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.

周一公布的一項研究表明，體內若維生素B12含量較高，可能防止老年人腦萎縮。

研究人員稱這是個驚人的發現，但稱仍需更多資料，才會建議人們服用維生素B12補劑，以防止腦容量萎縮，甚至可能有助防止思維和記憶功能衰退。

牛津大學的David Smith和Anna Vogiatzoglou領導了此項研究。研究發現，體內B12水平最高的三組人群，出現腦萎縮的幾率是B12水平最低三組人群的六分之一左右。

研究對象為107名介于61-87歲的健康人，每年一次通過掃描記錄了各人的腦容量，并抽取血樣檢驗體內B12水平，此項工作持續五年。

研究人員表示，所有這些研究對象體內的B12水平均屬正常范圍。

負責牛津大學記憶力和老齡化調查項目的Smith表示：“研究雖然沒有切實證明，但還是暗示，我們也許可以通過調節體內B12水平來保護大腦，并可能避免認知能力減退。”

此項研究結果刊登在《神經病學雜志》上，Smith稱此次他們沒有研究服用B12補劑能否延緩腦萎縮的速度，但他參與的另一項研究正是著重于這個問題，預計研究結果將于明年見分曉。

他說道：“所以我們認為，現在就建議人們服用B12補劑來防止腦萎縮，還為時太早。”

Smith在電郵中寫道：“現在我們可以肯定的就是，人們可能最好令體內B12水平保持在正常范圍內的較高水準，而不是僅略高于正常與缺乏的分界線。”

他指出，要實現這點，可以食用大量富含B12的食物，譬如牛奶等奶制品、魚、肉和加強型的早餐谷物。

維生素B12可以促進紅細胞生成，同時對于中樞神經系統的保護也非常重要。缺少維生素B12會導致貧血和神經損傷。

Smith表示牛津大學去年的另一項研究顯示體內B12水平較低者（但仍在正在范圍之內）更容易發生認知能力損傷或者在以后有認知能力下降的高風險。

他說，“營養與大腦，尤其是癡呆之間的關系需要進行更多的研究。”

研究人員表示，在發達國家，維生素B12缺乏現象并不普遍，但是確實是存在于老年人中的一個問題。因為他們對于維生素的吸收存在問題。那些素食主義者體內的B12水平可能也會較低。但是在一些不發達國家，這就是一個嚴重的問題。比如，在印度70%的人群都存在B12缺乏現象。

哈佛大學的科學家進行的一項單獨研究（研究結果刊登在《自然-遺傳學》雜志上）顯示FUT2基因變異會影響到維生素B12在血液中的水平