies available regarding the influence of the consumption of vegetables and fruit on the risk of diabetic retinopathy. Only in a small cross-sectional study from the Melbourne Collaborative Cohort Study, the association between the plasma concentration of carotenoids and the prevalence of diabetic retinopathy was investigated in 111 participants [272]. Type 2 diabetes patients with a diagnosis of diabetic retinopathy showed lower plasma concentrations of non-provitamin A carotenoids (lutein, zeaxanthin and lycopene) than patients without retinopathy.
Due to the low number of published studies, the evidence regarding the prevention of macular degenerationand cataract through higher consumption of vegetables and fruit is judged as possible. The evidence regarding the risk of glaucoma and diabetic retinopathy is insufficient due to the lack of data.
Dementia
Dementia is a clinical syndrome that is characterised by a decrease in intelligence, memory, and perception and may be caused by various diseases. Logical and critical thinking, judgement, retentive memory, and short-term memory are impaired, while remote memory (long-term memory) can remain for a long time. In addition, personality may deteriorate [273].
According to the latest Report of the European College of Neuropsychopharmacology and the European Brain Council, 6.34 million people in Europe aged at least 60 years were estimated to suffer from dementia in 2011, corresponding to a mean prevalence of 5.4 % in this population. The prevalence is age-dependent (1–30 %) and increases with advanced age [274]. Due to increasing life expectancy in industrialised countries and the exponential increase in dementia in old age, the prevalence of dementia in these countries will be rising steadily. At global level, with an incidence of 4.6 million per year, an increasing prevalence of dementia with 42 million cases in 2020 has also to be expected [275]. Thus, dementia has become one of the major challenges to public health [276].
Worldwide, Alzheimer’s disease and vascular dementia are the two most common subtypes of dementia, which account for 50–70 and 15–25 % of all dementia cases, respectively [276]. Old age and genetic susceptibility are well established risk factors for dementia and Alzheimers’s disease. Vascular risk factors (e.g. diabetes mellitus, hypertension, and smoking) as well as cardio- and cerebrovascular diseases may contribute to the development and progression of dementia, whereas social, physical, and mental activities may delay their onset [276]. Overweight increases the risk of dementia independent of comorbidities [277].
So far, only a few studies have investigated whether the consumption of vegetables and fruit is associated with the risk of dementia. In addition to dementia, the cognitive performance has also been used as target parameter by using certain tests that are sensitive enough to diagnose dementia (both vascular and Alzheimer‘s dementia) at an early stage [278].
Cross-sectional studies in Spain [279] and Korea [280] have shown that elderly people with good cognitive performance consumed more fruit and vegetables than elderly people with impaired or poor cognitive performance. For the Korean participants, these differences regarding vegetable and fruit consumption were only detected in women; in men, they were only found regarding fruit intake, but not regarding vegetable consumption [280]. Vegetable consumption, however, was comparable in both study populations (Korea: 248 g/day vs. Spain: 239 g/day). In
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