June 30, 2008 -- Low levels of high-density lipoprotein (HDL), or "good" cholesterol, in middle age could increase the risk of developing dementia later in life, new research suggests.

Falling HDL cholesterol levels among study participants in their mid 50s to early 60s predicted memory declines during the same period.

Although poor memory in middle age has not been directly linked to Alzheimer's disease and other forms of dementia in old age, memory decline is key to the diagnosis of these conditions, lead researcher Archana Singh-Manoux, PhD, tells WebMD.

"Our research does not show a link between HDL and dementia," she says. "We looked at cognitive decline in midlife, but it may turn out that this decline is a risk factor for dementia."

HDL, LDL and Memory
Researchers have attempted to study HDL and other lipids like low-density lipoprotein (LDL), total cholesterol, and triglycerides in patients with Alzheimer's and other age-related dementias, but these studies have proven problematic, Singh-Manoux says.

"By the time people are diagnosed they have usually had the disease for many years, and the disease itself may have modified these lipid profiles," she says.

As a result, more and more researchers are focusing on potential risk factors for dementia that present long before the disease is identified.

This was the approach used by Singh-Manoux and colleagues from the University College London.

Their study included 3,673 civil servants enrolled in a British health trial, which included periodic analysis of blood lipid levels and testing for memory declines.

The data analyzed by the researchers were collected at two time periods -- when the average age of the participants was 55 and again when they were 61.

Low HDL cholesterol was defined as less than 40 mg/dL, and an HDL level of 60 mg/dL or more was considered high.

During the observation period, declines in HDL were found to be associated with corresponding declines in memory.

At age 61, study participants with low levels of "good" cholesterol had a 53% increased risk of memory loss compared to participants with high HDL levels.

Statins Didn't Help Memory
Total cholesterol and triglyceride levels were not linked with memory declines, and the use of statin drugs did not seem to affect memory loss.

Statins lower LDL but are not very effective for raising HDL. Clinical trials of other drugs that specifically target HDL have so far proven disappointing.

Following a healthy lifestyle -- including regular exercise, maintaining a healthy weight, and not smoking -- is the best way to raise HDL levels, American Heart Association (AHA) spokeswoman Martha Daviglus, MD, PhD, tells WebMD.

"A healthy lifestyle can make a huge difference for everyone," she says. "We know that lifestyle is key to lowering risk for a whole range of diseases and conditions."

The new findings suggest that making healthy lifestyle choices early on could benefit memory and cognitive function in middle age with the possibility of preventing dementia later in life.

The study appears in the August issue of the AHA journal Arteriosclerosis, Thrombosis and Vascular Biology.

"Total cholesterol and LDL are well established risk factors for heart disease," Singh-Manoux says. "Physicians monitor these levels regularly, but I don't think we pay enough attention to HDL cholesterol. Our results show HDL cholesterol to be important for memory, so physicians and patients should be encouraged to monitor HDL."

2008年6月30日-一項新的研究表明,中年時體內高密度脂蛋白即“好”膽固醇濃度降低能增加后半生患癡呆癥的風險。

受試者年齡在55歲左右至60歲出頭,他們體內高密度脂蛋白膽固醇濃度的下降預測了同期記憶力的下降。

盡管中年時記憶力差與老年時患阿茨海默氏病和其他形式的癡呆癥沒有直接相關,但記憶力下降對這些病的診斷至關重要,領導這項研究的Singh-Manoux博士對WebMD表示。

“我們研究并沒有表明高密度脂蛋白和老年癡呆有關”,她說:“我們觀察到中年時有認知能力下降,但是可以證明記憶力下降是癡呆癥的一個風險因素。”

高密度脂蛋白低密度脂蛋白和記憶
研究人員試圖對患阿茨海默氏病和與年齡相關癡呆癥病人中的高密度脂蛋白及其它脂類如低密度脂蛋白、總膽固醇和肝油三脂等進行研究。但這些研究由于問題諸多而很難開展,Singh-Manoux說。

“在確診之前,病人通常已患癡呆病多年,并且這種疾病本身可以改變脂蛋白特性,”她說。

最終,越來越多的研究人員開始關注癡呆癥潛在的風險因素,因為在疾病確診之前,這些風險因素就有表現。

倫刻大學Singh-Manoux和她的同事就采用了這種方法,

他們的這項研究有3673例公務員,為一項英國健康試驗的受試者。受試者需定期進行血脂檢驗和記憶力下降的測試。

研究人員分析的數據主要來自兩個時間段,受試者平均年齡在55歲時,以及之后在他們到61歲時。

高密度脂蛋白膽固醇低濃度定義為濃度低于40 mg/dL,而高濃度則為60 mg/dL以上。

研究人員觀察期間發現高密度脂蛋白下降與相應記憶力的下降有關。

在平均年齡在61歲時,與體內高濃度的高密度脂蛋白的受試者相比,體內低濃度“好”膽固醇的受試者記憶力喪失的風險增加53%。

他汀類藥物無助于記憶。

總膽固醉和肝油三脂的濃度與記憶力減退無關,應用他汀類藥物似乎不影響記憶喪失。

他汀類藥物降低低密度脂蛋白但對升高高密度脂蛋白沒有明顯效果,迄今為止,其他針對高密度脂蛋白的臨床試驗令人失望。

培養健康的生活方式-包括定期鍛煉,保持體重,戒煙,這是升高高密度脂蛋白最好方法,美國心臟病協會發言人醫學博士Martha Daviglus對WebMD表示。

“健康的生活方式能使每個人發生巨大變化”,她說,“眾說周知,生活方式對降低各種疾病和不良狀態的風險至關重要。

這項新的研究表明,早期養成健康的生活方式能改善中年時記憶力和認知功能,并可能預防后半生患癡呆癥。

這項研究發表在美國心臟病協會《動脈硬化血栓血管生物學形成》8月期刊上。

“總膽固醇和低密度脂蛋白已確認為心臟病的風險因子,”Singh-Manoux說。“醫生定期對這兩項指標進行檢測,但是我認為我們并沒有對高密度脂蛋白給予足夠的重視,我們研究結果表明高密度脂蛋白對記憶非常重要,因此醫生和病人應當進行高密度脂蛋白的監測。”