Lord Kelvin, one of the greatest physicists in history, said that only when you can measure what you are talking about, and express it in numbers, do you know anything about it. If not, he claimed, your knowledge is poor and unsatisfactory. Precise and ubiquitous measurement is behind the immense technological progress of the last century and a half, and also behind personalized medicine. This precision medicine aims to cure each individual’s particular disease with personalized treatments, and although it is not a disease, aging is behind all diseases. Kelvin, who lived in the 19th century and predicted the death of the universe with his second law of thermodynamics, knew as well as we do that we all age, but he would not have been able to express it in numbers, beyond calendar years, or explain why each person ages at a different rate.
Recently, a team of scientists led by Christos Davatzikos, from the University of Pennsylvania (USA), has published in Nature Medicine A study that has identified different ways in which our brains break down as we age and that promises a more individualized measure of aging. They analyzed 50,000 brain scans that revealed five distinct forms of brain atrophy associated with aging and the onset of neurodegenerative diseases. Although the human eye cannot detect the subtle changes that exist between these five patterns, they were able to identify them using machine learning technology. The authors trained an algorithm by showing it scans of 1,150 healthy people between the ages of 20 and 50 and almost 9,000 people aged 20 and older, both healthy and cognitively impaired.
The particular patterns of ageing are related to individual biological traits, such as those that make some people more prone to diabetes and others to cardiovascular disease, but patterns were also seen that were more related to habits such as alcohol or tobacco consumption. And there is also a combination of patterns. People with mild cognitive impairment, which precedes dementia, accumulate traits from each of the patterns, although the presence of one of them was the one that most helped to predict the risk of dementia years later. In general, as was to be expected, the state of other organs was reflected in brain ageing.
Davatzikos warns that this type of knowledge would not allow us to “talk about treatments in the near future.” “This work helps us understand the heterogeneity of brain aging in general, which is caused by several possible underlying pathologies, including Alzheimer’s and Parkinson’s, and also factors related to cardiovascular and metabolic health.” “For now, the most immediate benefit could be seen in clinical trials, which benefit from recruiting individuals with more homogeneous profiles, which allows for detecting more subtle treatment effects with smaller samples,” explains the researcher.
Other recent work has looked for signals that might help predict the risk of accelerated cognitive decline starting in your 40s or 50s. The hippocampus, a key region in creating new memories, has been shown to shrink with age, but may do so more rapidly in middle age. Because brain scans are not a cheap and easy way to measure these changes, scientists have looked for alternative ways to see if brain aging may be speeding up. A team at Johns Hopkins University (USA) assessed cognitive decline in more than 12,000 people over 20 years and compared it to an estimate of their inflammation levels, which could be measured in blood tests. Those in the top 25% had nearly 8% greater cognitive decline than those in the bottom 25%. This effect of aging on the brain, which has a greater impact after age 40, could be measured with a blood test and combated with exercise, which has anti-inflammatory effects, or other neuroprotective treatments tailored to a particular pattern of brain aging.
In a job led by Richard Bethlehemfrom the University of Cambridge, an international collaboration of scientists sought to identify the main changes that occur in the brain throughout life. Among other things, Bethlehem said in The Conversationthey found that the number of neurons increases from before birth to a maximum at age six, and declines from there. The number of brain connections continues to grow until age 29 and begins to decline gradually until age 50. From that age onwards, the loss of connections accelerates.
Studies like this one and the one just published by Nature Medicine aim to identify specific changes in the brain that will allow us to standardize the precise measurement of each person’s aging. This will help us overcome the poor and unsatisfactory knowledge that Kelvin talked about and improve our ability to do something about aging.
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