Bad news for those with bulging bellies: fat that builds up around the waist during middle age may cause dementia decades later, say researchers who examined the health records of thousands of senior citizens.

Scientists already know that overweight adults risk developing diabetes, heart problems and other medical conditions. But over the last few years researchers have noticed that obesity in middle age is linked with cognitive problems in the aged.

Now it seems that overall body mass is not so important – it's the fat around the belly that appears to cause the problems.

Epidemiologist Rachel Whitmer and colleagues looked at the medical records of 6583 adults registered with the healthcare firm she works for – Kaiser Permanente of Oakland, California.

During the 1960s and 1970s, records were taken of the diameters of the adults' bellies, which gave Whitmer a rough idea of how much fat they were carrying around the waist.
Metabolically active

When she compared the measurements with the subjects' current medical records, the results were startling. Incidence of dementia increased steadily with the amount of belly fat, such that the 20% with the most belly fat were over two and half times more likely to develop dementia that those carrying the least.

Levels of total fat also seemed to increase dementia risk, but not by the same magnitude.

"This is an important paper," says Sudha Seshadri, a neurologist at Boston University who has also found evidence linking belly fat to cognitive problems. "I believe the effect is real."

The link may seem odd, but Whitmer notes that the fat around the belly is the most metabolically active of all fat types.

For example, it secretes larger amounts of cytokines, molecules that carry chemical signals between cells. Some of these molecules, such as leptin, have been shown in animal studies to cross the blood-brain barrier, suggesting a mechanism by which extra weight around the belly could be affecting the brain.
Slimming exercise

Yet Seshadri also notes that factors other than fat could be responsible for the results. Whitmer's team controlled for some of these, such as education and rates of other illnesses. But other issues were not taken into account. Overweight people are less likely to exercise, for instance. Physical activity is known to decrease obesity risk, as well as being psychologically beneficial.

Whitmer acknowledges this short-coming, but points out that the dementia rates were greater among those who were not overweight during middle-age, but did have high levels of belly fat. These people are likely to have exercised since their weight was normal, she says, but they still went on to develop cognitive problems.

Researchers next need to study the impact that the molecules released by body fat have on the brain. If Whitmer's hypothesis proves right, the conclusions could be disturbing – those beer bellies may be silently damaging the brain, long before old age sets in.

But she notes that there are also grounds for optimism, since moderate exercise and diet can reduce weight around the belly more easily that it can in other parts of the body.

"It's the least stubborn fat," Whitmer says.
   對于大腹便便者來說這是個不幸的消息: 研究者在仔細查閱了成千上萬的老年人健康記錄后作出結論，中年人腰部的贅肉可能會成為幾十年后患老年癡呆癥的誘因.

科學家已經查明超重的成年人更容易患糖尿病, 心臟疾病和其他病癥. 然而在過去幾年里研究人員發現中年肥胖與老年時發生認知障礙有關聯.

如今看來似乎身體肥胖并非如此緊要 – 而是啤酒肚上的脂肪造成了這種疾患。

流行病學家Rachel Whitmer和他的同事查看了6583名成年人的醫療記錄，這些患者都在她工作的保健公司——加利福尼亞奧克蘭的Kaiser Permanente 公司做過登記。

20世紀60年代到70 年代，該公司測量了這些成年患者的腹部直徑，Whitmer 據此大致了解了他們在這個部位上含有多少脂肪。

新陳代謝旺盛

當她把測量結果與患者現在的醫療報告進行比較后 ，發現了一個驚人的事實. 老年癡呆癥的發生隨著腹部脂肪的含量成正比例增長, 例如與肚子較小的人相比，20% 啤酒肚最大的病人患老年癡呆癥的幾率是前者的兩倍半.

全身肥胖似乎也會增加患癡呆癥的幾率，但是遠比不上腹部發胖造成的影響。

"這是一個重要的報告,"波斯頓大學的神經學家Sudha Seshadri說, 他也發現啤酒肚與認知障礙有顯著的關聯性. "我認為這種影響是真實的."

這種關聯看起來似乎稀奇古怪, 但是Whitmer注意到在所有的脂肪類型中，肚子周圍的脂肪新陳代謝是最活躍的.

比方說, 它分泌大量能在細胞間傳遞化學信號的細胞因子,分子。 其中有些分子, 如瘦素, 在動物實驗中已經表明能夠穿越腦血管屏障, 促成這樣一個機制，即腹部過胖能影響到大腦.

瘦身運動

Seshadri 也注意到了脂肪以外造成癡呆的原因. Whitmer的團隊控制了其他一些因素, 例如教育和其他疾病. 但是還有一些原因沒有考慮進來. 比如說肥胖的人不太喜歡運動. 眾所周知運動可以降低患癡呆的危險, 而且有利于心理健康.

Whitmer 承認了這個缺陷, 但是指出那些中年時雖然沒有超重，但腹部脂肪含量確實過多的人到了老年癡呆癥發病率更高. 她說，這些人也許鍛煉過，因為他們的體重正常 ,但還是發生了認知障礙.

研究者接下來需要研究身體脂肪釋放出來的分子對大腦造成的影響. 如果 Whitmer的假說成立，這個結論會讓人困擾– 雖然還遠未到老年，那些啤酒肚卻已經悄聲無息地在損傷著大腦了.

但她說仍然有值得樂觀的地方, 因為適量的運動和節食可以更加容易地減消腹部脂肪，而其他的部位就沒有這么容易達到減肥效果.

"這是最不頑固的脂肪," Whitmer 說.