不飽和脂肪酸Omega-3可以預防老年性視覺損失

美國國家眼科學院一份新的研究指出，增加不飽和脂肪酸Omega-3的攝取可以降低30%的老年性盲眼罹患率。

在老年性眼部疾病研究(Age-Related Eye Disease Study--AREDS)的一個分類裡有提到: 服用omega-3可以預防老年性黃斑性病變--AMD(50歲以上的人眼盲的主要原因)。AMD是一種退化性視網膜疾病，以致中央視力逐步受損，僅剩周邊視力。根據AMD國際聯盟指出，在西方國家，這種眼疾多在五十五歲之後發病。

聯盟指出，雖說在全世界大約有2千5百萬至3千萬人患有AMD，但對AMD的認識仍是很低。當嬰兒潮世代成長之後，聯盟預估在2025年AMD的罹患率會攀升至3倍。AMD有乾濕兩種類型。濕型老年黃斑病變發生在視網膜下不正常的血管增生。這些新生血管最終會滲出液體或出血，造成視網膜剝離而影響視線。乾型的則是視網膜裡正常的組織漸漸消失，造成視網膜白化稱” 中間地圖狀萎縮(Central gerographic atrophy)”。

建構Omega-3對眼睛的益處

Omega-3脂肪酸(特別是DHA)在視網膜神經細胞膜中扮演著重要的角色，並有研究指出omega-3可以保護AMD的發生。事實上，一份在2008年六月發表的眼科檔案(Archives of Ophthalmology)中指出，經過整合分析後發現攝取大量的omega-3脂肪酸還有魚類可以降低罹患AMD的風險達38%。而在澳洲墨而本大學的科學家則指出DHA所帶來的益處對晚期的AMD有明顯的改善，而每周吃於兩次則對早期和晚期的AMD有降低風險。

資料來源: American Journal of Clinical Nutrition

生資有限公司摘譯/ by Amy

Omega-3 may prevent age-related sight loss

Increased intakes of omega-3 fatty acids may reduce the risk of developing age-related blindness by 30 per cent, says a new study from the US National Eye Institute.

A subsection of the Age-Related Eye Disease Study (AREDS) supported the beneficial effects of omega-3 consumption for preventing age-related macular degeneration, the leading cause of blindness in the over 50s.

“If these results are generalizable, they may guide the development of low-cost and easily implemented preventive interventions for progression to advanced age-related macular degeneration,” wrote the researchers, led by John Paul SanGiovanni.

Eyes on AMD

AMD is a degenerative retinal disease that causes central vision loss and leaves only peripheral vision. It is the leading cause of legal blindness for people over 55 years of age in the Western world, according to AMD Alliance International.

Despite the fact that approximately 25 to 30 million people worldwide are affected by AMD, awareness of the condition is low, says the Alliance. And as the generation of Baby Boomers gets older, the Alliance expects incidence to be on the rise and triple by 2025.

There are two types of AMD – wet and dry. The former occurs when blood vessels grow abnormally beneath the macular (neovascular AMD). The blood vessels eventually leaks and the macular is scarred, obscuring vision. Dry AMD occurs when normal tissue in the macula slowly disappears. This results in a pale area of the macular called central geographic atrophy.

Increased intakes of omega-3 fatty acids may reduce the risk of both wet and dry AMD by 35 and 32 per cent, respectively, according to findings published online in the American Journal of Clinical Nutrition.

Building omega-3’s eye benefits

It is known that omega-3 fatty acids, and particularly DHA, play an important role in the layer of nerve cells in the retina, and studies have already reported that omega-3 may protect against the onset of AMD.

Indeed, a meta-analysis published in the June 2008 issue of the Archives of Ophthalmology found that a high intake of omega-3 fatty acids and fish may reduce the risk of AMD by up to 38 per cent. Scientists from the University of Melbourne in Australia reported that the benefits were most pronounced against late (more advanced) AMD, while eating fish twice a week was associated with a reduced risk of both early and late AMD.

The new study supports these earlier findings. SanGiovanni and his co-workers looked at a sub-section of 1,837 people participating in the phase 3 Age-Related Eye Disease Study (AREDS). All the participants were considered to be at a moderate-to-high risk of advanced AMD.

Over 12 years of study, the researchers found that intakes of omega-3, estimated using a food-frequency questionnaire, were related to both wet and dry AMD risk.

Indeed, participants with the highest omega-3 intakes, equivalent to about 0.11 per cent of their total energy intakes, had a 30 per cent lower risk of developing both types than people with the lowest intakes.

“The 12-year incidence of central geographic atrophy and neovascular AMD in participants at moderate-to-high-risk of these outcomes was lowest for those reporting the highest consumption of omega-3 fatty acids,” concluded the researchers.

Being an observational study, the researchers did not consider the mechanism. However, an earlier mouse study partly funded by the National Eye Institute noted lower levels of inflammatory molecules, such as prostaglandin E2 and leukotriene B4, and higher levels of anti-inflammatory molecules, such as prostaglandin D2 (American Journal of Pathology, Vol. 175, pp.799-807).

Published online ahead of print, doi:10.3945/ajcn.2009.27594
“Omega-3 Long-chain polyunsaturated fatty acid intake and 12-y incidence of neovascular age-related macular degeneration and central geographic atrophy: a prospective cohort study from the Age-Related Eye Disease Study”
Authors: J.P. SanGiovanni, E. Agron, A.D. Meleth, G.F. Reed, R.D. Sperduto, T.E. Clemons, E.Y. Chew