「安全」鉛含量仍與年輕成人的憂鬱及恐慌有關

作者：Janis C. Kelly  
出處：WebMD醫學新聞

　　December 9, 2009 — 新研究認為，血中鉛濃度較高的年輕成人比較可能有重度憂鬱症(major depressive disorder，MDD)或恐慌症，即便他們的鉛含量是一般所謂的安全範圍也是如此。
　　
　　加拿大蒙特婁大學、波士頓哈佛公共衛生學院的Maryse F. Bouchard博士等人發現，相較於鉛濃度0.7 μg/dL以下者，鉛濃度2.11 μg/dL以上者發生MDD的機會達2.3倍、發生恐慌症的機會將近5倍。
　　
　　Bouchard博士向Medscape Psychiatry表示，最令人驚訝的發現是，這麼低的鉛濃度仍與不佳的心智健康狀態有關，研究對象的平均血中鉛濃度為1.61 μg/dL。
　　
　　本研究登載於12月的一般精神醫學誌(Archives of General Psychiatry)。
　　
　　研究者分析在1999至2004年間參與「National Health and Nutrition Examination Survey」研究、年紀為20-39歲的1,987名成人的資料，參與者接受驗血等體檢，並完成診斷訪視，以確認MDD、恐慌症和廣泛性焦慮症。
　　
　　符合MDD診斷規範的有134人(6.7%)，44人(2.2%)有恐慌症，47人(2.4%)有廣泛性焦慮症。
　　
　　因為抽菸與血中鉛濃度有關，研究者進行附加分析以排除628名抽菸者。非抽菸者之中，相較於鉛濃度最低者，鉛濃度最高者的MDD風險增加2.5倍、恐慌症風險增加8.2倍。
　　
　　【需減少環境曝露】
　　Bouchard博士表示，以前對鑄造廠(或玻璃廠)、精鍊廠與電池工廠之工人進行的曝露量研究顯示，這些工人(血中鉛濃度平均為40 μg/dL)的憂鬱、敵意和焦慮症狀增加。
　　
　　對非職業曝露之年長者進行的研究顯示，血中鉛濃度較高者(平均6.3 μg/dL)的自認焦慮、畏懼焦慮和憂鬱的盛行率也較高。Bouchard博士表示，我的研究中，平均血中鉛濃度只有1.6 μg/dL，代表的是一般大眾的曝露程度。
　　
　　無鉛汽油減少了一般大眾的血中鉛濃度，但是，油漆、工業製程、製陶與水污染等依舊是鉛的曝露源。
　　
　　不過，Bouchard博士指出，血中鉛濃度反應的不只是最近的曝露，還代表過去的曝露，因為鉛會隱蔽在骨骼中慢慢地釋放進入血液。
　　
　　研究者結論表示，這些發現認為，鉛的神經毒性可能會造成不佳的心智健康，即使是一般認為的低濃度仍然會有風險。他們寫道，這些發現，以及最近在孩童研究的不良行為結果報告，都是類似的低血鉛濃度，強調須有減少環境鉛曝露方法的重要性。
　　
　　【質疑劑量-反應關係】
　　紐約羅徹斯特大學流行病學、社區與預防醫學小組代理主任Edwin van Wijngaarden博士為Medscape回顧此研究。
　　
　　他表示，雖然Bouchard博士等人報告的資料認為血中鉛濃度和重度憂鬱症之間有關聯，其劑量-反應關係還未確定，連含量最高的五分之一也沒有清楚的模式。
　　
　　作者們強調有統計上顯著傾向，如果這是真正的線性趨勢才是適當的，但是現在這種情況就不能確定。恐慌症和一般焦慮異常的結果，統計強度有限，使得統計上的風險估計不準確，對於這些結果的劑量-反應模式之詮釋，我會相當謹慎。
　　
　　van Wijngaarden博士也指出，只有對20-39歲的成人進行的這項心智健康研究結果，可能和累積鉛曝露劑量較高的年長者有所差異。
　　
　　van Wijngaarden博士等人最近在美國的一項研究中，檢視了人口為基礎的血中鉛濃度和憂鬱的關係，此一研究即將發表。
　　
　　加拿大健康研究中心以及國家環境健康科學研究中心支持本研究。Bouchard博士以及 van Wijngaarden博士皆宣告沒有相關財務關係。
　　
　　Arch Gen Psychiatry. 2009;66:1313-1319.


"Safe" Lead Levels Linked to Depression, Panic in Young Adults

By Janis C. Kelly
Medscape Medical News

December 9, 2009 — Young adults with higher blood lead levels are more likely to have major depressive disorder (MDD) or panic disorder, even if they have exposure to lead levels generally considered safe, new research suggests.

Maryse F. Bouchard, PhD, Universite de Montreal, Quebec, Canada, and Harvard School of Public Health, Boston, Massachusetts, and colleagues found individuals with lead levels of 2.11 μg/dL or more had 2.3 times the odds of having MDD and nearly 5 times the odds of panic disorder compared with those with lead levels of 0.7 μg/dL or less.

"What is most surprising is the finding that lead can be associated with adverse mental health status at such low levels of exposure," Dr. Bouchard told Medscape Psychiatry. The mean blood level in study subjects was 1.61 μg/dL.

The study is published in the December issue of Archives of General Psychiatry.

The investigators analyzed data from 1987 adults aged 20 to 39 years who were participants in the National Health and Nutrition Examination Survey between 1999 and 2004. Participants underwent medical examinations that included collection of a blood sample and also completed a diagnostic interview to identify MDD, panic disorder, and generalized anxiety disorder.

The number of individuals who met diagnostic criteria for MDD was 134 (6.7%), 44 (2.2%) had panic disorder, and 47 (2.4%) had generalized anxiety disorder.

Because smoking is related to blood lead levels, the researchers conducted additional analyses excluding the 628 smokers. Among nonsmokers, the elevation in risk between the highest and lowest blood lead levels was increased to 2.5-fold for MDD and 8.2-fold for panic disorder.

Need to Reduce Environmental Exposure

Previous studies conducted in highly exposed employees from foundries, smelters, and battery plants show that these workers (who had blood lead levels averaging 40 μg/dL) have reported elevated symptoms of depression, hostility, and anxiety, said Dr. Bouchard.

A study conducted in nonoccupationally exposed older men showed that those with higher blood lead levels (averaging 6.3 μg/dL) also had a higher prevalence of self-reported anxiety, phobic anxiety, and depression. "In my study group, the mean blood lead level was only 1.6 μg/dL, which is representative of the exposure level in the general population,” Dr. Bouchard said.

Eliminating lead from gasoline has decreased average blood lead levels in the general population, but remaining sources of exposure include paint, industrial processes, pottery, and contaminated water.

However, Dr. Bouchard pointed out that blood lead levels reflect not only current exposure but also past exposures because lead is sequestered in bones and is slowly released into the blood.

"These findings suggest that lead neurotoxicity may contribute to adverse mental health outcomes, even at levels generally considered to pose low, or no, risk," the researchers conclude. "These findings, combined with recent reports of adverse behavioral outcomes in children with similarly low blood lead levels, should underscore the need for considering ways to further reduce environmental lead exposures," they write.

Dose-Response Relationship Questioned

Edwin van Wijngaarden, PhD, interim chief of the Division of Epidemiology, Community & Preventive Medicine at the University of Rochester in New York, reviewed the study for Medscape.

"Although the data reported by Bouchard et al are certainly suggestive of an association between blood lead levels and major depressive disorder, the nature of the dose-response relationship is somewhat uncertain, with no clear pattern until the upper quintile.

"The authors emphasize the statistically significant trend statistics, which are appropriate if there is a true linear trend — not sure if that is the case here. The results for panic disorder and generalized anxiety disorder suffer from limited statistical power and consequently statistically imprecise risk estimates, and I would be cautious interpreting the dose-response patterns reported for these outcomes," he said.

Dr. van Wijngaarden also noted that the mental health outcomes studied were only available for adults aged 20 to 39 years and might differ for older adults with higher levels of cumulative lead exposure.

Dr. van Wijngaarden and colleagues recently examined population-based data on blood lead levels in relation to depression in the United States in a study that will be published in the near future.

This study was supported by the Canadian Institutes for Health Research and the National Institute of Environmental Health Sciences. Dr. Bouchard and Dr. van Wijngaarden have disclosed no relevant financial relationships.

Arch Gen Psychiatry. 2009;66:1313-1319.