Exercise may hold the key to youth, according to a study published on Monday which showed people who keep fit are up to nine years biologically younger than those who do not.

    The findings are the first to show in humans how keeping fit affects the ageing process.

    The study of 2,401 twins found that a sedentary lifestyle raises the risk of a range of problems from heart disease to cancer and appears to play a key role in the ageing process.

    It all appears to boil down to the length of structures called telomeres -- which protect the DNA on the chromosomes, the researchers from King's College London wrote in the Archives of Internal Medicine.

    Many studies have shown telomeres get shorter over time, suggesting the cells are ageing or dying. The study, which extracted a DNA sample from their volunteers, found people who exercised more each week had longer telomeres.

    Exercise lowers the risk of a range of problems such as heart disease, diabetes and cancer, the researchers said.

    "It is not just walking around the block. It is really working up a sweat," said Tim Spector, a genetic epidemiologist who led the study, in a telephone interview.

    The study found people who exercised vigorously 3 hours each week had longer telomeres and they were 9 years biologically younger than people who did under 15 minutes.

    Spector's team, who also adjusted for body weight, smoking, economic status and physical activity at work, also said moderate exercise for 1-1/2 hours each week provided a four-year advantage.

    Studying twins also provided a unique opportunity to gauge the effects of exercise on people with the same or similar genetic make-up, the researchers said.

    The reason why exercise has this effect is not clear but the researchers said they believe physical activity somehow defends against the natural process called oxidative stress, which damages and kills cells.

    本周一公布的一項研究表明，鍛煉身體是永葆青春的秘訣。研究發現，健身的人比不怎么鍛煉的人在生理上要年輕九歲。

    這個研究結果首次表明健身對于人衰老進程的影響。

    這項對2401對雙胞胎開展的研究發現，久坐的生活習慣會增大患心臟病和癌癥等一系列疾病的風險，而且是影響衰老進程的關鍵因素。

    倫敦國王學院的研究人員在《內科醫學檔案》中寫道，所有這些問題似乎都歸結于一種叫做“端粒”的特殊結構的長度，端粒能夠保護染色體上的DNA。

    很多研究已表明，隨著年齡的增長，端粒會變短，這意味著人體的細胞正在老化或死亡。研究人員從志愿者體內提取的DNA樣本中發現，每周鍛煉較多的人端粒較長。

    研究人員稱，鍛煉身體能夠降低患心臟病、糖尿病和癌癥等一系列疾病的風險。

    該研究負責人、遺傳流行病學家蒂姆•斯派科特在接受電話采訪時說：“這里所說的鍛煉并不只是簡單的散散步，而是要運動到出汗。”

    研究發現，每周進行3小時高強度鍛煉的人端粒較長，而且比每周鍛煉不到15分鐘的人在生理上年輕九歲。

    在排除體重、吸煙、經濟狀況和工作中的身體活動量等因素的影響后，斯派科特領導的研究小組發現，每周進行一至一個半小時的適度鍛煉仍可以讓你年輕四歲。

    此外，研究人員稱，對于雙胞胎的研究為衡量運動對于基因組成相同或相似的人所產生的影響提供了獨特的機會。

    雖然鍛煉能延緩衰老的原因目前還不清楚，但研究人員認為，運動在某種程度上抵抗了氧化應激的自然過程，這一過程會損壞或殺死細胞。