試想一下，當你參加大學畢業20周年同學會的時候，也許你會對同學們的變化產生疑問。盡管大家年齡相差不大，但彼此衰老的程度卻不相同。

　　大多數關於衰老的研究，都聚焦於老年人。但是，來自美國、英國、以色列和新西蘭的一個研究團隊認為，要想預防衰老相關的疾病，應該對年輕人的衰老過程進行研究。他們利用了18項研究指標，聯合測試出一個人是比同齡人老化得快還是慢。相關研究結果於近日發表在PNAS雜誌上。

　　在這項研究中，954名實際參與者在他們26、32及38歲時，分別接受了18項分子標記物的測試。這些測試包括腎髒，肝髒，肺髒及代謝和免疫係統的功能。研究人員還檢測了高密度脂蛋白、心肺功能和端粒的長度（端粒長度會隨著年齡增加而縮短），以及牙齒的健康程度和眼底微小血管的情況（這項可代表大腦的血管情況）。根據這些測試結果，研究人員們可以繪出每一個變量的曲線圖，這18項曲線圖可以推斷出每一個個體的衰老速度。大多數參與者與他們的實際年齡相當，然而，有些人每年實際衰老了3歲，有些人卻並無衰老，後者這些"凍齡人"比他們的實際年齡要年輕。

　　此外，研究人員將這些參與者在38歲時的臉部照片，給Duke大學的本科生們看，並要求學生們根據這些參與者們看上去的年輕程度，排出順序。調查結果顯示，那些生物學上，內髒器官功能比較老的參與者，他們看上去也比較老。

　　衰老的過程並不全都是基因遺傳決定，因為在對雙胞胎衰老的研究中發現，隻有20%的衰老歸結於基因因素，外部環境影響也是巨大的。此項研究提供了一些方法，提示我們可以聯合多項檢查，推測衰老進程或者評估一些治療衰老的效果。

　　doi: 10.1073/pnas.1506264112

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　　Quantification of biological aging in young adults

　　Daniel W. Belsky, et al.

　　Antiaging therapies show promise in model organism research. Translation to humans is needed to address the challenges of an aging global population. Interventions to slow human aging will need to be applied to still-young individuals. However, most human aging research examines older adults, many with chronic disease. As a result, little is known about aging in young humans. We studied aging in 954 young humans, the Dunedin Study birth cohort, tracking multiple biomarkers across three time points spanning their third and fourth decades of life. We developed and validated two methods by which aging can be measured in young adults, one cross-sectional and one longitudinal. Our longitudinal measure allows quantification of the pace of coordinated physiological deterioration across multiple organ systems (e.g., pulmonary, periodontal, cardiovascular, renal, hepatic, and immune function). We applied these methods to assess biological aging in young humans who had not yet developed age-related diseases. Young individuals of the same chronological age varied in their "biological aging" (declining integrity of multiple organ systems). Already, before midlife, individuals who were aging more rapidly were less physically able, showed cognitive decline and brain aging, self-reported worse health, and looked older. Measured biological aging in young adults can be used to identify causes of aging and evaluate rejuvenation therapies.