Aging is a process that happens to all of us, but it happens faster to some than to others. Did you know that different internal organs age differently, or that aging doesn't happen continuously, but in phases?

Here are 9 studies that have recently shed new light on the process of aging, potentially leading to new ways of tackling age-related diseases worldwide.

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1. Childhood trauma can have a great impact on DNA

Our early formative years greatly shape who we are in our later lives. There is even physical evidence of this in our DNA.

One study recently found that people who suffer major depression are biologically older than healthy people by an average of 8 months. This effect is strongest in people who have suffered some kind of childhood trauma, including violence, sexual abuse, or neglect.

The study was carried out with the help of 811 depressed patients and 319 control subjects from the Netherlands Study of Depression and Anxiety, that had blood samples drawn to allow researchers to test how their DNA had changed with age.

2. Your brain ages faster if you're depressed

The same aging is also present in a depressed person's brain. Recent research from Yale University showed that depression can physically change a person’s brain. In doing so it can speed up the brain's aging process, making depressed people more susceptible to illnesses associated with old age.

Irina Esterlis, a researcher at the Yale School of Medicine, presented her findings on February 14 at the American Association for the Advancement of Science conference in Washington DC.

3. The female brain stays metabolically younger than the male brain

Aging isn't the same for everyone, and it turns out that, generally speaking, women have an advantage when it comes to the brain's aging process. The human brain tends to shrink with age for men and women. However, a study published last year detailed how men's brains deteriorate faster than women's.

The study, from Washington University School of Medicine in St. Louis, found that women's brains appear, on average, to be three years younger, metabolically speaking, than men's of the same chronological age.

121 women and 84 men, of ages ranging from 20 to 82 years old, underwent PET scans to determine the flow of oxygen and glucose to their brains. For each person, the researchers measured the brain's metabolism by determining the amount of sugar committed to glycolysis in different regions of the brain. The findings might explain why women generally experience less cognitive decline than men in their later years.

4. Scientists identified three important phases of aging

According to another set of findings derived from a large number of blood tests, there are three important ages when it comes to the aging process: 34 years, 60 years and 78 years.

A team analyzed data from the blood plasma of 4,263 people, aged 18 to 95. They looked at the levels of approximately 3,000 different proteins moving through the plasma. Of those 3,000 proteins, 1,379 were shown to vary with age.

"By deep mining the aging plasma proteome, we identified undulating changes during the human lifespan," the researchers, from the Stanford Alzheimer's Disease Research Center (ADRC), wrote in their published paper.

Though the protein levels the researchers found in the blood plasma typically stayed relatively constant, big shifts in the levels were found to occur at the ages of 34, 60 and 78.

Though the reason for this happening is not yet fully understood, it suggests that aging doesn't occur continuously as it typically believed; instead, it might happen to us in phases.

5. Serotonin levels could be a key factor in aging

Levels of the chemical Serotonin contribute to our happiness and wellbeing, so it's no wonder that it also plays a role in the aging process.

“Now that we have more evidence that serotonin is a chemical that appears affected early in cognitive decline, we suspect that increasing serotonin function in the brain could prevent memory loss from getting worse and slow disease progression,” Gwenn S. Smith, Ph.D., of Johns Hopkins University School of Medicine, said in a press release in 2017.

In order to analyze the role of serotonin in cognitive impairment, the researchers carried out MRI and high-resolution PET scans on 28 individuals with mild cognitive impairment as well as on 29 healthy individuals that acted as controls. The average mean age was approximately 66 years.

"The reduction in [serotonin transporters] is associated with greater impairment in auditory-verbal and visual-spatial memory in [mild cognitive impairments],” the researchers wrote.

“Studies are in progress to determine whether serotonin degeneration may be involved in the transition from [mild cognitive impairments] to dementia and to relate serotonin degeneration to other aspects of [Alzheimer’s disease] neuropathology (eg, beta-amyloid and tau).”

7. Researchers identify a key protective gene

Researchers may have found the key to aging — by that, we mean the key gene. Depending on the version of a particular gene that you have, you might start aging very rapidly at the age of 65, or you might not.

The study, published in the journal Cell Systems, identifies a gene called TMEM106B that kicks into action at about the age of 65. One version of this gene offers protection against a host of age-related neurological diseases, including dementia, while another faulty version leads to rapid decline.

The two researchers behind the study analyzed genetic data from more than 1,200 autopsied human brains of people who had not been diagnosed with a neurodegenerative disease while alive. In doing so, they were able to single out the role of TMEM106B in brain aging.

8. Scientists have reversed aging in mice brain stem cell

Research published last year in Nature revealed how growing brain stiffness as we age causes brain stem cell dysfunction. Incredibly, it also showed how older stem cells can be reverted to a younger, healthier state.

A research team, made up of scientists at the Wellcome-MRC Cambridge Stem Cell Institute (University of Cambridge), studied young and old rat brains in order to understand the impact that age-related brain stiffness has on the function of oligodendrocyte progenitor cells (OPCs) — a type of brain stem cell that's important for maintaining normal brain function.

In order to discover whether the loss of function in older OPCs was reversible, the scientists transplanted aged OPCs from older rats into the brains of younger animals. The older brain cells were, impressively, rejuvenated. The findings could have great implications for the treatment of degenerative neurological diseases.

9. Outlining the future of brain research

Of course, there is still a lot we do not know about how the brain ages and how it functions. With that in mind, a group of scientists recently outlined, in a paper published in Nature, what they believe to be key areas of future research that will help to guide the brain science of the future.

1. Characterize the spectrum of brain aging.

2. Continue to open up more, expertly curated, datasets.

3. Externally validate brain-aging models.

4. Identify individual spatial patterns of brain aging.

5. Recognize the continuum of aging and disease.

6. Integrate more closely with biogerontology.

7. Aim for greater clinical applicability.

As the authors of the study from King's College London explain, "the aging process does not affect people uniformly; nor, in fact, does the aging process appear to be uniform even within an individual."

There is a lot that we do not yet understand about the process of getting older but, year by year, researchers are piecing the dots together.