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-一项新的研究表明,中年时体内高密度脂蛋白即“好”胆固醇浓度降低能增加后半生患痴呆症的风险。

受试者年龄在55岁左右至60岁出头,他们体内高密度脂蛋白胆固醇浓度的下降预测了同期记忆力的下降。

尽管中年时记忆力差与老年时患阿茨海默氏病和其他形式的痴呆症没有直接相关,但记忆力下降对这些病的诊断至关重要,领导这项研究的Singh-Manoux博士对WebMD表示。

“我们研究并没有表明高密度脂蛋白和老年痴呆有关”,她说:“我们观察到中年时有认知能力下降,但是可以证明记忆力下降是痴呆症的一个风险因素。”

高密度脂蛋白低密度脂蛋白和记忆
研究人员试图对患阿茨海默氏病和与年龄相关痴呆症病人中的高密度脂蛋白及其它脂类如低密度脂蛋白、总胆固醇和肝油三脂等进行研究。但这些研究由于问题诸多而很难开展,Singh-Manoux说。

“在确诊之前,病人通常已患痴呆病多年,并且这种疾病本身可以改变脂蛋白特性,”她说。

最终,越来越多的研究人员开始关注痴呆症潜在的风险因素,因为在疾病确诊之前,这些风险因素就有表现。

伦刻大学Singh-Manoux和她的同事就采用了这种方法,

他们的这项研究有3673例公务员,为一项英国健康试验的受试者。受试者需定期进行血脂检验和记忆力下降的测试。

研究人员分析的数据主要来自两个时间段,受试者平均年龄在55岁时,以及之后在他们到61岁时。

高密度脂蛋白胆固醇低浓度定义为浓度低于40 mg/dL,而高浓度则为60 mg/dL以上。

研究人员观察期间发现高密度脂蛋白下降与相应记忆力的下降有关。

在平均年龄在61岁时,与体内高浓度的高密度脂蛋白的受试者相比,体内低浓度“好”胆固醇的受试者记忆力丧失的风险增加53%。

他汀类药物无助于记忆。

总胆固醉和肝油三脂的浓度与记忆力减退无关,应用他汀类药物似乎不影响记忆丧失。

他汀类药物降低低密度脂蛋白但对升高高密度脂蛋白没有明显效果,迄今为止,其他针对高密度脂蛋白的临床试验令人失望。

培养健康的生活方式-包括定期锻炼,保持体重,戒烟,这是升高高密度脂蛋白最好方法,美国心脏病协会发言人医学博士Martha Daviglus对WebMD表示。

“健康的生活方式能使每个人发生巨大变化”,她说,“众说周知,生活方式对降低各种疾病和不良状态的风险至关重要。

这项新的研究表明,早期养成健康的生活方式能改善中年时记忆力和认知功能,并可能预防后半生患痴呆症。

这项研究发表在美国心脏病协会《动脉硬化血栓血管生物学形成》8月期刊上。

“总胆固醇和低密度脂蛋白已确认为心脏病的风险因子,”Singh-Manoux说。“医生定期对这两项指标进行检测,但是我认为我们并没有对高密度脂蛋白给予足够的重视,我们研究结果表明高密度脂蛋白对记忆非常重要,因此医生和病人应当进行高密度脂蛋白的监测。”