If you are wondering how your brain is aging, just look in the mirror. New research has drawn a link between aging of skin and aging of the brain.
As we age, the brain loses neurons and glia, and the number of connections between neurons decreases. Protein clutter begins to accumulate inside brain cells and gather around them. Mental processing slows down. It becomes harder to remember and learn. All of this is normal aging, but not everyone's brain ages at the same rate.
There are some things you can do to keep your brain as young as possible, including physical exercise and keeping mentally active, and there are many abuses that will cause premature brain aging, including alcoholism, poor cardiovascular health and exposure to toxins, stress, infection and injury. Aging, like most things in biology, is a mixture of one's genes and one's environment.
Skin, just like the brain, changes dramatically as we age, but different individuals age at different rates, according to one's particular set of inherited genes. External factors, such as exposure to the sun, cause premature aging of skin. Scientists have compared the biochemical changes in skin on the buttocks (a region protected from the sun) with changes in skin on the forearms (a region exposed the sun), and this has given them insight into the genetic factors that cause skin aging, and the environmental factors that age skin prematurely. The findings point to many of the same processes at work in aging the brain.
Perhaps the biggest factor is hormones. Hormonal surges during puberty are clearly seen as skin problems in adolescence. Skin mirrors the first signs of aging, due to the hormonal decline in the body accompanying aging, and as hormone levels decline, the effects on the skin are plain to see. Skin becomes thin, dry and pale in color, and it begins to form multiple fine wrinkles. But the brain is also affected by the decline in hormones. Dementia can, in some cases, be attributed clearly to hormonal deficiencies. Estrogen therapy alone or in combination with progestin treatment increases the risk of mild dementia and cognitive impairment. Interestingly, sweat glands and sebaceous glands contribute to the production of sex hormones, and they also contain the enzymes that convert testosterone to estrogen. As the levels of hormones circulating in the blood decline with age, the skin partly overtakes the function of the gonads in synthesis of sex hormones.
In many cases, environmental factors that cause aging of skin and brain cells act on the same biochemical processes that age tissue naturally. Skin aged prematurely by the sun shows deep wrinkling and develops many kinds of pigment changes. This is caused by photo damage that stimulates the body's immune response to damaged cells, which triggers inflammation. Chronic inflammation is also seen in premature brain aging, such as in Alzheimer's disease. Researchers Evgenia Makrantonaki and colleagues in Germany find that both chronological skin aging and aging of skin caused by photo damage are associated with a decline in the biological processes of lipid synthesis, cholesterol synthesis and fatty acid synthesis. Brain aging is also associated with such changes, as well as with increased chronic inflammation caused by some of the same immune system chemicals.
The biological reason that skin and brain age in similar ways is that in the early embryo, both skin cells and brain cells develop from the same kind of embryonic tissue (ectoderm). It is not feasible to do a brain biopsy to assess aging of cerebral tissue, but a skin biopsy is simple. Skin cells can also provide an experimental model for aging research on the brain, for studies of the effects of hormones, pathogens and genetic factors on aging.
Preventing premature aging of the brain may not be as easy as preventing premature aging of skin with sun screen, but a careful look at your skin could tell you how well you are doing below the surface.