Bursts of Human Aging: The Skin Chapter 爆发式衰老漫谈 — 皮肤篇
衰老双峰 — 44和60
过去我们以为人类衰老是像曲线一样逐渐下滑的，而今《自然-衰老》期刊发现我们是在44岁和60岁左右雪崩一样“爆发衰老”的 [1,2]。40多岁中期的变化，之前没有预料到，影响了男女的皮肤、肌肉和心血管健康相关的分子。在60岁初期，观察到与免疫力、肾功能和碳水化合物代谢相关的分子发生变化。这些发现挑战了衰老是一个稳定的、按时间顺序线性进程的观念，表明生物衰老遵循更复杂的模式，伴随着加速的阶段。
在40多岁时，与酒精、咖啡因和脂质代谢、心血管疾病以及皮肤和肌肉相关的分子数量发生了显著变化。而到60多岁时，分子数量变化与碳水化合物和咖啡因代谢、免疫调节、肾功能、心血管疾病以及皮肤和肌肉相关。这些发现解释了为什么某些与年龄相关的疾病，在美国，心血管疾病（包括动脉粥样硬化、中风和心肌梗死）的患病率在40至59岁之间约为40%，在60至79岁之间增加到约75%，在80岁以上的人群中达到约86%。神经退行性疾病（如帕金森病和阿尔茨海默病）的患病率随着人类老龄化的进展也呈上升趋势，并分别在40岁和65岁左右出现明显的转折点。酒精代谢功能的障碍可能与40多岁时酒精消费的增加有关，这通常是一个充满压力的生活阶段。
“We’re not just changing gradually over time; there are some really dramatic changes,” said Michael Snyder, PhD, professor of genetics and the study’s senior author. “It turns out the mid-40s is a time of dramatic change, as is the early 60s. And that’s true no matter what class of molecules you look at.”
人们需要关注自己的健康，尤其是在40多岁和60多岁时。这可能包括增加锻炼以保护心脏和维持肌肉质量，或在40多岁时减少酒精消费，因为这时酒精代谢能力减慢。
漫谈皮肤衰老
假设达尔文是正确的，人类选择褪去一身浓郁的毛发、变薄皮肤，虽然便于原始时代奔跑散热，但是失去了天然保护屏障，姑且不谈没有衣服在冬天就没法生存，而且当今我们已经没有那么多奔跑排汗散热的需求，新陈代谢速度变慢，皮下脂肪储备减少，皮肤缺水导致加速老化，细胞间距增大活性降低，没有胶原蛋白和脂肪支撑的皮肤变得松弛下垂，没有弹性。人类的皮肤越来越薄越来越脆弱，如今厚不过一张信用卡，进入衰老后，角质层更加缺水变薄，泛红过敏。
人类在皮肤层面呈现出衰老特征，中年油腻，老年干燥，这比我们的祖先猩猩明显很多，同时紫外线辐射对真皮层的伤害也暴露出人类脱毛进化的短视。如果我们的确是演化而来的，那么我们的审美引导了皮肤毛发的演化，当年我们喜欢皮糙毛多的靓女，她们刚从树上下来，健康活泼，荷尔蒙四射，现在我们喜欢细皮鲜肉的， 那些长毛糙皮的基因没有被选择，黯然离场渐渐的绝种了。
Two Crests — 44 and 60
Recent research published in Nature Aging challenges our previous understanding of human aging. Rather than a gradual decline, we experience “aging bursts” around ages 44 and 60 [1,2]. These findings reveal unexpected changes in skin, muscle, and cardiovascular health-related molecules in our mid-40s, while early 60s see shifts in molecules linked to immunity, kidney function, and carbohydrate metabolism. This new perspective suggests that biological aging follows a more complex pattern with accelerated phases, contradicting the notion of a steady, linear process.
The study observed significant changes in molecules associated with alcohol, caffeine, and lipid metabolism, cardiovascular disease, and skin and muscle health in the 40s. In the 60s, molecular changes related to carbohydrate and caffeine metabolism, immune regulation, kidney function, cardiovascular disease, and skin and muscle health were noted. These discoveries help explain the prevalence of age-related diseases. For instance, in the United States, cardiovascular disease rates increase from about 40% in the 40-59 age group to approximately 75% in the 60-79 age group, reaching about 86% in those over 80. Neurodegenerative diseases like Parkinson’s and Alzheimer’s also show marked increases around ages 40 and 65, respectively.
These findings emphasize the importance of prioritizing health, especially in our 40s and 60s. This may include increasing exercise to protect heart health and maintain muscle mass or reducing alcohol consumption in our 40s when metabolic capacity slows down.
A Causal Discussion on Skin Aging
Assuming Darwin’s theory of evolution is correct, humans have evolved to shed their thick body hair and develop thinner skin. While this adaptation was beneficial for running and heat dissipation in primitive times, it also resulted in the loss of our natural protective barrier. This change presented challenges, such as difficulty surviving in cold environments without clothing.
In modern society, our lifestyle has changed dramatically. We no longer need to run frequently to dissipate heat, and our metabolic rates have slowed accordingly. These changes have led to a series of physiological issues: reduced subcutaneous fat reserves, increased susceptibility to skin dehydration, and consequently, accelerated aging. Cell spacing has increased while cellular activity has decreased, and with the reduction of collagen and fat support, skin has become loose, sagging, and less elastic.
Human skin has become progressively thinner and more fragile, with an average thickness now not exceeding 4 millimeters. As we age, especially in later years, the stratum corneum becomes more dehydrated, thinner, and prone to redness and allergic reactions.
Compared to our primate ancestors, human skin exhibits more pronounced aging characteristics. Skin often becomes greasy middle-aged and dry old-aged. Moreover, due to the reduction in body hair, our skin is more susceptible to UV radiation damage, exposing the limitations of human hairless evolution in certain aspects.
From an evolutionary perspective, our aesthetic preferences may have guided the evolution of skin and hair to some extent. Early humans likely preferred individuals with rough skin and abundant hair, characteristics consistent with ancestors transitioning from arboreal to terrestrial life, symbolizing health and vitality. However, over time, our aesthetic standards shifted towards preferring individuals with smooth, delicate skin. This shift in preference may have led to individuals with genes for dense body hair and rough skin being at a reproductive disadvantage, ultimately resulting in the gradual reduction of these genes in the human population.
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Reference
- Shen, X., Wang, C., Zhou, X. et al. Nonlinear dynamics of multi-omics profiles during human aging. Nat Aging (2024)
- Stanford Medicine. Massive biomolecular shifts occur in our 40s and 60s, Stanford Medicine New Centre, Time marches on predictably, but biological aging is anything but constant, according to a new Stanford Medicine study.
