Having higher vitamin B12 levels may protect against brain shrinkage in elderly people, according to a study published on Monday.
The researchers called their findings striking, but said more information is needed before recommending that people take vitamin B12 supplements to guard against the loss of brain volume and possibly prevent declines in thinking and memory.

In the study led by David Smith and Anna Vogiatzoglou of the University of Oxford in Britain, people in the upper third of vitamin B12 levels were six times less likely to experience brain shrinkage than those in the lowest third.

The study involved 107 healthy people ages 61 to 87 who underwent scans to measure brain volume and gave blood samples to assess vitamin B12 levels once a year for up to five years.

All of those in the study had vitamin B12 levels classified in what is considered the normal range, the researchers said.

"Our study suggests, but does not prove, that by modifying our vitamin B12 status we might be able to protect our brain and so possibly prevent cognitive decline," said Smith, who heads the Oxford Project to Investigate Memory and Ageing.

The study, published in the journal Neurology, did not look at whether taking vitamin B12 supplements would slow the rate of brain shrinkage, Smith said. Another study in which he is involved focuses on that question, with the results expected in 2009, Smith added.

"So, we think it is too early to advise people to take B12 supplements to prevent their brains from shrinking," he said.

"What we can say is that our results suggest that rather than maintaining one's B12 at a level that is just above the cut-off for deficiency, it might be prudent to aim to keep it higher up the normal range," Smith said by e-mail.

Smith said that could be achieved by eating plenty of foods that are a good source of vitamin B12 such as milk and other dairy products, fish, meat and fortified breakfast cereals.

Vitamin B12 helps in the formation of red blood cells and is important for the maintenance of the central nervous system. Deficiency can lead to anemia and neurological damage.

Smith said another study from Oxford that came out last year showed that lower vitamin B12 levels -- but still within the normal range -- were linked to cognitive impairment and a higher risk of later cognitive decline.

"More research is needed into the relationship between nutrition and the brain, in particular dementia," Smith said.

Vitamin B12 deficiency is uncommon in developed countries but is an issue among the elderly due to problems in vitamin absorption and among vegetarians whose dietary intake may be low, the researchers said. But it is a serious problem in less developed parts of the world, Smith said, noting that in India around 70 percent of the people are vitamin B12 deficient.

A separate study led by Harvard University scientists in the journal Nature Genetics showed that common variations of a gene called FUT2 influence B12 vitamin levels in the blood.

周一公布的一项研究表明，体内若维生素B12含量较高，可能防止老年人脑萎缩。

研究人员称这是个惊人的发现，但称仍需更多资料，才会建议人们服用维生素B12补剂，以防止脑容量萎缩，甚至可能有助防止思维和记忆功能衰退。

牛津大学的David Smith和Anna Vogiatzoglou领导了此项研究。研究发现，体内B12水平最高的三组人群，出现脑萎缩的几率是B12水平最低三组人群的六分之一左右。

研究对象为107名介于61-87岁的健康人，每年一次通过扫描记录了各人的脑容量，并抽取血样检验体内B12水平，此项工作持续五年。

研究人员表示，所有这些研究对象体内的B12水平均属正常范围。

负责牛津大学记忆力和老龄化调查项目的Smith表示：“研究虽然没有切实证明，但还是暗示，我们也许可以通过调节体内B12水平来保护大脑，并可能避免认知能力减退。”

此项研究结果刊登在《神经病学杂志》上，Smith称此次他们没有研究服用B12补剂能否延缓脑萎缩的速度，但他参与的另一项研究正是着重于这个问题，预计研究结果将于明年见分晓。

他说道：“所以我们认为，现在就建议人们服用B12补剂来防止脑萎缩，还为时太早。”

Smith在电邮中写道：“现在我们可以肯定的就是，人们可能最好令体内B12水平保持在正常范围内的较高水准，而不是仅略高于正常与缺乏的分界线。”

他指出，要实现这点，可以食用大量富含B12的食物，譬如牛奶等奶制品、鱼、肉和加强型的早餐谷物。

维生素B12可以促进红细胞生成，同时对于中枢神经系统的保护也非常重要。缺少维生素B12会导致贫血和神经损伤。

Smith表示牛津大学去年的另一项研究显示体内B12水平较低者（但仍在正在范围之内）更容易发生认知能力损伤或者在以后有认知能力下降的高风险。

他说，“营养与大脑，尤其是痴呆之间的关系需要进行更多的研究。”

研究人员表示，在发达国家，维生素B12缺乏现象并不普遍，但是确实是存在于老年人中的一个问题。因为他们对于维生素的吸收存在问题。那些素食主义者体内的B12水平可能也会较低。但是在一些不发达国家，这就是一个严重的问题。比如，在印度70%的人群都存在B12缺乏现象。

哈佛大学的科学家进行的一项单独研究（研究结果刊登在《自然-遗传学》杂志上）显示FUT2基因变异会影响到维生素B12在血液中的水平