People with age-related macular degeneration （AMD） should eat oily fish at least twice a week to keep their eye disease at bay, say scientists.

Omega-3 fatty acids found in abundance in fish like mackerel and salmon appear to slow or even halt the progress of both early and late stage disease.

The researchers base their findings on almost 3,000 people taking part in a trial of vitamins and supplements.

The findings are published in the British Journal of Ophthalmology.

An estimated 500,000 people in the UK suffer from AMD, which destroys central vision.

Protective

Experts have already suggested omega-3 may cut the risk of getting AMD by a third, and now this latest work suggests these fats also benefit patients who already have the disease.

Progression to both dry and wet forms of advanced AMD disease was 25% less likely among those eating a diet rich in omega-3 fatty acids.

People with advanced AMD who also consumed a low-GI diet, eating of foods that release their sugar more slowly, and who took supplemental antioxidant vitamins and minerals like vitamin C and zinc appeared to reduce their risk of disease progression by even more - by up to 50%.

Substituting five slices of wholegrain bread for white bread every day out of a total intake of 250g of carbohydrate might cut out almost 8% of advanced age related macular degeneration over five years, say the authors.

Surprisingly, however, the supplements were counterproductive for those with early AMD, negating the benefits of omega-3 fats, and even appeared to increase the risk of disease progression.

Those who took all the antioxidant vitamins plus zinc, and who a high daily intake of beta carotene - found in yellow and green vegetables - were 50% more likely to progress to advanced disease.

The researchers at Tufts University, Boston, believe omega-3 fatty acids offer protection against AMD by altering fat levels in the blood after a meal that can be damaging to the body.

'Moderation'

But they say it is not clear whether patients should also consider taking supplements as well as omega-3 because of their mixed findings.

They suggest that eating two to three servings of fatty fish, such as salmon, tuna, mackerel, shellfish, and herring every week, would achieve the recommended daily intake （650mg） of omega-3, substantially cutting the risk of both early and late stage AMD.

The UK's Food Standards Agency says people should eat at least two portions of fish a week including one of oily fish.

But they caution that too much oily fish is bad because it can contain low levels of pollutants that can build up in the body.

Most people can safely eat up to four portions a week, but girls and women who might have a baby and those who are pregnant or breastfeeding should limit their intake to two portions a week.

A spokeswoman from RNIB said good nutrition was very important for both general and eye health.

"These findings appear to be consistent with previous research that has shown that eating omega-3 poly-unsaturated fats as part of a balanced diet may help prevent the development of age-related macular degeneration, the main cause of severe sight loss in the UK.

"RNIB hopes that this will further highlight why looking after your eyes should be a key motivation in maintaining a healthy lifestyle," she said.

科学家表示，患有老年性黄斑病变（AMD）眼疾的人，每星期至少要进食含油脂性的鱼两次，以保持眼睛健康。

科学家在鱼类如鲭鱼及三文鱼中发现大量的奥米加-3（Omega-3）脂肪酸，这些脂肪酸可以纾缓，甚至抑止眼疾初期及中期的扩展。

研究员的研究结果是根据差不多3千名参加食用维他命及补充营养试验的人得出来的。

英国眼科期刊（British Journal of Ophthalmology）已刊登这项研究结果。

英国估计约有50万人患有会破坏中央视力的老年性黄斑病变。

具保护作用

专家早现表示奥米加-3可以减去患老年性黄斑病变三分之一分的机会，而今次这项研究显示，这脂肪酸对于已患上这眼疾的病人，同样奏效。

干性及湿性的中期老年性黄斑病变患者，饮食中含丰富奥米加-3脂肪酸，均减低病情25%.

而患中期老年性黄斑病变的人，饮食中采用低GI值，吃一些释放糖份较慢的食物，并进食补充抗氧维他命及矿物质，如维他命C及锌，他们病情改善高达五成，情况明显。

发表研究的作者们说，每天以五片全麦面包代替白面包，可取得共250克碳水化合物，五年内可减去老年性黄斑病变8%.

但最让人感到惊讶的是，补充营养对初期老年性黄斑病变却有反效果，会抵销奥米加-3脂肪酸的果效，甚至似乎会令病情加重。

一些进食抗氧维他命及锌，和每天食用含大量胡萝卜素的黄色及绿色蔬菜，有五成机会令病情变重。

波士顿培夫斯（Tufts）大学的研究员认为，于餐后，奥米加-3脂肪酸能更改血液中的脂肪水平，以保护及对抗老年性黄斑病变。

"中庸之道"

但是由于研究结果混合多种情况，他们表示不太肯定病人应否同时食补充营养和奥米加-3.

他们建议每周食用两至三份油脂丰富的鱼，如三文鱼，吞拿鱼，鲭鱼，贝类及鲱鱼，便可获得每天建议食量（650毫克）的奥米加-3脂肪酸，大大减低早期及中期老年性黄斑病变的风险。

英国食品标准署（The UK's Food Standards Agency）表示，人们应每周进食至少两份鱼，其中一份应包括含高油脂的鱼。

但他们警戒道，食用过量的含高油脂鱼会有损健康，因为这些鱼中含有低水平的污染物，这些污染物会在体内积聚。

大部分的人可放心一周进食四份含油脂的鱼，有怀孕机会的女孩及妇女，孕妇及喂哺母乳的则应限制食量至一周两份。

（英国）皇家全国盲人协会（RNIB）发言人表示，充足营养对身体及眼睛健康都十分重要。

「这些发现与之前研究显示把奥米加-3多元不饱和脂肪酸作为均衡饮食一部份，有助预防老年性黄斑病变的结果一致，这疾病在英国是导致失明的主要成因。」

她说：「皇家全国盲人协会希望今次进一步令大家明白，照顾双目是保持健康生活一个重要源动力。」