Eating oily fish has long been hailed as a way to keep brains active and cut the risk of a stroke.
But now U.S. scientists beileve eating the fish and nuts might not act as a brain boost after all.
Contrary to previous research, the latest suggests that omega-3 fatty acids, found in fish such as salmon and in nuts, may not halt the decline in brainpower.
Study author Eric Ammann of the University of Iowa, said: 'There has been a lot of interest in omega-3s as a way to prevent or delay cognitive decline, but unfortunately our study did not find a protective effect in older women.
'In addition, most randomised trials of omega-3 supplements have not found an effect.
'However, we do not recommend that people change their diet based on these results
Past studies have credited oily fish with the ability to cut post-natal depression, reduce the risk of Altzheimer's disease and diabetes, stroke and arthritis as well as help children perform better in exams and even add two years' to a person's life expectancy.
Mr Ammann said: 'Researchers continue to study the relationship between omega-3s and the health of the heart, blood vessels and brain.
'We know that fish and nuts can be healthy alternatives to red meat and full-fat dairy products, which are high in saturated fats.'
The study, published in the journal Neurology, involved 2,157 women age 65 to 80 who were enrolled in the Women's Health Initiative clinical trials of hormone therapy.
The women were given annual tests of thinking and memory skills for an average of six years.
Blood tests were taken to measure the amount of omega-3s in the participants' blood before the start of the study.
The researchers found no difference between the women with high and low levels of omega-3s in the blood at the time of the first memory tests.
There was also no difference between the two groups in how fast their thinking skills declined over time.
新闻资讯：
三文鱼和坚果因其所含有的Omega-3 不饱和脂肪酸而被认为是健脑佳品。但《神经学》杂志近日发表的一篇研究报告表明它们并不能延缓大脑衰老，增强脑力。
科学家们对2157位年龄在65至80岁的妇女进行了测试。她们都参加了激素治疗的临床测试，并且在六年的时间里，每年都进行思维和记忆力的测试。在研究 开始前，她们都验了血以便获知Omega-3 脂肪酸在血液里的含量。该研究发现测试者记忆能力的强弱与体内的Omega-3 脂肪酸的含量高低没有关系，并且她们思维能力的衰退快慢也与Omega-3 脂肪酸的含量高低没有关系。
该研究报告的作者，艾奥瓦大学的埃里克安曼说：“很多人认为Omega-3 不饱和脂肪酸可以延缓认知能力的衰退，所以鱼类和坚果成为替代红肉等富含饱和脂肪酸的食物的健康选择。但我们通过对老年妇女的研究发现该物质在这方面没起 多大作用。并且，随机测试表明Omega-3补充剂也同样无效。英语作文
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