远见性饮食

随着年纪的增长，人的视力会逐渐下降，您对此无能为力？大错特错！这一流传已久的谣言已被最近的研究成果揭穿。实际上，饮食对年纪增长后是否会遭受视力下降有着极大影响。

您对自己眼部的关注是正确的。在全球视力下降三大首要原因中，白内障和黄斑变性占据了两位。例如，全球有1.96亿人患有黄斑变性，这一数字到2040年预计将增加到2.88亿。您想的也没错，这些造成视力下降的原因的确会随着我们年纪的增长而增加。比如，白内障是一种因眼内晶状体浑浊导致视力受损的疾病，在老年群体中非常普遍。超过半数的美国人到了80岁不是患有白内障，就是曾经接受过白内障手术。黄斑变性由视网膜中心部分退化导致。视网膜是一层位于眼球内部后层的薄膜，用来记录我们看到的图像，并通过视神经将图像由眼部传输至大脑。这种疾病同样在老年人中最为常见，这恰恰说明了它为什么又被称为老年性黄斑变性（ARMD或AMD）。(1, 2)

请考虑一下这个问题：视力下降仅仅是因为上了年纪，还是由我们在生活中做出的选择所致（至少在某种程度上）？众所周知，食用大量颜色丰富的水果和蔬菜的人黄斑色素(MP)流失的风险最低，而黄斑色素与老年性黄斑变性(ARMD)是相互关联的。例如，饮食中含有大量蔬菜、豆类、水果和海鲜的人群患老年性黄斑变性(ARMD)的风险要低41%，而那些拥有典型美式饮食习惯，食用富含脂肪的奶制品、肉类、薯条、添加糖份和精细谷物的人群患病风险则要高出2倍。(3)

研究将饮食和患病的关联进一步细化，一些特定的营养物质成为关注的中心。由美国国家眼科研究所出资进行的年纪相关眼部疾病研究(AREDS)发现，每日从健康饮食中摄取的特定抗氧化剂以及存在于多脂鱼类中的omega-3脂肪，可能有助于减缓随年纪增长而造成的视力下降。(4)

这些营养物质如何保护视力？

1) 维他命C和E等抗氧化剂可以保护眼部免受紫外线辐射造成的损伤。当眼部暴露于强光之下时，强光会产生被称为“自由基”的小型氧碎片，它们会损坏膜壁。因此，眼部受到此类损伤的情况极为普遍。眼部会自发地储存高于血液含量20倍甚至更多的维他命C。眼组织中的高浓度维他命C可能是一种用来防御太阳光中有害紫外线的适应性表现。每日摄入至少500毫克的维他命C和400IU的维他命E似乎对维持这些维他命的最佳组织水平最为有效。(5)

2) 叶黄素和黍黄素虽然是抗氧化剂，但其作用远不止于此。这两种复合物可穿过血-脑屏障以及血-视网膜屏障，在眼部形成黄斑色素(MP)。它们如同内置的太阳镜一样，会吸收损害黄斑并导致老年性黄斑变性(ARMD)的蓝光。每天仅需摄入10毫克的叶黄素以及2毫克的黍黄素（相当于1/2杯煮熟菠菜中的含量），便可提高血液和眼组织的叶黄素水平并降低视力下降的风险。(6) 在大量摄入叶黄素和黍黄素情况下，视力问题即使出现也不大可能进一步恶化。

3) omega-3脂肪DHA是存在于眼组织中的主要omega-3脂肪。这种脂肪可提高膜的流动性，并让细胞更易于控制物质的进出。它也具有抗炎症和免疫刺激的功能。作为一种十分重要的脂肪，它支持眼内液从眼部正常排出，从而降低高眼压和青光眼的风险。初步证据显示，海鲜中的DHA和EPA这两种omega-3可能对一种称为“干眼症”的病情起到缓解作用。(7, 8)

远见性饮食十分简单，只需按照以下指南安排有利于视力健康的食品即可： 

1.每日至少摄入9份颜色丰富的新鲜水果和蔬菜（包括2份富含叶黄素的深绿色叶类蔬菜以及2份富含维他命C的柑橘类水果）。 

2.通过减少食用肉类和富含脂肪的乳制品来限制或避免饱和脂肪的摄入，重点摄入鱼类身上对眼部健康有益的脂肪，选择添加了以海藻为提取物的DHA(life'sDHA)的食物，并/或服用含至少220毫克DHA Omega-3的补充剂。

3.即便您的饮食结构已趋于完美，但仅通过饮食的摄入量依然难以完全获取可预防视力下降的营养物质。您可以考虑服用补充剂来补充营养方面的不足。寻求各类高质量的补充剂，包括含有叶黄素、黍黄素的补充剂。

4.全年佩戴防护性太阳镜，以完全过滤阳光中的紫外线。

5.及早发现任何视力下降的征兆。在20岁到30岁之间让医生为您进行至少一次散瞳后的检查，在30岁到40岁之间进行两次检查，在40岁到64岁之间每2到4年进行一次检查，此后每1到2年进行一次检查。

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2.Wong W, Su X, Li X, et al.Global prevalence of age-related macular degeneration and disease burden projection for 2020 and 2040: a systematic review and meta-analysis.The Lancet Global Health.2014;2(2):e106-e16.

3.Chew E:Nutrition effects on ocular disease in the aging eye.Investigative Ophthalmology & Visual Science 2013;54:(14):ORSF42-7.

4.The AREDS study’s findings: https://nei.nih.gov/amd/summary#1

5.The Age-Related Eye Disease Study 2 Research Group: lutein + zeaxanthin and omega-3 fatty acids for age-related macular degeneration.Journal of the American Medical Association 2013;309:2005-2015.

6.Chew E, Clemons T, Agron E, et al:Long-term effects of vitamins E and E, beta carotene, and zinc on age-related macular degeneration:AREDS report no. 35.Ophthalmology 2013;120:1604-1611.

7.Gatell-Tortajada J:Oral supplementation with a nutraceutical formulation containing omega-3 fatty acids, vitamins, minerals, and antioxidants in a large series of patients with dry eye symptoms.Clinical Intervention in Aging 2016;11:571-578.    

8.McCusker M, Durrani K, Payette M, et al:The role of vitamins, essential fatty acids, and antioxidants in age-related macular degeneration, dry eye syndrome, and cataracts.Clinical Dermatology 2016; 34:276-285.

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