牛奶中的农药与低神经元密度有关


  【24drs.com】根据一篇新研究,1980年代初期在牛奶中发现该年代之前使用的一种农药,可能和巴金森氏症患者脑部的神经退化结果有关。
  
  这篇由日本大津滋贺医科大学Robert Abbott 博士所领衔的研究,在线发表于12月9日的神经学期刊。
  
  他解释,之前认为摄取乳制品和巴金森氏症有关,不过原因未知。有机氯农药也被认为与巴金森氏症有关,我们的研究结果认为,牛奶中的农药和巴金森氏症者的神经退化可能有关。
  
  这篇研究提到的农药—环氧化七氯(heptachlor epoxide) —目前在西方世界已不再使用,但是,Abbott 博士强调,这是一个非常持久的化学药品,会被土壤与水吸收,在环境中停留数年。所以它会出现在鱼类和牛乳中,它最近在许多国家被发现,大多是在较少控制的发展中国家。
  
  他还指出,这篇研究已经超越了使用这一特定杀虫剂的广泛影响。
  
  我们知道,巴金森氏症患者的饮食很重要。现在,我们发现,饮食和黑质的神经退化有关,更重要的是,多年前的饮食习惯和后来的脑部变化有关,这表示,要防止这些变化发生的所需时间相当长。
  
  另外,我们要对我们所饮所食有所认识。这篇研究探讨牛奶,但是,我们该考虑的不只是牛奶。宏观背景是,这项研究认为,脑部因巴金森氏症而发生变化时,多年之前的环境因素依旧有影响。我们吃的、喝的、呼吸的一切,都会影响多年后的脑部情况。
  
  为了进行本篇研究,来自夏威夷的449名日裔美籍男性(平均年龄54岁)参与檀香山亚洲老化研究,追踪超过30年,直到死亡,死后进行尸检。
  
  牛奶摄取资料搜集期间为1965-1968年,尸检是在1992-2004年间进行,测量黑质的神经元密度。研究者也检测116名男性之脑组织的环氧化七氯值。这个农药在1980年代之前被广泛用于夏威夷,且在1980年代初期于夏威夷供应的牛奶中的含量过高。
  
  结果显示,喝大量牛奶(>16盎司/天)之非抽菸者的神经元密度最低,Abbott 博士指出,之前有研究认为抽菸与巴金森氏症风险较低有关。
  
  排除路易氏体失智症或巴金森氏症案例之后,校正所有人的神经元密度,喝大量牛奶(>16盎司/天)者的背内侧象限值,比喝较少量者低41.5% (P = .001)。对于曾经在某个时间点抽菸者,喝牛奶和神经元较少无关。
  
  喝最多牛奶的人之中,90%的脑中测出环氧化七氯残留,没有喝牛奶者则是有63%测出。
  
  Abbott博士指出,这篇研究有若干假设。他表示,牛奶摄取量是在1960年代报告,我们假设牛奶摄取模式在往后几年会是相同的。我们并没有测量牛奶中的环氧化七氯量,所以,我们无法确切地说牛奶有被农药污染,但是,那些喝最多牛奶者的脑部尸检发现,脑中有这个农药。
  
  他指出,研究的重要讯息是,在巴金森氏症被诊断之前,我们可以预测脑中重要区域的细胞死亡和巴金森氏症有关,我们也可以追踪在这状况下所见的神经元退化。
  
  纽约州纽约市哥伦比亚大学Karen Marder医师、北卡罗莱纳州三角研究园区、国家环境健康科学研究中心的Honglei Chen医师在编辑评论中指出,虽然牛奶遭受环氧化七氯污染是这些研究结果的合理解释,但是,这篇研究没有直接显示脑中的环氧化七氯是来自牛奶而非其它来源。
  
  他们指出,这篇研究认为环氧化七氯污染是夏威夷最常喝牛奶者的巴金森氏症风险比较高的罪魁祸首,但是,它并未在其它世代提供摄取牛奶或乳制品与巴金森氏症之关联的良好解释 ,而且,牛奶污染的证据不足。
  
  但是,编辑们结论指出,这篇研究为流行病学研究如何探讨巴金森氏症的因果机转设定了一个良好范本,应该鼓励这种以终身方式追踪探讨、揭开神经退行性疾病之复杂过程的方法。
  
  资料来源:http://www.24drs.com/
  
  Native link:Pesticide in Milk Linked to Lower Neuron Density

Pesticide in Milk Linked to Lower Neuron Density

By Sue Hughes
Medscape Medical News

A pesticide used before the early 1980s and found in milk at that time may be associated with neurodegenerative findings in the brain characteristic of Parkinson's disease, according to a new study.

The study, published online in Neurology on December 9, was led by Robert Abbott, PhD, Shiga University of Medical Science in Otsu, Japan.

"Consumption of dairy products has been linked to Parkinson's disease before but a reason for this is not known," he explained to Medscape Medical News. "Organochlorine pesticides have also been linked to Parkinson's. Our results suggest that pesticides in the milk may be related to the neurodegeneration seen in Parkinson's."

This pesticide in this study — heptachlor epoxide — is not used anymore in the western world, but Dr Abbott stressed that it is a very persistent chemical that is absorbed into the soil and water and stays in the environment for many years.

"So it can still end up in fish and milk. It has recently been detected in several countries and is probably more prevalent in developing countries, where there are fewer controls," he said.

Long Window of Opportunity

He also makes the point that this study has wider implications beyond the use of this one particular pesticide.

"We know diet is important in Parkinson's. We have now shown that diet is linked to neurodegeneration in the substantia nigra, and more importantly, dietary habits many years earlier are linked to later changes in the brain," he said. "This suggests there is a long window of opportunity where it may be possible to prevent these changes from occurring."

He added: "The other message is that we need to be aware of what we are eating and drinking. This study has looked at milk but it is not just milk we should think about. The big picture is that this study suggests an environmental factor can predate brain changes typical of Parkinson's long before the condition ever develops. What we eat/drink/breathe may affect what happens in our brains years later."

For the study, 449 Japanese-American men (average age, 54 years) from Hawaii who participated in the Honolulu-Asia Aging Study were followed for more than 30 years until death, after which autopsies were performed.

Milk intake data were collected from 1965 to 1968. Postmortem examinations were conducted between 1992 and 2004. Neuron density counts in the substantia nigra were measured. The researchers also tested brain tissue from 116 men for levels of heptachlor epoxide, which was used extensively in Hawaii before the 1980s and was found at excessively high levels in the milk supply in Hawaii in the early 1980s.

Results showed that neuron density was lowest in nonsmokers who consumed high amounts of milk (>16 oz/day). Dr Abbott noted that smoking has previously been associated with a lower risk for Parkinson's.

After removing cases of Parkinson's or dementia with Lewy bodies, adjusted neuron density in all but the dorsomedial quadrant was 41.5% lower for milk intake greater than 16 oz/day vs lesser intake (P = .001). For persons who were smokers at any point, there was no association between milk intake and loss of neurons.

Among those who drank the most milk, residues of heptachlor epoxide were found in 90% of brains as compared with 63% of those who consumed no milk.

Assumptions

Dr Abbott noted that several assumptions were made in this study.

"The consumption of milk was reported in the 1960s, and we are assuming the pattern of milk consumption would have stayed the same in the years ahead," he said. "And we didn't measure levels of heptachlor epoxide in the milk, so we can't actually say for sure that the milk was contaminated with the pesticide, but brains at autopsy did contain this pesticide at higher amounts in the patients who drank the most milk."

He added: "The important messages from our study are that we can predict cell death in critical regions of the brain associated with Parkinson's before the condition is diagnosed and that dietary factors can predate the clinical symptoms of Parkinson's and can track with the neurodegeneration seen in the condition."

In an accompanying editorial, Honglei Chen, MD, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, and Karen Marder, MD, Columbia University, New York, New York, point out that although contamination of milk with heptachlor is a reasonable explanation for the findings, the study did not directly show that the brain heptachlor was from milk rather than from other sources.

They add that the current study makes heptachlor contamination a plausible culprit for higher Parkinson's disease risk among frequent milk drinkers in Hawaii, but it may not offer a good explanation for the association of milk or dairy consumption and Parkinson's in other cohorts where evidence of milk contamination is lacking.

But the editorialists conclude that the study "sets an excellent example of how epidemiologic studies can contribute to the search for causal mechanisms underlying PD [Parkinson's disease]," adding that "this life-course approach to unveiling the complicated process of neurodegeneration should be encouraged."

The study was supported by a contract and grants from the National Institute on Aging; by a contract from the National Heart, Lung, and Blood Institute; by a grant from the National Institute of Neurological Disorders and Stroke; by a grant from the United States Department of the Army; by the Office of Research and Development, Medical Research Service, Department of Veterans Affairs; by the Kuakini Medical Center; and in part by the Intramural Research Program of the National Institute on Aging. The authors have disclosed no relevant financial relationships.

Neurology. Published online December 9, 2015.

    
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